Crystals

12 pages, 3991 KiB

Open AccessEditor’s ChoiceArticle

Efficient Broadband Truncated-Pyramid-Based Metamaterial Absorber in the Visible and Near-Infrared Regions

by Phuc Toan Dang, Tuan V. Vu, Jongyoon Kim, Jimin Park, Van-Chuc Nguyen, Dat D. Vo, Truong Khang Nguyen, Khai Q. Le and Ji-Hoon Lee

Crystals 2020, 10(9), 784; https://doi.org/10.3390/cryst10090784 - 3 Sep 2020

Cited by 23 | Viewed by 3832

Abstract

We present a design of an ultra-broadband metamaterial absorber in the visible and near- infrared regions. The unit cell structure consists of a single layer of metallic truncated-pyramid resonator-dielectric-metal configuration, which results in a high absorption over a broad wavelength range. The absorber [...] Read more.

We present a design of an ultra-broadband metamaterial absorber in the visible and near- infrared regions. The unit cell structure consists of a single layer of metallic truncated-pyramid resonator-dielectric-metal configuration, which results in a high absorption over a broad wavelength range. The absorber exhibits 98% absorption at normal incidence spanning a wideband range of 417–1091 nm, with >99% absorption within 822–1054 nm. The broadband absorption stability maintains 95% at large incident angles up to 40° for the transverse electric (TE)-mode and 20° for the transverse magnetic (TM)-mode. Furthermore, the polarization-insensitive broadband absorption is presented in this paper by analyzing absorption performance with various polarization angles. The proposed absorber can be applied for applications such as solar cells, infrared detection, and communication systems thanks to the convenient and compatible bandwidth for electronic THz sources. Full article

(This article belongs to the Special Issue Plasmonic Nanostructures)

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21 pages, 10460 KiB

Open AccessEditor’s ChoiceArticle

Determination of Mechanical Characteristics for Fiber-Reinforced Concrete with Straight and Hooked Fibers

by Zuzana Marcalikova, Radim Cajka, Vlastimil Bilek, David Bujdos and Oldrich Sucharda

Crystals 2020, 10(6), 545; https://doi.org/10.3390/cryst10060545 - 25 Jun 2020

Cited by 43 | Viewed by 6960

Abstract

Fiber-reinforced concrete has a wide application in practice, and many fields of research are devoted to it. In most cases, this is a specific problem, i.e., the determination of the mechanical properties or the test method. However, wider knowledge of the effect of [...] Read more.

Fiber-reinforced concrete has a wide application in practice, and many fields of research are devoted to it. In most cases, this is a specific problem, i.e., the determination of the mechanical properties or the test method. However, wider knowledge of the effect of fiber in concrete is unavailable or insufficient for selected test series that cannot be compared. This article deals with the processing of a comprehensive test study and the impact of two types of fibers on the quantitative and qualitative parameters of concrete. Testing was performed for fiber dosages of 0, 40, 75, and 110 kg/m³. The fibers were hooked and straight. The influence of the fibers on the mechanical properties in fiber-reinforced concrete was analyzed by functional dependence. The selected mechanical properties were compressive strength, splitting tensile strength, bending tensile strength, and fracture energy. The results also include the resulting load–displacement diagrams and summary recommendations for the structural use and design of fiber-reinforced concrete structures. The shear resistance of reinforced concrete beams with hooked fibers was also verified by tests. Full article

(This article belongs to the Special Issue Cement-Based Composites: Advancements in Development and Characterization)

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56 pages, 65518 KiB

Open AccessEditor’s ChoiceReview

Microwave Liquid Crystal Enabling Technology for Electronically Steerable Antennas in SATCOM and 5G Millimeter-Wave Systems

by Rolf Jakoby, Alexander Gaebler and Christian Weickhmann

Crystals 2020, 10(6), 514; https://doi.org/10.3390/cryst10060514 - 16 Jun 2020

Cited by 82 | Viewed by 17206

Abstract

Future satellite platforms and 5G millimeter wave systems require Electronically Steerable Antennas (ESAs), which can be enabled by Microwave Liquid Crystal (MLC) technology. This paper reviews some fundamentals and the progress of microwave LCs concerning its performance metric, and it also reviews the [...] Read more.

Future satellite platforms and 5G millimeter wave systems require Electronically Steerable Antennas (ESAs), which can be enabled by Microwave Liquid Crystal (MLC) technology. This paper reviews some fundamentals and the progress of microwave LCs concerning its performance metric, and it also reviews the MLC technology to deploy phase shifters in different topologies, starting from well-known toward innovative concepts with the newest results. Two of these phase shifter topologies are dedicated for implementation in array antennas: (1) wideband, high-performance metallic waveguide phase shifters to plug into a waveguide horn array for a relay satellite in geostationary orbit to track low Earth orbit satellites with maximum phase change rates of 5.1°/s to 45.4°/s, depending on the applied voltages, and (2) low-profile planar delay-line phase shifter stacks with very thin integrated MLC varactors for fast tuning, which are assembled into a multi-stack, flat-panel, beam-steering phased array, being able to scan the beam from −60° to +60° in about 10 ms. The loaded-line phase shifters have an insertion loss of about 3 dB at 30 GHz for a 400° differential phase shift and a figure-of-merit (FoM) > 120°/dB over a bandwidth of about 2.5 GHz. The critical switch-off response time to change the orientation of the microwave LCs from parallel to perpendicular with respect to the RF field (worst case), which corresponds to the time for 90 to 10% decay in the differential phase shift, is in the range of 30 ms for a LC layer height of about 4 µm. These MLC phase shifter stacks are fabricated in a standard Liquid Crystal Display (LCD) process for manufacturing low-cost large-scale ESAs, featuring single- and multiple-beam steering with very low power consumption, high linearity, and high power-handling capability. With a modular concept and hybrid analog/digital architecture, these smart antennas are flexible in size to meet the specific requirements for operating in satellite ground and user terminals, but also in 5G mm-wave systems. Full article

(This article belongs to the Special Issue Microwave Liquid Crystal Technology)

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18 pages, 6431 KiB

Open AccessEditor’s ChoiceReview

A Survey of Supramolecular Aggregation Based on Main Group Element⋯Selenium Secondary Bonding Interactions—A Survey of the Crystallographic Literature

by Edward R. T. Tiekink

Crystals 2020, 10(6), 503; https://doi.org/10.3390/cryst10060503 - 12 Jun 2020

Cited by 12 | Viewed by 2540

Abstract

The results of a survey of the crystal structures of main group element compounds (M = tin, lead, arsenic, antimony, bismuth, and tellurium) for intermolecular M⋯Se secondary bonding interactions is presented. The identified M⋯Se interactions in 58 crystals can operate independent of conventional [...] Read more.

The results of a survey of the crystal structures of main group element compounds (M = tin, lead, arsenic, antimony, bismuth, and tellurium) for intermolecular M⋯Se secondary bonding interactions is presented. The identified M⋯Se interactions in 58 crystals can operate independent of conventional supramolecular synthons and can sustain zero-, one-, two, and, rarely, three-dimensional supramolecular architectures, which are shown to adopt a wide variety of topologies. The most popular architecture found in the crystals stabilized by M⋯Se interactions are one-dimensional chains, found in 50% of the structures, followed by zero-dimensional (38%). In the majority of structures, the metal center forms a single M⋯Se contact; however, examples having up to three M⋯Se contacts are evident. Up to about 25% of lead(II)-/selenium-containing crystals exhibit Pb⋯Se tetrel bonding, a percentage falling off to about 15% in bismuth analogs (that is, pnictogen bonding) and 10% or lower for the other cited elements. Full article

(This article belongs to the Special Issue σ- and π-Hole Interactions)

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28 pages, 6174 KiB

Open AccessFeature PaperEditor’s ChoiceReview

A Practical Review of the Laser-Heated Diamond Anvil Cell for University Laboratories and Synchrotron Applications

by Simone Anzellini and Silvia Boccato

Crystals 2020, 10(6), 459; https://doi.org/10.3390/cryst10060459 - 1 Jun 2020

Cited by 50 | Viewed by 9027

Abstract

In the past couple of decades, the laser-heated diamond anvil cell (combined with in situ techniques) has become an extensively used tool for studying pressure-temperature-induced evolution of various physical (and chemical) properties of materials. In this review, the general challenges associated with the [...] Read more.

In the past couple of decades, the laser-heated diamond anvil cell (combined with in situ techniques) has become an extensively used tool for studying pressure-temperature-induced evolution of various physical (and chemical) properties of materials. In this review, the general challenges associated with the use of the laser-heated diamond anvil cells are discussed together with the recent progress in the use of this tool combined with synchrotron X-ray diffraction and absorption spectroscopy. Full article

(This article belongs to the Special Issue Pressure-Induced Phase Transformations)

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16 pages, 5365 KiB

Open AccessEditor’s ChoiceArticle

Green Synthesis of ZnO Nanostructures Using Salvadora Persica Leaf Extract: Applications for Photocatalytic Degradation of Methylene Blue Dye

by Fahad A. Alharthi, Abdulaziz Ali Alghamdi, Asma A. Alothman, Zainab M. Almarhoon, Munairah F. Alsulaiman and Nabil Al-Zaqri

Crystals 2020, 10(6), 441; https://doi.org/10.3390/cryst10060441 - 30 May 2020

Cited by 38 | Viewed by 4667

Abstract

Various ZnO nanomaterials such as nanorods, nanoparticles, and nanosheets were synthesized using Salvadora persica leaf extract via the sol–gel method. The prepared nanomaterials possess a large number of nanocavities. The synthesized nanomaterials were characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), UV-visible [...] Read more.

Various ZnO nanomaterials such as nanorods, nanoparticles, and nanosheets were synthesized using Salvadora persica leaf extract via the sol–gel method. The prepared nanomaterials possess a large number of nanocavities. The synthesized nanomaterials were characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), UV-visible diffuse reflectance studies (UV-DRS), scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HT-TEM), and these nanomaterials were used to test photocatalytic applications for the degradation of highly hazardous methylene blue dye. The degradation efficiency was higher for materials with nanorods and nanosheets with nanocavities; this was due to the presence of the nanocavities, which made the catalyst more sensitive to light absorption. This method offers a green synthesis of different nanomaterials in bulk quantity at low cost. Full article

(This article belongs to the Special Issue Zinc Oxide Nanomaterials and Based Devices)

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8 pages, 3611 KiB

Open AccessEditor’s ChoiceArticle

Electromechanically Rotatable Cross-Shaped Mid-IR Metamaterial

by Jitong Zhong and Yu-Sheng Lin

Crystals 2020, 10(6), 431; https://doi.org/10.3390/cryst10060431 - 28 May 2020

Cited by 11 | Viewed by 2430

Abstract

We present an electromechanically rotatable infrared (IR) cross-shaped metamaterial (CSM) in the mid-IR wavelength range. The CSM configuration is composed of double gold layers with cross-shaped nanostructures. To investigate the fano-resonance within CSM nanostructures, the aspect ratios and length ratios of CSM are [...] Read more.

We present an electromechanically rotatable infrared (IR) cross-shaped metamaterial (CSM) in the mid-IR wavelength range. The CSM configuration is composed of double gold layers with cross-shaped nanostructures. To investigate the fano-resonance within CSM nanostructures, the aspect ratios and length ratios of CSM are compared and discussed. The electromagnetic responses exhibit the characteristics of large tuning range, tunable broad and narrow bandwidths. By properly tailoring the aspect ratio of CSM, the resonance can be tuned with bidirectional tuning in the range of 650 nm. CSM with different length ratios exhibit narrowband resonances around the wavelength of 4.6 μm and broadband resonances in the wavelength range of 5.0 μm to 6.5 μm. These characteristics of CSM with different aspect ratios and length ratios could be potentially used in IR narrowband and broadband filter. To further increase the flexibility of proposed electromechanically rotatable CSM, an actively tunable narrowband and broadband filter in the mid-IR wavelength range is performed. This study provides a unique approach to realizing an IR filter, with high flexibility. Full article

(This article belongs to the Special Issue Plasmonic Nanostructures)

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11 pages, 3531 KiB

Open AccessEditor’s ChoiceArticle

Reduced Sintering Temperatures of Li⁺ Conductive Li_1.3Al_0.3Ti_1.7(PO₄)₃ Ceramics

by Katja Waetzig, Christian Heubner and Mihails Kusnezoff

Crystals 2020, 10(5), 408; https://doi.org/10.3390/cryst10050408 - 20 May 2020

Cited by 36 | Viewed by 5204

Abstract

All-solid-state batteries (ASSB) are considered promising candidates for future energy storage and advanced electric mobility. When compared to conventional Li-ion batteries, the substitution of Li-ion conductive, flammable liquids by a solid electrolyte and the application of Li-metal anodes substantially increase safety and energy [...] Read more.

All-solid-state batteries (ASSB) are considered promising candidates for future energy storage and advanced electric mobility. When compared to conventional Li-ion batteries, the substitution of Li-ion conductive, flammable liquids by a solid electrolyte and the application of Li-metal anodes substantially increase safety and energy density. The solid electrolyte Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) provides high Li-ion conductivity of about 10⁻³ S/cm and is considered a highly promising candidate for both the solid electrolyte-separator and the ionically conductive part of the all-solid state composite cathode, consisting of the cathode material, the solid electrolyte, and an electron conductor. Co-sintering of the composite cathode is a sophisticated challenge, because temperatures above 1000 °C are typically required to achieve the maximum ionic conductivity of LATP but provoke reactions with the cathode material, inhibiting proper electrochemical functioning in the ASSB. In the present study, the application of sintering aids with different melting points and their impact on the sinterability and the conductivity of LATP were investigated by means of optical dilatometry and impedance spectroscopy. The microstructure of the samples was analyzed by SEM. The results indicate that the sintering temperature can be reduced below 800 °C while maintaining high ionic conductivity of up to 3.6 × 10⁻⁴ S/cm. These insights can be considered a crucial step forward towards enable LATP-based composite cathodes for future ASSB. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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14 pages, 5430 KiB

Open AccessEditor’s ChoiceArticle

Structural, Hirshfeld Surface Analysis, Morphological Approach, and Spectroscopic Study of New Hybrid Iodobismuthate Containing Tetranuclear 0D Cluster Bi₄I₁₆·4(C₆H₉N₂) 2(H₂O)

by Hela Ferjani

Crystals 2020, 10(5), 397; https://doi.org/10.3390/cryst10050397 - 15 May 2020

Cited by 21 | Viewed by 3484

Abstract

The Bi₄I₁₆·4(C₆H₉N₂) 2(H₂O) compound was synthesized by slow evaporation at room temperature. It exhibits a zero-dimensional (0D) tetrameric structure, comprising [Bi₄I₁₆]⁴⁻ distorted octahedra, with strong I⋯I [...] Read more.

The Bi₄I₁₆·4(C₆H₉N₂) 2(H₂O) compound was synthesized by slow evaporation at room temperature. It exhibits a zero-dimensional (0D) tetrameric structure, comprising [Bi₄I₁₆]⁴⁻ distorted octahedra, with strong I⋯I interactions among adjacent anionic clusters. We used Hirshfeld surface analysis to discuss the strength of hydrogen bonds and to quantify the inter-contacts (two-dimensional (2D) fingerprint plots). It revealed that the hydrogen bonding interactions H⋯I (56.3%), π–π stacking (11.7%), and I⋯I interactions (5.9%) play the major role in the stability of the crystal structure. The crystal morphology was simulated using Bravais–Friedel, Donnay–Harker (BFDH) and growth morphology (GM) methods. The experimental habit of the title compound was adequately reproduced by the two models. The calculated results show that the crystal morphology of the title compound in a vacuum is dominated by five facets: (020), (011), (110), (10−1), and (11−1). The (020) facet is the largest among all the facets calculated. Projection of the facet showed that there are a few polar groups on the (020) facet. In the 50–400 and 400–4000 cm⁻¹ frequency regions, we measured the Raman and infrared spectra, respectively, of the title compound, and we assigned the observed vibration modes. Full article

(This article belongs to the Special Issue Characterisation and Study of Compounds by Single Crystal X-Ray Diffraction)

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24 pages, 7637 KiB

Open AccessEditor’s ChoiceArticle

Enhancement of ZnO Nanorods Properties Using Modified Chemical Bath Deposition Method: Effect of Precursor Concentration

by Ahmed Fattah Abdulrahman, Sabah Mohammed Ahmed, Naser Mahmoud Ahmed and Munirah Abullah Almessiere

Crystals 2020, 10(5), 386; https://doi.org/10.3390/cryst10050386 - 9 May 2020

Cited by 39 | Viewed by 3954

Abstract

In this study, the effects of different precursor concentrations on the growth and characteristics properties of the zinc oxide (ZnO) nanorods (NRs) synthesized by using modified and conventional chemical bath deposition (CBD) methods were investigated. The morphologic, structural and optical properties of synthesized [...] Read more.

In this study, the effects of different precursor concentrations on the growth and characteristics properties of the zinc oxide (ZnO) nanorods (NRs) synthesized by using modified and conventional chemical bath deposition (CBD) methods were investigated. The morphologic, structural and optical properties of synthesized ZnO NRs with different precursor concentrations were studied using various characterization techniques. The experimental results show that the varying precursor concentration of the reactants has a remarkable and significant effect on the growth and characteristics properties of ZnO NRs. In addition, the characteristic properties of ZnO NRs grown using the modified method showed significantly improved and enhanced properties. The average length of grown ZnO NRs increased with increased precursor concentration; it can be seen that longer ZnO NRs have been investigated using the modified CBD methods. The ZnO NRs synthesized at 0.05 M using the modified method were grown with high aspect ratios than the ZnO NRs grown using conventional means which were 25 and 11, respectively. The growth rate increased with increased precursor concentration; it can be observed that a higher growth rate was seen using the modification CBD method. Furthermore, XRD results for the two cases reveal that the grown ZnO samples were a nanorod-like in shape and possessed a hexagonal wurtzite structure with high crystal quality. No other phases from the impurity were observed. The diffraction peaks along (002) plane became higher, sharper and narrower as precursor concentration increased, suggesting that the crystalline quality of ZnO NRs grown using the modified method was more enhanced and better than conventional methods. However, optical studies show that the transmittance at each concentration was more than two times higher than the transmittance using the modified CBD method. In addition, optical studies demonstrated that the ZnO NRs grown by using modified and conventional methods had a direct E_g in the range of (3.2–3.26) eV and (3.15–3.19) eV, respectively. It was demonstrated in two methods that ZnO NRs grown at a precursor concentration 0.05 M gave the most favorable result, since the NRs had best characteristic properties. Full article

(This article belongs to the Special Issue Zinc Oxide Nanomaterials and Based Devices)

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17 pages, 3634 KiB

Open AccessEditor’s ChoiceArticle

Parameter Estimation of the Stochastic Primary Nucleation Kinetics by Stochastic Integrals Using Focused-Beam Reflectance Measurements

by Joi Unno and Izumi Hirasawa

Crystals 2020, 10(5), 380; https://doi.org/10.3390/cryst10050380 - 7 May 2020

Cited by 9 | Viewed by 3615

Abstract

The kinetic parameters of stochastic primary nucleation were estimated for the batch-cooling crystallization of L-arginine. It is difficult for process analytical tools to detect the first nucleus. In this study, the latent period for the total number of crystals to be increased to [...] Read more.

The kinetic parameters of stochastic primary nucleation were estimated for the batch-cooling crystallization of L-arginine. It is difficult for process analytical tools to detect the first nucleus. In this study, the latent period for the total number of crystals to be increased to a predetermined threshold was repeatedly measured with focused-beam reflectance measurements. Consequently, the latent periods were different in each measurement due to the stochastic behavior of both primary and secondary nucleation. Therefore, at first, the distribution of the latent periods was estimated by a Monte Carlo simulation for some combinations of the kinetic parameters of primary nucleation. In the simulation, stochastic integrals of the population and mass balance equations were solved. Then, the parameters of the distribution of latent periods were estimated and correlated with the kinetic parameters of primary nucleation. The resulting correlation was represented by a map**. Finally, the parameters of the actual distribution were input into the inverse map**, and the kinetic parameters were estimated as the outputs. The estimated kinetic parameters were validated using statistical techniques, which implied that the observed distribution function of the latent periods for the thresholds used in the estimation coincided reasonably with the simulated one based on the estimated parameters. Full article

(This article belongs to the Special Issue Crystal Nucleation and Growth Kinetics)

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15 pages, 7684 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Photoaligning and Photopatterning: New LC Technology

by Vladimir Chigrinov, Jiatong Sun and **aoqian Wang

Crystals 2020, 10(4), 323; https://doi.org/10.3390/cryst10040323 - 20 Apr 2020

Cited by 39 | Viewed by 5484

Abstract

We demonstrate a physical model of photoalignment and photopatterning based on rotational diffusion in solid azo-dye nanolayers. We also highlight the new applications of photoalignment and photopatterning in display and photonics such as: (i) liquid crystal (LC) E-paper devices, including optically rewritable LC [...] Read more.

We demonstrate a physical model of photoalignment and photopatterning based on rotational diffusion in solid azo-dye nanolayers. We also highlight the new applications of photoalignment and photopatterning in display and photonics such as: (i) liquid crystal (LC) E-paper devices, including optically rewritable LC E-paper on flexible substrates as 3D E-paper, as well as optically rewritable technology for photonics devices; (ii) photonics LC devices, such as LC Switches, polarization controllers and polarization rotators, variable optical attenuators, LC filled photonic crystal fiber, switchable diffraction grating; (iii) patterned micro-polarizer array using photo-alignment technology for image sensor; (iv) electrically tunable liquid crystal q-plates; (v) electrically switchable liquid crystal Fresnel lens; (vi) liquid crystal optical elements with integrated Pancharatnam-Berry phases. We are sure, that in the field of (LC), the main point is no longer display research, but new photonic applications of LC are emerging in telecommunication, fiber optical communication systems, sensors, switchable lenses, LC light converters and other LC photonics devices. Full article

(This article belongs to the Special Issue Micro and Nano Patterned Substrates for Liquid Crystal Alignment (Volume II))

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26 pages, 12671 KiB

Open AccessEditor’s ChoiceReview

A Review of Acoustic Metamaterials and Phononic Crystals

by Junyi Liu, Hanbei Guo and Ting Wang

Crystals 2020, 10(4), 305; https://doi.org/10.3390/cryst10040305 - 15 Apr 2020

Cited by 167 | Viewed by 16273

Abstract

As a new kind of artificial material developed in recent decades, metamaterials exhibit novel performance and the promising application potentials in the field of practical engineering compared with the natural materials. Acoustic metamaterials and phononic crystals have some extraordinary physical properties, effective negative [...] Read more.

As a new kind of artificial material developed in recent decades, metamaterials exhibit novel performance and the promising application potentials in the field of practical engineering compared with the natural materials. Acoustic metamaterials and phononic crystals have some extraordinary physical properties, effective negative parameters, band gaps, negative refraction, etc., extending the acoustic properties of existing materials. The special physical properties have attracted the attention of researchers, and great progress has been made in engineering applications. This article summarizes the research on acoustic metamaterials and phononic crystals in recent decades, briefly introduces some representative studies, including equivalent acoustic parameters and extraordinary characteristics of metamaterials, explains acoustic metamaterial design methods, and summarizes the technical bottlenecks and application prospects. Full article

(This article belongs to the Special Issue Metamaterials)

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7 pages, 1285 KiB

Open AccessEditor’s ChoiceCommunication

Halogen Bonding in Isostructural Co(II) Complexes with 2-Halopyridines

by Sergey A. Adonin, Mikhail A. Bondarenko, Alexander S. Novikov and Maxim N. Sokolov

Crystals 2020, 10(4), 289; https://doi.org/10.3390/cryst10040289 - 10 Apr 2020

Cited by 26 | Viewed by 3285

Abstract

Three complexes [Co(2-XPy)₂Cl₂] (X = Cl, Br, and I) were prepared and characterized, representing a rare case of isostructurality within the Cl-Br-I row. The nature of halogen bonding (XB) in a solid state was studied by DFT calculations, revealing [...] Read more.

Three complexes [Co(2-XPy)₂Cl₂] (X = Cl, Br, and I) were prepared and characterized, representing a rare case of isostructurality within the Cl-Br-I row. The nature of halogen bonding (XB) in a solid state was studied by DFT calculations, revealing a tendency of XB energy growth for heavier halogens. Full article

(This article belongs to the Section Crystalline Materials)

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18 pages, 8446 KiB

Open AccessEditor’s ChoiceArticle

Zn Doped α-Fe₂O₃: An Efficient Material for UV Driven Photocatalysis and Electrical Conductivity

by Suman, Surjeet Chahal, Ashok Kumar and Parmod Kumar

Crystals 2020, 10(4), 273; https://doi.org/10.3390/cryst10040273 - 4 Apr 2020

Cited by 92 | Viewed by 6922

Abstract

Zinc (Zn) doped hematite (α-Fe₂O₃) nanoparticles with varying concentrations (pure, 2%, 4% and 6%) were synthesized via sol-gel method. The influence of divalent Zn ions on structural, optical and dielectric behavior of hematite were studied. X-ray diffraction (XRD) pattern [...] Read more.

Zinc (Zn) doped hematite (α-Fe₂O₃) nanoparticles with varying concentrations (pure, 2%, 4% and 6%) were synthesized via sol-gel method. The influence of divalent Zn ions on structural, optical and dielectric behavior of hematite were studied. X-ray diffraction (XRD) pattern of synthesized samples were indexed to rhombohedral R3c space group of hematite with 14–21 nm crystallite size. The lattice parameter (a and c) values increase upto Zn 4% and decrease afterwards. The surface morphology of prepared nanoparticles were explored using transmission electron microscopy (TEM). The band gap measured from Tauc’s plot, using UV-Vis spectroscopy, showed reduction in its values upto Zn 4% and the reverse trend was obtained in higher concentrations. The dielectric properties of pure and Zn doped hematite were investigated at room temperature and followed the same trends as that of XRD parameters and band gap. Photocatalytic properties of nanoparticles were performed for hazardous Rose bengal dye and showed effective degradation in the presence of UV light. Hence, Zn²⁺ doped hematite can be considered as an efficient material for the potential applications in the domain of photocatalysis and also higher value of dielectric constant at room temperature makes them applicable in high energy storage devices. Full article

(This article belongs to the Special Issue Structural, Magnetic, Dielectric, Electrical, Optical and Thermal Properties of Nanocrystalline Materials: Synthesis, Characterization and Application)

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27 pages, 1413 KiB

Open AccessEditor’s ChoiceReview

Towards an Optimal Sample Delivery Method for Serial Crystallography at XFEL

by Robert KY Cheng

Crystals 2020, 10(3), 215; https://doi.org/10.3390/cryst10030215 - 19 Mar 2020

Cited by 39 | Viewed by 6416

Abstract

The advent of the X-ray free electron laser (XFEL) in the last decade created the discipline of serial crystallography but also the challenge of how crystal samples are delivered to X-ray. Early sample delivery methods demonstrated the proof-of-concept for serial crystallography and XFEL [...] Read more.

The advent of the X-ray free electron laser (XFEL) in the last decade created the discipline of serial crystallography but also the challenge of how crystal samples are delivered to X-ray. Early sample delivery methods demonstrated the proof-of-concept for serial crystallography and XFEL but were beset with challenges of high sample consumption, jet clogging and low data collection efficiency. The potential of XFEL and serial crystallography as the next frontier of structural solution by X-ray for small and weakly diffracting crystals and provision of ultra-fast time-resolved structural data spawned a huge amount of scientific interest and innovation. To utilize the full potential of XFEL and broaden its applicability to a larger variety of biological samples, researchers are challenged to develop better sample delivery methods. Thus, sample delivery is one of the key areas of research and development in the serial crystallography scientific community. Sample delivery currently falls into three main systems: jet-based methods, fixed-target chips, and drop-on-demand. Huge strides have since been made in reducing sample consumption and improving data collection efficiency, thus enabling the use of XFEL for many biological systems to provide high-resolution, radiation damage-free structural data as well as time-resolved dynamics studies. This review summarizes the current main strategies in sample delivery and their respective pros and cons, as well as some future direction. Full article

(This article belongs to the Special Issue Macromolecular Serial Crystallography)

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35 pages, 12684 KiB

Open AccessEditor’s ChoiceReview

Applications of X-ray Powder Diffraction in Protein Crystallography and Drug Screening

by Maria Spiliopoulou, Alexandros Valmas, Dimitris-Panagiotis Triandafillidis, Christos Kosinas, Andrew Fitch, Fotini Karavassili and Irene Margiolaki

Crystals 2020, 10(2), 54; https://doi.org/10.3390/cryst10020054 - 21 Jan 2020

Cited by 16 | Viewed by 9055

Abstract

Providing fundamental information on intra/intermolecular interactions and physicochemical properties, the three-dimensional structural characterization of biological macromolecules is of extreme importance towards understanding their mechanism of action. Among other methods, X-ray powder diffraction (XRPD) has proved its applicability and efficiency in numerous studies of [...] Read more.

Providing fundamental information on intra/intermolecular interactions and physicochemical properties, the three-dimensional structural characterization of biological macromolecules is of extreme importance towards understanding their mechanism of action. Among other methods, X-ray powder diffraction (XRPD) has proved its applicability and efficiency in numerous studies of different materials. Owing to recent methodological advances, this method is now considered a respectable tool for identifying macromolecular phase transitions, quantitative analysis, and determining structural modifications of samples ranging from small organics to full-length proteins. An overview of the XRPD applications and recent improvements related to the study of challenging macromolecules and peptides toward structure-based drug design is discussed. This review congregates recent studies in the field of drug formulation and delivery processes, as well as in polymorph identification and the effect of ligands and environmental conditions upon crystal characteristics. These studies further manifest the efficiency of protein XRPD for quick and accurate preliminary structural characterization. Full article

(This article belongs to the Special Issue Advanced Methods to Monitor and Control the Crystallisation Environment)

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23 pages, 3258 KiB

Open AccessEditor’s ChoiceReview

Pressure-Tuned Interactions in Frustrated Magnets: Pathway to Quantum Spin Liquids?

by Tobias Biesner and Ece Uykur

Crystals 2020, 10(1), 4; https://doi.org/10.3390/cryst10010004 - 18 Dec 2019

Cited by 12 | Viewed by 5999

Abstract

Quantum spin liquids are prime examples of strongly entangled phases of matter with unconventional exotic excitations. Here, strong quantum fluctuations prohibit the freezing of the spin system. On the other hand, frustrated magnets, the proper platforms to search for the quantum spin liquid [...] Read more.

Quantum spin liquids are prime examples of strongly entangled phases of matter with unconventional exotic excitations. Here, strong quantum fluctuations prohibit the freezing of the spin system. On the other hand, frustrated magnets, the proper platforms to search for the quantum spin liquid candidates, still show a magnetic ground state in most of the cases. Pressure is an effective tuning parameter of structural properties and electronic correlations. Nevertheless, the ability to influence the magnetic phases should not be forgotten. We review experimental progress in the field of pressure-tuned magnetic interactions in candidate systems. Elaborating on the possibility of tuned quantum phase transitions, we further show that chemical or external pressure is a suitable parameter in these exotic states of matter. Full article

(This article belongs to the Special Issue Pressure-Induced Phase Transformations)

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9 pages, 2091 KiB

Open AccessEditor’s ChoiceReview

Mechanisms of Pressure-Induced Phase Transitions by Real-Time Laue Diffraction

by Dmitry Popov, Nenad Velisavljevic and Maddury Somayazulu

Crystals 2019, 9(12), 672; https://doi.org/10.3390/cryst9120672 - 14 Dec 2019

Cited by 8 | Viewed by 3315

Abstract

Synchrotron X-ray radiation Laue diffraction is a widely used diagnostic technique for characterizing the microstructure of materials. An exciting feature of this technique is that comparable numbers of reflections can be measured several orders of magnitude faster than using monochromatic methods. This makes [...] Read more.

Synchrotron X-ray radiation Laue diffraction is a widely used diagnostic technique for characterizing the microstructure of materials. An exciting feature of this technique is that comparable numbers of reflections can be measured several orders of magnitude faster than using monochromatic methods. This makes polychromatic beam diffraction a powerful tool for time-resolved microstructural studies, critical for understanding pressure-induced phase transition mechanisms, by in situ and in operando measurements. The current status of this technique, including experimental routines and data analysis, is presented along with some case studies. The new experimental setup at the High-Pressure Collaborative Access Team (HPCAT) facility at the Advanced Photon Source, specifically dedicated for in situ and in operando microstructural studies by Laue diffraction under high pressure, is presented. Full article

(This article belongs to the Special Issue Pressure-Induced Phase Transformations)

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32 pages, 1764 KiB

Open AccessEditor’s ChoiceReview

Pressure-Induced Phase Transitions in Sesquioxides

by Francisco Javier Manjón, Juan Angel Sans, Jordi Ibáñez and André Luis de Jesús Pereira

Crystals 2019, 9(12), 630; https://doi.org/10.3390/cryst9120630 - 28 Nov 2019

Cited by 21 | Viewed by 5274

Abstract

Pressure is an important thermodynamic parameter, allowing the increase of matter density by reducing interatomic distances that result in a change of interatomic interactions. In this context, the long range in which pressure can be changed (over six orders of magnitude with respect [...] Read more.

Pressure is an important thermodynamic parameter, allowing the increase of matter density by reducing interatomic distances that result in a change of interatomic interactions. In this context, the long range in which pressure can be changed (over six orders of magnitude with respect to room pressure) may induce structural changes at a much larger extent than those found by changing temperature or chemical composition. In this article, we review the pressure-induced phase transitions of most sesquioxides, i.e., A₂O₃ compounds. Sesquioxides constitute a big subfamily of ABO₃ compounds, due to their large diversity of chemical compositions. They are very important for Earth and Materials Sciences, thanks to their presence in our planet’s crust and mantle, and their wide variety of technological applications. Recent discoveries, hot spots, controversial questions, and future directions of research are highlighted. Full article

(This article belongs to the Special Issue Pressure-Induced Phase Transformations)

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19 pages, 5362 KiB

Open AccessEditor’s ChoiceReview

Towards a Germanium and Silicon Laser: The History and the Present

by Ivan Pelant and Kateřina Kůsová

Crystals 2019, 9(12), 624; https://doi.org/10.3390/cryst9120624 - 27 Nov 2019

Cited by 7 | Viewed by 5862

Abstract

Various theoretical as well as empirical considerations about how to achieve lasing between the conduction and valence bands in indirect band gap semiconductors (germanium and silicon) are reviewed, starting from the dawn of the laser epoch in the beginning of the sixties. While [...] Read more.

Various theoretical as well as empirical considerations about how to achieve lasing between the conduction and valence bands in indirect band gap semiconductors (germanium and silicon) are reviewed, starting from the dawn of the laser epoch in the beginning of the sixties. While in Ge the room-temperature lasing under electrical pum** has recently been achieved, in Si this objective remains still illusory. The necessity of applying a slightly different approach in Si as opposed to Ge is stressed. Recent advances in the field are discussed, based in particular on light-emitting Si quantum dots. Full article

(This article belongs to the Special Issue Light-Emittting Silicon Nanostructures)

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37 pages, 9722 KiB

Open AccessEditor’s ChoiceReview

Raman Scattering in Non-Stoichiometric Lithium Niobate Crystals with a Low Photorefractive Effect

by Nikolay Sidorov, Mikhail Palatnikov and Alexandra Kadetova

Crystals 2019, 9(10), 535; https://doi.org/10.3390/cryst9100535 - 17 Oct 2019

Cited by 14 | Viewed by 4288

Abstract

Raman spectra of lithium niobate single crystals strongly doped by zinc and magnesium, it has been established, contain low-intense bands with frequencies 209, 230, 298, 694, and 880 cm⁻¹. Ab ignition calculations fail to attribute these bands to fundamental vibrations of [...] Read more.

Raman spectra of lithium niobate single crystals strongly doped by zinc and magnesium, it has been established, contain low-intense bands with frequencies 209, 230, 298, 694, and 880 cm⁻¹. Ab ignition calculations fail to attribute these bands to fundamental vibrations of A₂ symmetry type unambiguously. Such vibrations are prohibited by the selection rules in the space group C_3V⁶ (R3c). Ab initio calculations also proved that low-intense “extra” bands with frequencies 104 and 119 cm⁻¹ definitely do not correspond to vibrations of A₂ symmetry type. We have paid special attention to these extra bands that appear in LiNbO₃ single crystals Raman spectra despite the fact that they are prohibited by the selection rules. In order to do so, we have studied a number of lithium niobate single crystals, both nominally pure and doped, by Raman spectroscopy. We have assumed that some “extra” bands correspond to two-particle states of acoustic phonons with a total wave vector equal to zero. We have also detected a Zn concentration area (0.05–0.94 mol.% ZnO in a crystal) where doped crystal structure is more ordered: The order of alternation of the main, do** cations, and vacancies along the polar axis is increased, and oxygen octahedra are less distorted. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystals)

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17 pages, 5395 KiB

Open AccessEditor’s ChoiceArticle

LED as Transmitter and Receiver of Light: A Simple Tool to Demonstration Photoelectric Effect

by Giuseppe Schirripa Spagnolo, Fabio Leccese and Mariagrazia Leccisi

Crystals 2019, 9(10), 531; https://doi.org/10.3390/cryst9100531 - 15 Oct 2019

Cited by 19 | Viewed by 15169

Abstract

The experimental observations of the photoelectric effect show the properties of quantum mechanics of the electromagnetic field. For this reason, this important effect is commonly used as an introductory topic for the study of quantum physics. The “classical” demonstration of the photoelectric effect [...] Read more.

The experimental observations of the photoelectric effect show the properties of quantum mechanics of the electromagnetic field. For this reason, this important effect is commonly used as an introductory topic for the study of quantum physics. The “classical” demonstration of the photoelectric effect is very incisive; unfortunately, the experimental apparatus is not cheap and easy to realize. The typical use of LEDs is as light emitters, but they can be used even as photosensors and, in this case, they are sensitive to wavelengths equal to or shorter than the predominant wavelength it emits. Furthermore, a LED used as detector is sensitive to wavelengths equal to or shorter than the predominant wavelength it emits. This ability of LEDs offers the possibility of develo** a simple tool able to demonstrate the photoelectric effect. This paper describes the realization of an economic, simple, easy and safe system to use for the experimental demonstration of the photoelectric effect, based on the LED to LED structure. The paper has educational purposes, oriented towards laboratory teaching activities. Full article

(This article belongs to the Special Issue Recent Advances in Light-Emitting Diodes (LEDs))

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14 pages, 2631 KiB

Open AccessEditor’s ChoiceArticle

Bifurcated Triel Bonds—Hydrides and Halides of 1,2-Bis(Dichloroboryl)Benzene and 1,8-Bis(Dichloroboryl)Naphthalene

by Sławomir J. Grabowski

Crystals 2019, 9(10), 503; https://doi.org/10.3390/cryst9100503 - 27 Sep 2019

Cited by 17 | Viewed by 2920

Abstract

MP2/aug-cc-pVTZ calculations were performed on hydrides, fluorides, and chlorides of 1,8-bis(dichloroboryl)naphthalene and 1,2-bis(dichloroboryl)benzene. The theoretical analysis of BHB⁻, BFB⁻, and BClB⁻ arrangements occurring in these complexes and classified as bifurcated triel bonds was partly based on decomposition of [...] Read more.

MP2/aug-cc-pVTZ calculations were performed on hydrides, fluorides, and chlorides of 1,8-bis(dichloroboryl)naphthalene and 1,2-bis(dichloroboryl)benzene. The theoretical analysis of BHB⁻, BFB⁻, and BClB⁻ arrangements occurring in these complexes and classified as bifurcated triel bonds was partly based on decomposition of the energy of interaction. The latter was carried out for structures optimized using the DFT method. The complexes analyzed were characterized by a partly covalent character of the links to the hydride and halide anions; these anions strongly influenced the geometry of the complexes. The boron centers’ links for the neutral 1,8-bis(dichloroboryl)naphthalene and 1,2-bis(dichloroboryl)benzene molecules were characterized by approximately trigonal and planar configurations, while for anionic complexes, tetrahedral configurations were observed. The crystal structures of compounds related to species calculated here were found in the Cambridge Structural Database (CSD). Full article

(This article belongs to the Special Issue Experimental and Theoretical Electron-Density Study of Crystalline Materials)

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22 pages, 5747 KiB

Open AccessEditor’s ChoiceReview

From Molecules to Carbon Materials—High Pressure Induced Polymerization and Bonding Mechanisms of Unsaturated Compounds

by **n Yang, Xuan Wang, Yida Wang, Kuo Li and Haiyan Zheng

Crystals 2019, 9(10), 490; https://doi.org/10.3390/cryst9100490 - 24 Sep 2019

Cited by 18 | Viewed by 4636

Abstract

With the development of high-pressure apparatus, in situ characterization methods and theoretical calculations, high-pressure technology becomes a more and more important method to synthesize new compounds with unusual structures and properties. By compressing compounds containing unsaturated carbon atoms, novel poly-ionic polymers, graphanes and [...] Read more.

With the development of high-pressure apparatus, in situ characterization methods and theoretical calculations, high-pressure technology becomes a more and more important method to synthesize new compounds with unusual structures and properties. By compressing compounds containing unsaturated carbon atoms, novel poly-ionic polymers, graphanes and carbon nanothreads were obtained. Their compositions and structures were carefully studied by combining multiple cutting-edge technologies, like the in situ high-pressure X-ray and neutron diffraction, transmission electron microscopy, pair distribution function, solid-state nuclear magnetic resonance and gas chromatography-mass spectroscopy. The reaction mechanisms were investigated based on the crystal structure at the reaction threshold pressure (the pressure just before the reaction taking place), the long-range and short-range structure of the product, molecular structure of the intermediates, as well as the theoretical calculation. In this review, we will summarize the synthesis of carbon materials by compressing the unsaturated compounds and its reaction characteristics under extreme conditions. The topochemical reaction mechanism and related characterization methods of the molecular system will be highlighted. This review will provide a reference for designing chemical reaction and exploring novel carbon materials under high-pressure condition. Full article

(This article belongs to the Special Issue High Pressure Synthesis in Crystalline Materials)

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23 pages, 10591 KiB

Open AccessEditor’s ChoiceReview

Polaronic Emergent Phases in Manganite-based Heterostructures

by Vasily Moshnyaga and Konrad Samwer

Crystals 2019, 9(10), 489; https://doi.org/10.3390/cryst9100489 - 22 Sep 2019

Cited by 4 | Viewed by 3846

Abstract

Transition metal functional oxides, e.g., perovskite manganites, with strong electron, spin and lattice correlations, are well-known for different phase transitions and field-induced colossal effects at the phase transition. Recently, the interfaces between dissimilar perovskites were shown to be a promising concept for the [...] Read more.

Transition metal functional oxides, e.g., perovskite manganites, with strong electron, spin and lattice correlations, are well-known for different phase transitions and field-induced colossal effects at the phase transition. Recently, the interfaces between dissimilar perovskites were shown to be a promising concept for the search of emerging phases with novel functionalities. We demonstrate that the properties of manganite films are effectively controlled by low dimensional emerging phases at intrinsic and extrinsic interfaces and appeared as a result of symmetry breaking. The examples include correlated Jahn–Teller polarons in the phase-separated (La_1−yPr_y)_0.7Ca_0.3MnO₃, electron-rich Jahn–Teller-distorted surface or “dead” layer in La_0.7Sr_0.3MnO₃, electric-field-induced healing of “dead” layer as an origin of resistance switching effect, and high-T_C ferromagnetic emerging phase at the SrMnO₃/LaMnO₃ interface in superlattices. These 2D polaronic phases with short-range electron, spin, and lattice reconstructions could be extremely sensitive to external fields, thus, providing a rational explanation of colossal effects in perovskite manganites. Full article

(This article belongs to the Special Issue Electronic Phenomena of Transition Metal Oxides)

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17 pages, 1366 KiB

Open AccessEditor’s ChoiceArticle

Critical Review of Scintillating Crystals for Neutron Detection

by Michał J. Cieślak, Kelum A. A. Gamage and Robert Glover

Crystals 2019, 9(9), 480; https://doi.org/10.3390/cryst9090480 - 13 Sep 2019

Cited by 62 | Viewed by 9715

Abstract

There exists an ongoing need to develop and improve methods of detecting radioactive materials. As each radioactive isotope leaves a unique mark in a form of the particles it emits, new materials capable of detecting and measuring these particles are constantly sought. Neutrons [...] Read more.

There exists an ongoing need to develop and improve methods of detecting radioactive materials. As each radioactive isotope leaves a unique mark in a form of the particles it emits, new materials capable of detecting and measuring these particles are constantly sought. Neutrons and their detectors play a significant role in areas such as nuclear power generation, nuclear decommissioning and decontamination, border security, nuclear proliferation and nuclear medicine. Owing to the complexity of their detection, as well as scarcity of ³He, which has historically been the preferred choice for neutron detection in many application fields, new sensitive materials are sought. Organic and inorganic scintillating crystals have been recognised as particularly good alternatives, and as such systems that utilise them are increasingly common. As they allow investigation of the neutron energy spectra, greater information about the radioactive source can be inferred. Therefore, in this article, an extensive review of scintillating crystals used for neutron detection is presented. By describing the history of scintillating crystals and discussing changes that occurred in their use and development of methods for radiation detection, the authors present a comprehensive overview of the current situation. Supported by a practical example, possible future directions of the research area are also presented. Full article

(This article belongs to the Special Issue Scintillator Crystals: Structure, Characterization and Models for Better Performances)

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13 pages, 3227 KiB

Open AccessEditor’s ChoiceArticle

Direct Growth of Flower-Shaped ZnO Nanostructures on FTO Substrate for Dye-Sensitized Solar Cells

by Ahmad Umar, Mohammad Shaheer Akhtar, Tubia Almas, Ahmed Abdulbaqi Ibrahim, Mohammed Sultan Al-Assiri, Yoshitake Masuda, Qazi Inamur Rahman and Sotirios Baskoutas

Crystals 2019, 9(8), 405; https://doi.org/10.3390/cryst9080405 - 4 Aug 2019

Cited by 18 | Viewed by 4886

Abstract

The proposed work reports that ZnO nanoflowers were grown on fluorine-doped tin oxide (FTO) substrates via a solution process at low temperature. The high purity and well-crystalline behavior of ZnO nanoflowers were established by X-ray diffraction. The morphological characteristics of ZnO nanoflowers were [...] Read more.

The proposed work reports that ZnO nanoflowers were grown on fluorine-doped tin oxide (FTO) substrates via a solution process at low temperature. The high purity and well-crystalline behavior of ZnO nanoflowers were established by X-ray diffraction. The morphological characteristics of ZnO nanoflowers were clearly revealed that the grown flower structures were in high density with 3D floral structure comprising of small rods assembled as petals. Using UV absorption and Raman spectroscopy, the optical and structural properties of the ZnO nanoflowers were studied. The photoelectrochemical properties of the ZnO nanoflowers were studied by utilizing as a photoanode for the manufacture of dye-sensitized solar cells (DSSCs). The fabricated DSSC with ZnO nanoflowers photoanode attained reasonable overall conversion efficiency of ~1.40% and a short-circuit current density (J_SC) of ~4.22 mA cm⁻² with an open circuit voltage (V_OC) of 0.615 V and a fill factor (FF) of ~0.54. ZnO nanostructures have given rise to possible utilization as an inexpensive and efficient photoanode materials for DSSCs. Full article

(This article belongs to the Special Issue Zinc Oxide Nanomaterials and Based Devices)

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17 pages, 5407 KiB

Open AccessEditor’s ChoiceReview

Quality Control and Structural Assessment of Anisotropic Scintillating Crystals

by Luigi Montalto, Pier Paolo Natali, Lorenzo Scalise, Nicola Paone, Fabrizio Davì, Daniele Rinaldi, Gianni Barucca and Paolo Mengucci

Crystals 2019, 9(7), 376; https://doi.org/10.3390/cryst9070376 - 23 Jul 2019

Cited by 9 | Viewed by 3926

Abstract

Nowadays, radiation detectors based on scintillating crystals are used in many different fields of science like medicine, aerospace, high-energy physics, and security. The scintillating crystals are the core elements of these devices; by converting high-energy radiation into visible photons, they produce optical signals [...] Read more.

Nowadays, radiation detectors based on scintillating crystals are used in many different fields of science like medicine, aerospace, high-energy physics, and security. The scintillating crystals are the core elements of these devices; by converting high-energy radiation into visible photons, they produce optical signals that can be detected and analyzed. Structural and surface conditions, defects, and residual stress states play a crucial role in their operating performance in terms of light production, transport, and extraction. Industrial production of such crystalline materials is a complex process that requires sensing, in-line and off-line, for material characterization and process control to properly tune the production parameters. Indeed, the scintillators’ quality must be accurately assessed during their manufacture in order to prevent malfunction and failures at each level of the chain, optimizing the production and utilization costs. This paper presents an overview of the techniques used, at various stages, across the crystal production process, to assess the quality and structural condition of anisotropic scintillating crystals. Different inspection techniques (XRD, SEM, EDX, and TEM) and the non-invasive photoelasticity-based methods for residual stress detection, such as laser conoscopy and sphenoscopy, are presented. The use of XRD, SEM, EDX, and TEM analytical methods offers detailed structural and morphological information. Conoscopy and sphenoscopy offer the advantages of fast and non-invasive measurement suitable for the inspection of the whole crystal quality. These techniques, based on different measurement methods and models, provide different information that can be cross-correlated to obtain a complete characterization of the scintillating crystals. Inspection methods will be analyzed and compared to the present state of the art. Full article

(This article belongs to the Special Issue Scintillator Crystals: Structure, Characterization and Models for Better Performances)

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43 pages, 7846 KiB

Open AccessEditor’s ChoiceReview

Layered Double Hydroxides: A Toolbox for Chemistry and Biology

by Giuseppe Arrabito, Aurelio Bonasera, Giuseppe Prestopino, Andrea Orsini, Alessio Mattoccia, Eugenio Martinelli, Bruno Pignataro and Pier Gianni Medaglia

Crystals 2019, 9(7), 361; https://doi.org/10.3390/cryst9070361 - 15 Jul 2019

Cited by 70 | Viewed by 19037

Abstract

Layered double hydroxides (LDHs) are an emergent class of biocompatible inorganic lamellar nanomaterials that have attracted significant research interest owing to their high surface-to-volume ratio, the capability to accumulate specific molecules, and the timely release to targets. Their unique properties have been employed [...] Read more.

Layered double hydroxides (LDHs) are an emergent class of biocompatible inorganic lamellar nanomaterials that have attracted significant research interest owing to their high surface-to-volume ratio, the capability to accumulate specific molecules, and the timely release to targets. Their unique properties have been employed for applications in organic catalysis, photocatalysis, sensors, drug delivery, and cell biology. Given the widespread contemporary interest in these topics, time-to-time it urges to review the recent progresses. This review aims to summarize the most recent cutting-edge reports appearing in the last years. It firstly focuses on the application of LDHs as catalysts in relevant chemical reactions and as photocatalysts for organic molecule degradation, water splitting reaction, CO₂ conversion, and reduction. Subsequently, the emerging role of these materials in biological applications is discussed, specifically focusing on their use as biosensors, DNA, RNA, and drug delivery, finally elucidating their suitability as contrast agents and for cellular differentiation. Concluding remarks and future prospects deal with future applications of LDHs, encouraging researches in better understanding the fundamental mechanisms involved in catalytic and photocatalytic processes, and the molecular pathways that are activated by the interaction of LDHs with cells in terms of both uptake mechanisms and nanotoxicology effects. Full article

(This article belongs to the Special Issue Layered Double Hydroxides)

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8 pages, 1858 KiB

Open AccessEditor’s ChoiceArticle

Optical Transport Properties of Graphene Surface Plasmon Polaritons in Mid-Infrared Band

by Yindi Wang, Hongxia Liu, Shulong Wang, Ming Cai and Lan Ma

Crystals 2019, 9(7), 354; https://doi.org/10.3390/cryst9070354 - 12 Jul 2019

Cited by 25 | Viewed by 3694

Abstract

The excellent transmission characteristics of graphene surface plasmon polaritons in mid-infrared band were analyzed and verified effectively through theoretical derivation and soft simulation in this paper. Meanwhile, a sandwich waveguide structure of dielectric–graphene–substrate–dielectric based on graphene surface plasmon polaritons (SPPs) was presented. Simulation [...] Read more.

The excellent transmission characteristics of graphene surface plasmon polaritons in mid-infrared band were analyzed and verified effectively through theoretical derivation and soft simulation in this paper. Meanwhile, a sandwich waveguide structure of dielectric–graphene–substrate–dielectric based on graphene surface plasmon polaritons (SPPs) was presented. Simulation results indicate that graphene SPPs show unique properties in the mid-infrared region including ultra-compact mode confinement and dynamic tunability, which allow these SPPs to overcome the defects of metal SPPs and traditional silicon-based optoelectronic devices. Thus, they can be used to manufacture subwavelength devices. The work in this paper lays a theoretical foundation for the application of graphene SPPs in the mid-infrared region. Full article

(This article belongs to the Special Issue Graphene Mechanics)

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14 pages, 3033 KiB

Open AccessEditor’s ChoiceArticle

The Fabrication of Calcium Alginate Beads as a Green Sorbent for Selective Recovery of Cu(Ⅱ) from Metal Mixtures

by Niannian Yang, Runkai Wang, Pinhua Rao, Lili Yan, Wenqi Zhang, **cheng Wang and Fei Chai

Crystals 2019, 9(5), 255; https://doi.org/10.3390/cryst9050255 - 17 May 2019

Cited by 60 | Viewed by 6136

Abstract

Calcium alginate (CA) beads as a green sorbent were easily fabricated in this study using sodium alginate crosslinking with CaCl₂, and the crosslinking pathway was the exchange between the sodium ion of α-L-guluronic acid and Ca(II). The experimental study was conducted [...] Read more.

Calcium alginate (CA) beads as a green sorbent were easily fabricated in this study using sodium alginate crosslinking with CaCl₂, and the crosslinking pathway was the exchange between the sodium ion of α-L-guluronic acid and Ca(II). The experimental study was conducted on Cu(II), Cd(II), Ni(II) and Zn(II) as the model heavy metals and the concentration was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The characterization and sorption behavior of the CA beads were analyzed in detail via using scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The adsorption experiments demonstrated that the CA beads exhibited a high removal efficiency for the selective adsorption of Cu(II) from the tetra metallic mixture solution and an excellent adsorption capacity of the heavy metals separately. According to the isotherm studies, the maximum uptake of Cu(II) could reach 107.53 mg/g, which was significantly higher than the other three heavy metal ions in the tetra metallic mixture solution. Additionally, after five cycles of adsorption and desorption, the uptake rate of Cu(II) on CA beads was maintained at 92%. According to the properties mentioned above, this material was assumed to be applied to reduce heavy metal pollution or recover valuable metals from waste water. Full article

(This article belongs to the Special Issue Layered Double Hydroxides)

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15 pages, 1497 KiB

Open AccessEditor’s ChoiceArticle

Van der Waals Density Functional Theory vdW-DFq for Semihard Materials

by Qing Peng, Guangyu Wang, Gui-Rong Liu and Suvranu De

Crystals 2019, 9(5), 243; https://doi.org/10.3390/cryst9050243 - 8 May 2019

Cited by 22 | Viewed by 5119

Abstract

There are a large number of materials with mild stiffness, which are not as soft as tissues and not as strong as metals. These semihard materials include energetic materials, molecular crystals, layered materials, and van der Waals crystals. The integrity and mechanical stability [...] Read more.

There are a large number of materials with mild stiffness, which are not as soft as tissues and not as strong as metals. These semihard materials include energetic materials, molecular crystals, layered materials, and van der Waals crystals. The integrity and mechanical stability are mainly determined by the interactions between instantaneously induced dipoles, the so called London dispersion force or van der Waals force. It is challenging to accurately model the structural and mechanical properties of these semihard materials in the frame of density functional theory where the non-local correlation functionals are not well known. Here, we propose a van der Waals density functional named vdW-DFq to accurately model the density and geometry of semihard materials. Using

β

-cyclotetramethylene tetranitramine as a prototype, we adjust the enhancement factor of the exchange energy functional with generalized gradient approximations. We find this method to be simple and robust over a wide tuning range when calibrating the functional on-demand with experimental data. With a calibrated value

q = 1.05

, the proposed vdW-DFq method shows good performance in predicting the geometries of 11 common energetic material molecular crystals and three typical layered van der Waals crystals. This success could be attributed to the similar electronic charge density gradients, suggesting a wide use in modeling semihard materials. This method could be useful in develo** non-empirical density functional theories for semihard and soft materials. Full article

(This article belongs to the Special Issue First-Principles Prediction of Structures and Properties in Crystals)

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11 pages, 4319 KiB

Open AccessEditor’s ChoiceArticle

Dielectric and Piezoelectric Properties of Textured Lead-Free Na_0.5Bi_0.5TiO₃-Based Ceramics

by Nannan Dong, **aoyi Gao, Fangquan **a, Hanxing Liu, Hua Hao and Shujun Zhang

Crystals 2019, 9(4), 206; https://doi.org/10.3390/cryst9040206 - 14 Apr 2019

Cited by 24 | Viewed by 3950

Abstract

This work provides a comparative study of the dielectric and piezoelectric properties of randomly oriented and textured 0.88Na_0.5Bi_0.5TiO₃-0.08K_0.5Bi_0.5TiO₃-0.04BaTiO₃ (88NBT) ceramics. Textured ceramics were fabricated by template grain growth (TGG) method [...] Read more.

This work provides a comparative study of the dielectric and piezoelectric properties of randomly oriented and textured 0.88Na_0.5Bi_0.5TiO₃-0.08K_0.5Bi_0.5TiO₃-0.04BaTiO₃ (88NBT) ceramics. Textured ceramics were fabricated by template grain growth (TGG) method using NaNbO₃ (NN) for templates. For textured ceramics with 4 wt% NN templates, a Lotgering factor of 96% and piezoelectric coefficient d₃₃ of 185 pC/N were obtained. Compared to the randomly oriented ceramics, textured ceramics show lower strain hysteresis (H = 7.6%), higher unipolar strain of 0.041% with corresponding large signal piezoelectric coefficient d₃₃^* of 200 pm/V at applied field of 2 kV/mm. This enhancement can be explained by the grain orientation along <001> direction by texturing, where an engineered domain configuration is formed after polarization, leading to decreased hysteresis and increased piezoelectric property. Full article

(This article belongs to the Section Crystalline Materials)

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12 pages, 604 KiB

Open AccessEditor’s ChoiceReview

Prospective of (BaCa)(ZrTi)O₃ Lead-free Piezoelectric Ceramics

by Wenfeng Liu, Lu Cheng and Shengtao Li

Crystals 2019, 9(3), 179; https://doi.org/10.3390/cryst9030179 - 26 Mar 2019

Cited by 27 | Viewed by 4997

Abstract

Piezoelectric ceramics is a functional material that can convert mechanical energy into electrical energy and vice versa. It can find wide applications ranging from our daily life to high-end techniques and dominates a billion-dollar market. For half a century, the working horse of [...] Read more.

Piezoelectric ceramics is a functional material that can convert mechanical energy into electrical energy and vice versa. It can find wide applications ranging from our daily life to high-end techniques and dominates a billion-dollar market. For half a century, the working horse of the field has been the polycrystalline PbZr_1−xTi_xO₃ (PZT), which is now globally resisted for containing the toxic element lead. In 2009, our group discovered a non-Pb piezoelectric material, (BaCa)(ZrTi)O₃ ceramics (BZT-BCT), which exhibits an ultrahigh piezoelectric coefficient d₃₃ of 560–620 pC/N. This result brought extensive interest in the research field and important consequences for the piezoelectric industry that has relied on PZT. In the present paper, we review the recent progress, both experimental and theoretical, in the BZT-BCT ceramics. Full article

(This article belongs to the Special Issue Synthesis and Characterization of Ferroelectrics)

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8 pages, 2170 KiB

Open AccessEditor’s ChoiceCommunication

Hybrid Biomimetic Materials from Silica/Carbonate Biomorphs

by Julian Opel, Niklas Unglaube, Melissa Wörner, Matthias Kellermeier, Helmut Cölfen and Juan-Manuel García-Ruiz

Crystals 2019, 9(3), 157; https://doi.org/10.3390/cryst9030157 - 18 Mar 2019

Cited by 10 | Viewed by 3970

Abstract

The formation of a polymer protection layer around fragile mineral architectures ensures that structures stay intact even after treatments that would normally destroy them going along with a total loss of textural information. Here we present a strategy to preserve the shape of [...] Read more.

The formation of a polymer protection layer around fragile mineral architectures ensures that structures stay intact even after treatments that would normally destroy them going along with a total loss of textural information. Here we present a strategy to preserve the shape of silica-carbonate biomorphs with polymers. This method converts non-hybrid inorganic-inorganic composite materials such a silica/carbonate biomorphs into hybrid organic/carbonate composite materials similar to biominerals. Full article

(This article belongs to the Special Issue Biological Crystallization)

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49 pages, 9954 KiB

Open AccessEditor’s ChoiceReview

Crystallochemical Design of Huntite-Family Compounds

by Galina M. Kuz’micheva, Irina A. Kaurova, Victor B. Rybakov and Vadim V. Podbel’skiy

Crystals 2019, 9(2), 100; https://doi.org/10.3390/cryst9020100 - 15 Feb 2019

Cited by 24 | Viewed by 5031

Abstract

Huntite-family nominally-pure and activated/co-activated LnM₃(BO₃)₄ (Ln = La–Lu, Y; M = Al, Fe, Cr, Ga, Sc) compounds and their-based solid solutions are promising materials for lasers, nonlinear optics, spintronics, and photonics, which are characterized by multifunctional properties [...] Read more.

Huntite-family nominally-pure and activated/co-activated LnM₃(BO₃)₄ (Ln = La–Lu, Y; M = Al, Fe, Cr, Ga, Sc) compounds and their-based solid solutions are promising materials for lasers, nonlinear optics, spintronics, and photonics, which are characterized by multifunctional properties depending on a composition and crystal structure. The purpose of the work is to establish stability regions for the rare-earth orthoborates in crystallochemical coordinates (sizes of Ln and M ions) based on their real compositions and space symmetry depending on thermodynamic, kinetic, and crystallochemical factors. The use of diffraction structural techniques to study single crystals with a detailed analysis of diffraction patterns, refinement of crystallographic site occupancies (real composition), and determination of structure–composition correlations is the most efficient and effective option to achieve the purpose. This approach is applied and shown primarily for the rare-earth scandium borates having interesting structural features compared with the other orthoborates. Visualization of structures allowed to establish features of formation of phases with different compositions, to classify and systematize huntite-family compounds using crystallochemical concepts (structure and superstructure, ordering and disordering, isostructural and isotype compounds) and phenomena (isomorphism, morphotropism, polymorphism, polytypism). Particular attention is paid to methods and conditions for crystal growth, affecting a crystal real composition and symmetry. A critical analysis of literature data made it possible to formulate unsolved problems in materials science of rare-earth orthoborates, mainly scandium borates, which are distinguished by an ability to form internal and substitutional (Ln and Sc atoms), unlimited and limited solid solutions depending on the geometric factor. Full article

(This article belongs to the Special Issue Crystal Growth of Multifunctional Borates and Related Materials)

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16 pages, 3290 KiB

Open AccessEditor’s ChoiceReview

Recent Advances on Carrier and Exciton Self-Trap** in Strontium Titanate: Understanding the Luminescence Emissions

by Miguel L. Crespillo, Joseph T. Graham, Fernando Agulló-López, Yanwen Zhang and William J. Weber

Crystals 2019, 9(2), 95; https://doi.org/10.3390/cryst9020095 - 13 Feb 2019

Cited by 33 | Viewed by 5868

Abstract

An up-to-date review on recent results for self-trap** of free electrons and holes, as well as excitons, in strontium titanate (STO), which gives rise to small polarons and self-trapped excitons (STEs) is presented. Special attention is paid to the role of carrier and [...] Read more.

An up-to-date review on recent results for self-trap** of free electrons and holes, as well as excitons, in strontium titanate (STO), which gives rise to small polarons and self-trapped excitons (STEs) is presented. Special attention is paid to the role of carrier and exciton self-trap** on the luminescence emissions under a variety of excitation sources with special emphasis on experiments with laser pulses and energetic ion-beams. In spite of the extensive research effort, a definitive identification of such localized states, as well as a suitable understanding of their operative light emission mechanisms, has remained lacking or controversial. However, promising advances have been recently achieved and are the objective of the present review. In particular, significant theoretical advances in the understanding of electron and hole self-trap** are discussed. Also, relevant experimental advances in the kinetics of light emission associated with electron-hole recombination have been obtained through time-resolved experiments using picosecond (ps) laser pulses. The luminescence emission mechanisms and the light decay processes from the self-trapped excitons are also reviewed. Recent results suggest that the blue emission at 2.8 eV, often associated with oxygen vacancies, is related to a transition from unbound conduction levels to the ground singlet state of the STE. The stabilization of small electron polarons by oxygen vacancies and its connection with luminescence emission are discussed in detail. Through ion-beam irradiation experiments, it has recently been established that the electrons associated with the vacancy constitute electron polaron states (Ti³⁺) trapped in the close vicinity of the empty oxygen sites. These experimental results have allowed for the optical identification of the oxygen vacancy center through a red luminescence emission centered at 2.0 eV. Ab-initio calculations have provided strong support for those experimental findings. Finally, the use of Cr-doped STO has offered a way to monitor the interplay between the chromium centers and oxygen vacancies as trap** sites for the electron and hole partners resulting from the electronic excitation. Full article

(This article belongs to the Special Issue Advances in Structural and Compositional Characterization for the Development of Wide Bandgap Semiconductors)

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29 pages, 9219 KiB

Open AccessEditor’s ChoiceReview

Inorganic, Organic, and Perovskite Halides with Nanotechnology for High–Light Yield X- and γ-ray Scintillators

by Francesco Maddalena, Liliana Tjahjana, Aozhen **e, Arramel, Shuwen Zeng, Hong Wang, Philippe Coquet, Winicjusz Drozdowski, Christophe Dujardin, Cuong Dang and Muhammad Danang Birowosuto

Crystals 2019, 9(2), 88; https://doi.org/10.3390/cryst9020088 - 8 Feb 2019

Cited by 160 | Viewed by 17049

Abstract

Trends in scintillators that are used in many applications, such as medical imaging, security, oil-logging, high energy physics and non-destructive inspections are reviewed. First, we address traditional inorganic and organic scintillators with respect of limitation in the scintillation light yields and lifetimes. The [...] Read more.

Trends in scintillators that are used in many applications, such as medical imaging, security, oil-logging, high energy physics and non-destructive inspections are reviewed. First, we address traditional inorganic and organic scintillators with respect of limitation in the scintillation light yields and lifetimes. The combination of high–light yield and fast response can be found in Ce

^{3 +}

, Pr

^{3 +}

and Nd

^{3 +}

lanthanide-doped scintillators while the maximum light yield conversion of 100,000 photons/MeV can be found in Eu

^{3 +}

doped SrI

_{2}

. However, the fabrication of those lanthanide-doped scintillators is inefficient and expensive as it requires high-temperature furnaces. A self-grown single crystal using solution processes is already introduced in perovskite photovoltaic technology and it can be the key for low-cost scintillators. A novel class of materials in scintillation includes lead halide perovskites. These materials were explored decades ago due to the large X-ray absorption cross section. However, lately lead halide perovskites have become a focus of interest due to recently reported very high photoluminescence quantum yield and light yield conversion at low temperatures. In principle, 150,000–300,000 photons/MeV light yields can be proportional to the small energy bandgap of these materials, which is below 2 eV. Finally, we discuss the extraction efficiency improvements through the fabrication of the nanostructure in scintillators, which can be implemented in perovskite materials. The recent technology involving quantum dots and nanocrystals may also improve light conversion in perovskite scintillators. Full article

(This article belongs to the Special Issue Scintillator Crystals: Structure, Characterization and Models for Better Performances)

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18 pages, 6120 KiB

Open AccessEditor’s ChoiceArticle

Critical Evaluation of Organic Thin-Film Transistor Models

by Markus Krammer, James W. Borchert, Andreas Petritz, Esther Karner-Petritz, Gerburg Schider, Barbara Stadlober, Hagen Klauk and Karin Zojer

Crystals 2019, 9(2), 85; https://doi.org/10.3390/cryst9020085 - 6 Feb 2019

Cited by 20 | Viewed by 5796

Abstract

The thin-film transistor (TFT) is a popular tool for determining the charge-carrier mobility in semiconductors, as the mobility (and other transistor parameters, such as the contact resistances) can be conveniently extracted from its measured current-voltage characteristics. However, the accuracy of the extracted parameters [...] Read more.

The thin-film transistor (TFT) is a popular tool for determining the charge-carrier mobility in semiconductors, as the mobility (and other transistor parameters, such as the contact resistances) can be conveniently extracted from its measured current-voltage characteristics. However, the accuracy of the extracted parameters is quite limited, because their values depend on the extraction technique and on the validity of the underlying transistor model. We propose here a new approach for validating to what extent a chosen transistor model is able to predict correctly the transistor operation. In the two-step fitting approach we have developed, we analyze the measured current-voltage characteristics of a series of TFTs with different channel lengths. In the first step, the transistor parameters are extracted from each individual transistor by fitting the output and transfer characteristics to the transistor model. In the second step, we check whether the channel-length dependence of the extracted parameters is consistent with the underlying model. We present results obtained from organic TFTs fabricated in two different laboratories using two different device architectures, three different organic semiconductors and five different materials combinations for the source and drain contacts. For each set of TFTs, our approach reveals that the state-of-the-art transistor models fail to reproduce correctly the channel-length-dependence of the transistor parameters. Our approach suggests that conventional transistor models require improvements in terms of the charge-carrier-density dependence of the mobility and/or in terms of the consideration of uncompensated charges in the carrier-accumulation channel. Full article

(This article belongs to the Special Issue Thin Film Transistor)

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9 pages, 3228 KiB

Open AccessEditor’s ChoiceArticle

Liquid-Phase Epitaxial Growth and Characterization of Nd:YAl₃(BO₃)₄ Optical Waveguides

by Yi Lu, Peter Dekker and Judith M. Dawes

Crystals 2019, 9(2), 79; https://doi.org/10.3390/cryst9020079 - 1 Feb 2019

Cited by 4 | Viewed by 3547

Abstract

We investigated the fabrication of neodymium doped thin film optical waveguide-based devices as potential active sources for planar integrated optics. Liquid-phase epitaxial growth was used to fabricate neodymium-doped yttrium aluminum borate films on compatible lattice-matched, un-doped yttrium aluminum borate substrates. We observed the [...] Read more.

We investigated the fabrication of neodymium doped thin film optical waveguide-based devices as potential active sources for planar integrated optics. Liquid-phase epitaxial growth was used to fabricate neodymium-doped yttrium aluminum borate films on compatible lattice-matched, un-doped yttrium aluminum borate substrates. We observed the refractive index contrast of the doped and un-doped crystal layers via differential interference contrast microscopy. In addition, characterization by X-ray powder diffraction, optical absorption and luminescence spectra demonstrated the crystal quality, uniformity and optical guiding of the resulting thin films. Full article

(This article belongs to the Special Issue Crystal Growth of Multifunctional Borates and Related Materials)

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18 pages, 18471 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Emerging Perovskite Nanocrystals-Enhanced Solid-State Lighting and Liquid-Crystal Displays

by Ziqian He, Caicai Zhang, Yajie Dong and Shin-Tson Wu

Crystals 2019, 9(2), 59; https://doi.org/10.3390/cryst9020059 - 22 Jan 2019

Cited by 52 | Viewed by 8211

Abstract

Recent advances in perovskite nanocrystals-enhanced solid-state lighting (SSL) and liquid-crystal displays (LCDs) are reviewed. We first discuss the development, optical properties, and stability issue of materials, and then we evaluate the performance of SSL and LCDs with perovskite downconverters adopted. In SSL performance [...] Read more.

Recent advances in perovskite nanocrystals-enhanced solid-state lighting (SSL) and liquid-crystal displays (LCDs) are reviewed. We first discuss the development, optical properties, and stability issue of materials, and then we evaluate the performance of SSL and LCDs with perovskite downconverters adopted. In SSL performance evaluation, we investigate the fitting-curve effect in calculations and optimizations where simple Gaussian fitting and precise fitting are compared in detail, and we further optimize for highly efficient, good color-rendering, and human-healthy SSL sources. For LCD performance evaluation, we study the intrinsic tradeoffs between total light efficiency and color gamut coverage. Through optimizations using real line shapes, Rec. 2020 standard coverage as large as 92.8% can be achieved through hybrid integration. Finally, we briefly discuss two future challenges: materials development and device integration. We believe the emerging perovskite nanocrystals are highly promising for next-generation SSL and LCDs. Full article

(This article belongs to the Special Issue Advanced LED Solid-State Lighting Optics)

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18 pages, 3517 KiB

Open AccessEditor’s ChoiceArticle

Spatio-temporal Investigations of the Incomplete Spin Transition in a Single Crystal of [Fe(2-pytrz)₂{Pt(CN)₄}]·3H₂O: Experiment and Theory

by Houcem Fourati, Guillaume Bouchez, Miguel Paez-Espejo, Smail Triki and Kamel Boukheddaden

Crystals 2019, 9(1), 46; https://doi.org/10.3390/cryst9010046 - 16 Jan 2019

Cited by 13 | Viewed by 3867

Abstract

Optical microscopy technique is used to investigate the thermal and the spatio-temporal properties of the spin-crossover single crystal [Fe(2-pytrz)

_{2}

{Pt(CN)

_{4}

}]·3H

_{2}

O, which exhibits a first-order spin transition from a full high-spin (HS) state at high temperature to an intermediate, [...] Read more.

Optical microscopy technique is used to investigate the thermal and the spatio-temporal properties of the spin-crossover single crystal [Fe(2-pytrz)

_{2}

{Pt(CN)

_{4}

}]·3H

_{2}

O, which exhibits a first-order spin transition from a full high-spin (HS) state at high temperature to an intermediate, high-spin low-spin (HS-LS) state, below 153 K, where only one of the two crystallographic Fe(II) centers switches from the HS to HS-LS state. In comparison with crystals undergoing a complete spin transition, the present transformation involves smaller volume changes at the transition, which helps to preserving the crystal’s integrity. By analyzing the spatio-temporal properties of this spin transition, we evidenced a direct correlation between the orientation and shape of HS/HS-LS domain wall with the crystal’s shape. Thanks to the small volume change accompanying this spin transition, the analysis of the experimental data by an anisotropic reaction-diffusion model becomes very relevant and leads to an excellent agreement with the experimental observations. Full article

(This article belongs to the Special Issue Synthesis and Applications of New Spin Crossover Compounds)

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10 pages, 3859 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Tripling the Optical Efficiency of Color-Converted Micro-LED Displays with Funnel-Tube Array

by Fangwang Gou, En-Lin Hsiang, Guanjun Tan, Yi-Fen Lan, Cheng-Yeh Tsai and Shin-Tson Wu

Crystals 2019, 9(1), 39; https://doi.org/10.3390/cryst9010039 - 14 Jan 2019

Cited by 50 | Viewed by 10095

Abstract

Color-converted micro-LED displays consist of a mono-color micro-LED array and color conversion materials to achieve full color, while relieving the burden of epitaxial growth of three-color micro-LEDs. However, it usually suffers from low efficiency and color crosstalk due to the limited optical density [...] Read more.

Color-converted micro-LED displays consist of a mono-color micro-LED array and color conversion materials to achieve full color, while relieving the burden of epitaxial growth of three-color micro-LEDs. However, it usually suffers from low efficiency and color crosstalk due to the limited optical density of color conversion materials. With funnel-tube array, the optical efficiency of the color-converted micro-LED display can be improved by ~3X, while the crosstalk is eliminated. After optimization of the tapper angle, the ambient contrast ratio is also improved due to higher light intensity. Full article

(This article belongs to the Special Issue Advanced LED Solid-State Lighting Optics)

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16 pages, 667 KiB

Open AccessEditor’s ChoiceReview

Peculiarities of Protein Crystal Nucleation and Growth

by Christo N. Nanev

Crystals 2018, 8(11), 422; https://doi.org/10.3390/cryst8110422 - 8 Nov 2018

Cited by 11 | Viewed by 4803

Abstract

This paper reviews investigations on protein crystallization. It aims to present a comprehensive rather than complete account of recent studies and efforts to elucidate the most intimate mechanisms of protein crystal nucleation. It is emphasized that both physical and biochemical factors are at [...] Read more.

This paper reviews investigations on protein crystallization. It aims to present a comprehensive rather than complete account of recent studies and efforts to elucidate the most intimate mechanisms of protein crystal nucleation. It is emphasized that both physical and biochemical factors are at play during this process. Recently-discovered molecular scale pathways for protein crystal nucleation are considered first. The bond selection during protein crystal lattice formation, which is a typical biochemically-conditioned peculiarity of the crystallization process, is revisited. Novel approaches allow us to quantitatively describe some protein crystallization cases. Additional light is shed on the protein crystal nucleation in pores and crevices by employing the so-called EBDE method (equilibration between crystal bond and destructive energies). Also, protein crystal nucleation in solution flow is considered. Full article

(This article belongs to the Special Issue Biological Crystallization)

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14 pages, 2116 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

NMR Crystallography of the Polymorphs of Metergoline

by Jiri Czernek, Martina Urbanova and Jiri Brus

Crystals 2018, 8(10), 378; https://doi.org/10.3390/cryst8100378 - 25 Sep 2018

Cited by 15 | Viewed by 4202

Abstract

Two polymorphs of the drug compound metergoline (C₂₅H₂₉N₃O₂) were investigated in detail by solid-state NMR measurements. The results have been analysed by an advanced procedure, which uses experimental input together with the results of quantum [...] Read more.

Two polymorphs of the drug compound metergoline (C₂₅H₂₉N₃O₂) were investigated in detail by solid-state NMR measurements. The results have been analysed by an advanced procedure, which uses experimental input together with the results of quantum chemical calculations that were performed for molecular crystals. In this way, it was possible to assign the total of 40 ¹H–¹³C correlation pairs in a highly complex system, namely, in the dynamically disordered polymorph with two independent molecules in the unit cell of a large volume of 4234 Å³. For the simpler polymorph, which exhibits only small-amplitude motions and has just one molecule in the unit cell with a volume of 529.0 Å³, the values of the principal elements of the ¹³C chemical shift tensors were measured. Additionally, for this polymorph, a set of crystal structure predictions were generated, and the {¹³C, ¹H} isotropic and ¹³C anisotropic chemical shielding data were computed while using the gauge-including projector augmented-wave approach combined with the “revised Perdew-Burke-Ernzerhof“ exchange-correlation functional (GIPAW-RPBE). The experimental and theoretical results were combined in an application of the newly developed strategy to polymorph discrimination. This research thus opens up new routes towards more accurate characterization of the polymorphism of drug formulations. Full article

(This article belongs to the Special Issue NMR Crystallography)

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26 pages, 4591 KiB

Open AccessEditor’s ChoiceReview

The Crystal Orbital Hamilton Population (COHP) Method as a Tool to Visualize and Analyze Chemical Bonding in Intermetallic Compounds

by Simon Steinberg and Richard Dronskowski

Crystals 2018, 8(5), 225; https://doi.org/10.3390/cryst8050225 - 18 May 2018

Cited by 210 | Viewed by 16376

Abstract

Recognizing the bonding situations in chemical compounds is of fundamental interest for materials design because this very knowledge allows us to understand the sheer existence of a material and the structural arrangement of its constituting atoms. Since its definition 25 years ago, the [...] Read more.

Recognizing the bonding situations in chemical compounds is of fundamental interest for materials design because this very knowledge allows us to understand the sheer existence of a material and the structural arrangement of its constituting atoms. Since its definition 25 years ago, the Crystal Orbital Hamilton Population (COHP) method has been established as an efficient and reliable tool to extract the chemical-bonding information based on electronic-structure calculations of various quantum-chemical types. In this review, we present a brief introduction into the theoretical background of the COHP method and illustrate the latter by diverse applications, in particular by looking at representatives of the class of (polar) intermetallic compounds, usually considered as “black sheep” in the light of valence-electron counting schemes. Full article

(This article belongs to the Special Issue Compounds with Polar Metallic Bonding)

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19 pages, 44833 KiB

Open AccessEditor’s ChoiceArticle

Tuning of Luminescent and Magnetic Properties via Metal Do** of Zn-BTC Systems

by Taoguang Qu, Qiang Wei, Carlos Ordonez, Jennifer Lindline, Michael Petronis, Marina S. Fonari and Tatiana Timofeeva

Crystals 2018, 8(4), 162; https://doi.org/10.3390/cryst8040162 - 8 Apr 2018

Cited by 7 | Viewed by 5927

Abstract

In order to assess how metal do** affects the luminescence and magnetic properties of anionic Metal-Organic Frameworks (MOFs), seven single-metal doped MOFs {M-Zn-BTC}{Me₂NH₂⁺} (M = Co, Cu, Ni, Mn, Ca, Mg, Cd) and three dual-metal doped MOFs {Zn-M [...] Read more.

In order to assess how metal do** affects the luminescence and magnetic properties of anionic Metal-Organic Frameworks (MOFs), seven single-metal doped MOFs {M-Zn-BTC}{Me₂NH₂⁺} (M = Co, Cu, Ni, Mn, Ca, Mg, Cd) and three dual-metal doped MOFs {Zn-M₁-M₂-BTC}{Me₂NH₂⁺} (M₁ = Co, Cu; M₂ = Ni, Co) were synthesized. Trace amounts of different metals were doped via addition of another metal salt during the synthetic process. All compounds retained the same crystal structure as that of the parent {Zn-BTC}{Me₂NH₂⁺} MOF, which was supported by single crystal and powder X-ray diffraction studies. Thermal Gravimetric Analysis (TGA) of these compounds also revealed that all MOFs had similar stability up to ~450 °C. Solid state photoluminescent studies indicated that {Zn-Mn-BTC}{Me₂NH₂⁺}, {Zn-Cd-BTC}{Me₂NH₂⁺}, and {Zn-Ca-BTC}{Me₂NH₂⁺} had a significant red shifting effect compared to the original {Zn-BTC}{Me₂NH₂⁺} MOF. Applications of this do** method to other MOF systems can provide an efficient way to tune the luminescence of such systems, and to obtain a desired wavelength for several applications such as sensors and white light LED materials. Because Zn, Co, Cu, Ni, Mg have magnetic properties, the effect of the do** metal atom on the magnetism of the {Zn-BTC}{Me₂NH₂⁺} networks was also studied. To characterize the magnetic behavior of the synthesized MOFs, we conducted low-temperature (10 K) saturation remanence experiments in a 3 Tesla applied field, with the principal goal of identifying the domain state of the synthesized materials (Zn, Zn-Co, Zn-Cu-Co, Zn-Cu-Ni, Zn-Mg, Zn-Mn, Zn-Ni-Co, Zn-Ni). During room/low temperature saturation magnetization experiments, Zn, Zn-Co, Zn-Cu-Co, and Zn-Cu-Ni systems yielded data indicative of superparamagnetic behavior, yet during zero field and field cooled experiments Zn-Co showed a slight paramagnetic effect, Zn showed no temperature dependence on warming and Zn-Cu-Co and Zn-Cu-Ni demonstrated only a slight temperature dependence on warming. These behaviors are consistent with ferromagnetic ordering. Zero field and field cooled experiments indicate that Zn-Mg and Zn-Ni have a ferromagnetic ordering and Zn-Mn and Zn-Ni-Co show paramagnetic ordering behavior. Full article

(This article belongs to the Special Issue Crystal Structure Analysis of Supramolecular and Porous Solids)

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13 pages, 14797 KiB

Open AccessEditor’s ChoiceReview

Radiation Damage in Macromolecular Crystallography—An Experimentalist’s View

by Helena Taberman

Crystals 2018, 8(4), 157; https://doi.org/10.3390/cryst8040157 - 4 Apr 2018

Cited by 13 | Viewed by 7852

Abstract

Radiation damage still remains a major limitation and challenge in macromolecular X-ray crystallography. Some of the high-intensity radiation used for diffraction data collection experiments is absorbed by the crystals, generating free radicals. These give rise to radiation damage even at cryotemperatures (~100 K), [...] Read more.

Radiation damage still remains a major limitation and challenge in macromolecular X-ray crystallography. Some of the high-intensity radiation used for diffraction data collection experiments is absorbed by the crystals, generating free radicals. These give rise to radiation damage even at cryotemperatures (~100 K), which can lead to incorrect biological conclusions being drawn from the resulting structure, or even prevent structure solution entirely. Investigation of mitigation strategies and the effects caused by radiation damage has been extensive over the past fifteen years. Here, recent understanding of the physical and chemical phenomena of radiation damage is described, along with the global effects inflicted on the collected data and the specific effects observed in the solved structure. Furthermore, this review aims to summarise the progress made in radiation damage studies in macromolecular crystallography from the experimentalist’s point of view and to give an introduction to the current literature. Full article

(This article belongs to the Special Issue Recent Advances in Protein Crystallography)

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15 pages, 3401 KiB

Open AccessEditor’s ChoiceArticle

Intra-/Intermolecular Bifurcated Chalcogen Bonding in Crystal Structure of Thiazole/Thiadiazole Derived Binuclear (Diaminocarbene)Pd^II Complexes

by Alexander S. Mikherdov, Alexander S. Novikov, Mikhail A. Kinzhalov, Andrey A. Zolotarev and Vadim P. Boyarskiy

Crystals 2018, 8(3), 112; https://doi.org/10.3390/cryst8030112 - 27 Feb 2018

Cited by 48 | Viewed by 5429

Abstract

The coupling of cis-[PdCl2(CNXyl)2] (Xyl = 2,6-Me2C6H3) with 4-phenylthiazol-2-amine in molar ratio 2:3 at RT in CH2Cl2 leads to binuclear (diaminocarbene)PdII complex 3c. The complex was characterized by HRESI+-MS, 1H NMR spectroscopy, and its structure was elucidated by single-crystal XRD. Inspection of [...] Read more.

The coupling of cis-[PdCl2(CNXyl)2] (Xyl = 2,6-Me2C6H3) with 4-phenylthiazol-2-amine in molar ratio 2:3 at RT in CH2Cl2 leads to binuclear (diaminocarbene)PdII complex 3c. The complex was characterized by HRESI+-MS, 1H NMR spectroscopy, and its structure was elucidated by single-crystal XRD. Inspection of the XRD data for 3c and for three relevant earlier obtained thiazole/thiadiazole derived binuclear diaminocarbene complexes (3a EYOVIZ; 3b: EYOWAS; 3d: EYOVOF) suggests that the structures of all these species exhibit intra-/intermolecular bifurcated chalcogen bonding (BCB). The obtained data indicate the presence of intramolecular S•••Cl chalcogen bonds in all of the structures, whereas varying of substituent in the 4th and 5th positions of the thiazaheterocyclic fragment leads to changes of the intermolecular chalcogen bonding type, viz. S•••π in 3a,b, S•••S in 3c, and S•••O in 3d. At the same time, the change of heterocyclic system (from 1,3-thiazole to 1,3,4-thiadiazole) does not affect the pattern of non-covalent interactions. Presence of such intermolecular chalcogen bonding leads to the formation of one-dimensional (1D) polymeric chains (for 3a,b), dimeric associates (for 3c), or the fixation of an acetone molecule in the hollow between two diaminocarbene complexes (for 3d) in the solid state. The Hirshfeld surface analysis for the studied X-ray structures estimated the contributions of intermolecular chalcogen bonds in crystal packing of 3a–d: S•••π (3a: 2.4%; 3b: 2.4%), S•••S (3c: less 1%), S•••O (3d: less 1%). The additionally performed DFT calculations, followed by the topological analysis of the electron density distribution within the framework of Bader’s theory (AIM method), confirm the presence of intra-/intermolecular BCB S•••Cl/S•••S in dimer of 3c taken as a model system (solid state geometry). The AIM analysis demonstrates the presence of appropriate bond critical points for these interactions and defines their strength from 0.9 to 2.8 kcal/mol indicating their attractive nature. Full article

(This article belongs to the Special Issue Chalcogen Bonding in Crystalline and Catalyst Materials)

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