Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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Article
Simplified Approach to Characterize the Cooling Crystallization in a Modular Mini-Plant
Crystals 2023, 13(1), 147; https://doi.org/10.3390/cryst13010147 - 14 Jan 2023
Viewed by 766
Abstract
The characterization of new process equipment often includes tedious experiments, particularly for (cooling) crystallization. This can be cost-intensive and time-consuming when the actual equipment has to be continuously operated to gain new insights. For multi-purpose plants that frequently change the process substance system, [...] Read more.
The characterization of new process equipment often includes tedious experiments, particularly for (cooling) crystallization. This can be cost-intensive and time-consuming when the actual equipment has to be continuously operated to gain new insights. For multi-purpose plants that frequently change the process substance system, this can be especially laborious. In order to accelerate the generation of characterization data for the quasi-continuous filter belt crystallizer (QCFBC), a Peltier-element-driven, simplified experimental benchtop setup is validated in this work using a sucrose/water model substance system. It was shown that the operation conditions during the cooling crystallization on the continuously operated plant can be appropriately emulated; therefore, an actual operation of the entire mini-plant for characterization experiments is no longer necessary. Full article
(This article belongs to the Section Industrial Crystallization)
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Article
L-Glu Hierarchical Structure Crystallization Using Inorganic Ions
Crystals 2023, 13(1), 121; https://doi.org/10.3390/cryst13010121 - 10 Jan 2023
Viewed by 730
Abstract
Hierarchical organic structures have gained vast attention in the past decade owing to their great potential in chemical and medical applications in industries such as the food and pharmaceutical industries. In this paper, the crystallization of L-glu hierarchical spheres using inorganic ions, namely [...] Read more.
Hierarchical organic structures have gained vast attention in the past decade owing to their great potential in chemical and medical applications in industries such as the food and pharmaceutical industries. In this paper, the crystallization of L-glu hierarchical spheres using inorganic ions, namely calcium, barium and strontium cations, is described. The anti-solvent precipitation method is used for the spherical crystallization. The L-glu microspheres are characterized using various techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photo-electron microscopy (XPS) and polarized microscopy (POM). It is shown that without additives, L-glu crystallizes as flower-like structures, very different from the hierarchical spheres crystallized with the charged additives. Based on our results, we suggest a mechanism for the hierarchical sphere formation based on the crystallization and self-assembly of L-glu in emulsion droplets using charged additives. Full article
(This article belongs to the Section Organic Crystalline Materials)
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Article
Crystal Engineering of Cation-Radical Salts with Weakly Coordinating Carbadodecaborate Anions
Crystals 2023, 13(1), 99; https://doi.org/10.3390/cryst13010099 - 05 Jan 2023
Cited by 1 | Viewed by 846
Abstract
An X-ray structural analysis revealed that the salts of N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD), N-methylphenothiazine (MPTZ), and octamethylbiphenylene (OMB), with dodecamethyl- or hexabromo-substituted carbadodecaborate anions, comprise layers of the (partially) oxidized organic donors separated by sheets of the bulky counter-ions. The cationic layers comprise either well-separated [...] Read more.
An X-ray structural analysis revealed that the salts of N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD), N-methylphenothiazine (MPTZ), and octamethylbiphenylene (OMB), with dodecamethyl- or hexabromo-substituted carbadodecaborate anions, comprise layers of the (partially) oxidized organic donors separated by sheets of the bulky counter-ions. The cationic layers comprise either well-separated TMPD+ or MPTZ+ cation radicals or π-stacks of partially oxidized OMB moieties consisting of more or less distinct (OMB)2+ units. Quantum mechanical calculations revealed that the formation of essentially isolated cation-radical or π-bonded associations in the salts with these weakly coordinating anions is correlated with the strength of the multicenter π-bonding between cation radicals. This pancake bonding is determined by the balance of the electrostatic repulsion between cationic counterparts and attractive dispersion and weakly covalent interactions. Full article
(This article belongs to the Special Issue Feature Papers in Crystal Engineering in 2022)
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Article
New Liquid Crystalline Elastomeric Films Containing a Smectic Crosslinker: Chemical and Physical Properties
Crystals 2023, 13(1), 96; https://doi.org/10.3390/cryst13010096 - 04 Jan 2023
Cited by 1 | Viewed by 824
Abstract
Side-chain liquid crystal elastomers (SC-LCEs) have been designed by using a new smectic crosslinker. Two types of monodomain films were prepared based on polysiloxane chains, with a different relative concentration of both crosslinker and mesogenic comonomers. The mesomorphic behavior of the two SC-LCE [...] Read more.
Side-chain liquid crystal elastomers (SC-LCEs) have been designed by using a new smectic crosslinker. Two types of monodomain films were prepared based on polysiloxane chains, with a different relative concentration of both crosslinker and mesogenic comonomers. The mesomorphic behavior of the two SC-LCE systems was investigated by differential scanning calorimetry and polarized optical microscopy showing a different mesomorphic behavior: in one case, we obtained a nematic SC-LCE film, in the other case, a Smectic A SC-LCE film. In both systems, the mesophases were stable in a wide temperature range. Moreover, the SC-LCE films possess a relatively high orientation at room temperature. The physical-chemical properties, such as the local orientational ordering, structural organization, and dynamics of SC-LCEs’ constituents were studied by means of static and dynamic 2H NMR experiments, small-angle X-ray, and wide-angle X-ray diffractions. The relevant physical properties, such as the thermo-elastic and thermo-mechanic behaviors, are reported and discussed in view of the practical applications. Full article
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Article
Interplay of Ionic Species in Salts of Homoleptic Quaternary Phosphonium Cations Bearing Linear Biphenyl Moieties
Crystals 2023, 13(1), 59; https://doi.org/10.3390/cryst13010059 - 29 Dec 2022
Viewed by 1154
Abstract
Quaternary phosphonium salts are popular candidates used in many chemical transformations and synthetic chemistry, notably in catalysis. We have examined the single crystals of two bulky phosphonium compounds, tetra([1,1′-biphenyl]-4-yl) phosphonium dicyanamide (C48H36P+·N(CN)2, compound 1 [...] Read more.
Quaternary phosphonium salts are popular candidates used in many chemical transformations and synthetic chemistry, notably in catalysis. We have examined the single crystals of two bulky phosphonium compounds, tetra([1,1′-biphenyl]-4-yl) phosphonium dicyanamide (C48H36P+·N(CN)2, compound 1), and tetra([1,1′-biphenyl]-4-yl) phosphonium bromide hydrate (C48H36P+·Br, CH3CN, H2O, compound 2), and herein report the structural properties for the compounds with an emphasis on the influence of the ion-ion interaction towards self-assembly; the overall self-assembly for both structures is very similar, with subtle differences in the cell parameters. The symmetrical tetra ([1,1′-biphenyl]-4-yl) phosphonium cations in both compounds self-assembled to form robust stacked columns in the solid-state, with voids occupied by anions or solvent molecules. Quantitative examination of intermolecular interactions using Hirshfeld surface analysis found that classical and non-classical hydrogen bonding appears to be the dominant contributor in stabilizing the self-assembly in both cases. The present work can not only benefit in understanding the mutual interaction between the sterically encumbered tetra ([1,1′-biphenyl]-4-yl) phosphonium cations and between counterions, but also provide insights for the self-assembled arrays in the solid-state. Full article
(This article belongs to the Special Issue Feature Papers in Crystal Engineering in 2022)
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Article
High-Pressure X-ray Diffraction and DFT Studies on Spinel FeV2O4
Crystals 2023, 13(1), 53; https://doi.org/10.3390/cryst13010053 - 28 Dec 2022
Viewed by 1170
Abstract
We have studied the behaviour of the cubic spinel structure of FeV2O4 under high-pressure by means of powder X-ray diffraction measurements and density-functional theory calculations. The sample was characterized at ambient conditions by energy-dispersive X-ray spectroscopy, Raman spectroscopy, and X-ray [...] Read more.
We have studied the behaviour of the cubic spinel structure of FeV2O4 under high-pressure by means of powder X-ray diffraction measurements and density-functional theory calculations. The sample was characterized at ambient conditions by energy-dispersive X-ray spectroscopy, Raman spectroscopy, and X-ray diffraction experiments. One of the main findings of this work is that spinel FeV2O4 exhibits pressure-induced chemical decomposition into V2O3 and FeO around 12 GPa. Upon pressure release, the pressure-induced chemical decomposition appears to be partially reversible. Additionally, in combination with density-functional theory calculations, we have calculated the pressure dependence of the unit-cell volumes of both the spinel and orthorhombic FeV2O4 crystal structures, whose bulk moduli are B0 = 123(9) and 154(2) GPa, respectively, finding the spinel FeV2O4 to exhibit the lowest bulk modulus amongst the spinel oxides. From experimental results, the same information is herein obtained for the cubic structure only. The Raman modes and elastic constants of spinel FeV2O4 have also obtained the ambient conditions. Full article
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Article
Effect of Sc Addition on High-Temperature Oxidation Performance of Al-Li Alloy
Crystals 2023, 13(1), 22; https://doi.org/10.3390/cryst13010022 - 23 Dec 2022
Viewed by 729
Abstract
Aluminum–lithium alloys were treated by high-temperature oxidation. The oxidation kinetics were analyzed by oxidation weighing. The surface morphology of the oxidized samples was observed by FESEM scanning electron microscopy. A phase analysis of the oxidized alloys was conducted by XRD. The outcomes demonstrate [...] Read more.
Aluminum–lithium alloys were treated by high-temperature oxidation. The oxidation kinetics were analyzed by oxidation weighing. The surface morphology of the oxidized samples was observed by FESEM scanning electron microscopy. A phase analysis of the oxidized alloys was conducted by XRD. The outcomes demonstrate that the aluminum–lithium alloy with a Sc element is oxidized at a high temperature under the same conditions, improving the high-temperature oxidation resistance, the weight increase from oxidation is minimal, and the oxidation kinetic reaction index is decreased. The resulting oxidation product is Li2CO3. The addition of a Sc element can prevent the movement of metal cations, improve the high-temperature oxidation resistance of Al–Li alloy to a certain extent, and the resulting oxide film is more complete and compact. Full article
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Article
A Tetranuclear Ni(II)-Cubane Cluster Molecule Build by Four µ3-O-Methanolate (MeO) Ligands, Externally Cohesive by Four Unprecedented Bridging µ2-N7,O6-Acyclovirate (acv-H) Anions
Crystals 2023, 13(1), 7; https://doi.org/10.3390/cryst13010007 - 21 Dec 2022
Viewed by 900
Abstract
Metal ion interactions with nuclei acids and their constituents represent a multi-faceted and growing research field. This contribution deals with molecular recognition between synthetic purine 17 nucleosides and first-row transition metal complexes, with O- and/or N-amino chelators which are able to 18 engage [...] Read more.
Metal ion interactions with nuclei acids and their constituents represent a multi-faceted and growing research field. This contribution deals with molecular recognition between synthetic purine 17 nucleosides and first-row transition metal complexes, with O- and/or N-amino chelators which are able to 18 engage in intra-molecular N-H···(N or O) and O-H···(N or O) interligand interactions. Crystals of these complexes can also display inter-molecular aromatic π-stacking and/or other non-conventional interactions. In this manuscript, we used 2-(2-aminoethoxy)ethanol (2aee) as a potential N,O(e),O(ol)-chelator for nickel(II). However, unexpectedly, the reaction between NiCl2, acyclovir (acv), and 2aee in methanol afforded parallelepiped apple-green crystals of [Ni(acv-H)(MeO)(H2O)]4·8H2O, (1) a tetranuclear molecule with an equimolar Ni(II):µ3-methanolate(1-):µ2-N7,O6-acyclovirate(1-) (acv-H) ratio. The µ2-N7,O6-(acv-H) metal-binding pattern (MBP) is unprecedented in terms of both its anionic and bridging roles. The single-crystal X-ray diffraction structure as well as thermogravimetric analysis and the (FT-IR +Vis-UV) spectra of 1 are reported. Theoretical density functional theory (DFT) calculations are used to analyse the antiparallel π-stacking interactions that govern the formation of self-assembled dimers in the solid state. Full article
(This article belongs to the Special Issue X-ray Crystallography and Drug Discovery)
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Article
Analysis of Thermal Effects in Kilowatt High Power Diamond Raman Lasers
Crystals 2022, 12(12), 1824; https://doi.org/10.3390/cryst12121824 - 14 Dec 2022
Cited by 1 | Viewed by 993
Abstract
Chemical vapor deposition (CVD) diamond crystal is considered as an ideal material platform for Raman lasers with both high power and good beam quality due to its excellent Raman and thermal characteristics. With the continuous development of CVD diamond crystal growth technology, diamond [...] Read more.
Chemical vapor deposition (CVD) diamond crystal is considered as an ideal material platform for Raman lasers with both high power and good beam quality due to its excellent Raman and thermal characteristics. With the continuous development of CVD diamond crystal growth technology, diamond Raman lasers (DRLs) have shown significant advantages in achieving wavelength expansion with both high beam quality and high-power operation. However, with the output power of DRLs reaching the kilowatt level, the adverse effect of the thermal impact on the beam quality is progressively worsening. Aiming to enunciate the underlying restrictions of the thermal effects for high-power DRLs (e.g., recently reported 1.2 kW), we here establish a thermal-structural coupling model, based on which the influence of the pump power, cavity structure, and crystal size have been systematically studied. The results show that a symmetrical concentric cavity has less thermal impact on the device than an asymmetrical concentric cavity. Under the ideal heat dissipation condition, the highest temperature rise in the diamond crystal is 23.4 K for an output power of ~2.8 kW. The transient simulation further shows that the heating and cooling process of DRLs is almost unaffected by the pump power, and the times to reach a steady state are only 1.5 ms and 2.5 ms, respectively. In addition, it is also found that increasing the curvature radius of the cavity mirror, the length and width of the crystal, or decreasing the thickness of the crystal is beneficial to alleviating the thermal impact of the device. The findings of this work provide some helpful insights into the design of the cavity structure and heat dissipation system of DRLs, which might facilitate their future development towards a higher power. Full article
(This article belongs to the Special Issue Frontiers of Semiconductor Lasers)
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Review
Recent Progress in Phase Stability and Elastic Anomalies of Group VB Transition Metals
Crystals 2022, 12(12), 1762; https://doi.org/10.3390/cryst12121762 - 05 Dec 2022
Cited by 1 | Viewed by 964
Abstract
Recently discovered phase transition and elastic anomaly of compression-induced softening and heating-induced hardening (CISHIH) in group VB transition metals at high-pressure and high-temperature (HPHT) conditions are unique and interesting among typical metals. This article reviews recent progress in the understanding of the structural [...] Read more.
Recently discovered phase transition and elastic anomaly of compression-induced softening and heating-induced hardening (CISHIH) in group VB transition metals at high-pressure and high-temperature (HPHT) conditions are unique and interesting among typical metals. This article reviews recent progress in the understanding of the structural and elastic properties of these important metals under HPHT conditions. Previous investigations unveiled the close connection of the remarkable structural stability and elastic anomalies to the Fermi surface nesting (FSN), Jahn–Teller effect, and electronic topological transition (ETT) in vanadium, niobium, and tantalum. We elaborate that two competing scenarios are emerging from these advancements. The first one focuses on phase transition and phase diagram, in which a soft-mode driven structural transformation of BCC→RH1→RH2→BCC under compression and an RH→BCC reverse transition under heating in vanadium were established by experiments and theories. Similar phase transitions in niobium and tantalum were also proposed. The concomitant elastic anomalies were considered to be due to the phase transition. However, we also showed that there exist some experimental and theoretical facts that are incompatible with this scenario. A second scenario is required to accomplish a physically consistent interpretation. In this alternative scenario, the electronic structure and associated elastic anomaly are fundamental, whereas phase transition is just an outcome of the mechanical instability. We note that this second scenario is promising to reconcile all known discrepancies but caution that the phase transition in group VB metals is elusive and is still an open question. A general consensus on the relationship between the possible phase transitions and the mechanical elasticity (especially the resultant CISHIH dual anomaly, which has a much wider impact), is still unreached. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Volume II))
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Article
Multicolor Photochromism of Two-Component Diarylethene Crystals Containing Oxidized and Unoxidized Benzothiophene Groups
Crystals 2022, 12(12), 1730; https://doi.org/10.3390/cryst12121730 - 29 Nov 2022
Cited by 1 | Viewed by 775
Abstract
Preparing mixed crystals composed of two or more components is one of the useful approaches to not only modifying the physical properties and chemical reactivity of molecular crystals but also creating their novel functionality. Here we report preparation and photoresponsive properties of two-component [...] Read more.
Preparing mixed crystals composed of two or more components is one of the useful approaches to not only modifying the physical properties and chemical reactivity of molecular crystals but also creating their novel functionality. Here we report preparation and photoresponsive properties of two-component mixed crystals containing photochromic bis(benzothienyl)ethene derivatives that show different colors in the closed-ring forms depending on the oxidation state of the benzothiophene groups. The similarity in the molecular structures of the two diarylethenes, which are different from each other only in the oxidation state of the benzothiophene groups, allowed the formation of two-component mixed crystals by recrystallization from mixed solutions containing the two compounds. Irradiating the mixed crystals with light of appropriate wavelengths induced the selective photoisomerizaion of the two diarylethenes, leading to multicolor photochromic performance, such as colorless, orange, yellow, and red. Such molecular crystals with multiresponsive functions can find potential applications in multistate optical recording and multicolor displays. The present results demonstrate that combining differently oxidized diarylethene derivatives is an effective strategy for preparing multicomponent mixed crystals with finely tuned composition and desired photoresponsive properties. Full article
(This article belongs to the Special Issue Photoresponsive Organic Molecular Crystals)
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Article
The Role of LPSO Structures in Corrosion Resistance of Mg-Y-Zn Alloys
Crystals 2022, 12(12), 1723; https://doi.org/10.3390/cryst12121723 - 27 Nov 2022
Viewed by 1096
Abstract
The growing interest in improving Mg-based alloys’ corrosion properties stimulates the development of Mg-Y-Zn alloys with long-period stacking-ordered (LPSO) structures. In this work, to describe the corrosion performance of Mg-LPSO alloys, a set of experiments, including microstructure observations and corrosion testing in media [...] Read more.
The growing interest in improving Mg-based alloys’ corrosion properties stimulates the development of Mg-Y-Zn alloys with long-period stacking-ordered (LPSO) structures. In this work, to describe the corrosion performance of Mg-LPSO alloys, a set of experiments, including microstructure observations and corrosion testing in media containing various concentrations of chloride ions, were carried out. It was shown that the main corrosion mechanism occurring on the alloys was not only related to the volume of LPSO structures in the Mg matrix but was also dependent on their distribution. In the chloride-containing solutions, pitting was the predominant corrosion mechanism, and with the increasing chloride concentration, microgalvanic corrosion was accelerated. Full article
(This article belongs to the Special Issue Light Metals and Their Alloys)
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Article
Numerical Simulation of Species Segregation and 2D Distribution in the Floating Zone Silicon Crystals
Crystals 2022, 12(12), 1718; https://doi.org/10.3390/cryst12121718 - 26 Nov 2022
Viewed by 1056
Abstract
The distribution of dopants and impurities in silicon grown with the floating zone method determines the electrical resistivity and other important properties of the crystals. A crucial process that defines the transport of these species is the segregation at the crystallization interface. To [...] Read more.
The distribution of dopants and impurities in silicon grown with the floating zone method determines the electrical resistivity and other important properties of the crystals. A crucial process that defines the transport of these species is the segregation at the crystallization interface. To investigate the influence of the melt flow on the effective segregation coefficient as well as on the global species transport and the resulting distribution in the grown crystal, we developed a new coupled numerical model. Our simulation results include the shape of phase boundaries, melt flow velocity and temperature, species distribution in the melt and, finally, the radial and axial distributions in the grown crystal. We concluded that the effective segregation coefficient is not constant during the growth process but rather increases for larger melt diameters due to less intensive melt mixing. Full article
(This article belongs to the Special Issue Crystallization Process and Simulation Calculation)
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Article
Multiscale Simulations for Defect-Controlled Processing of Group IV Materials
Crystals 2022, 12(12), 1701; https://doi.org/10.3390/cryst12121701 - 24 Nov 2022
Viewed by 1077
Abstract
Multiscale approaches for the simulation of materials processing are becoming essential to the industrialization of future nanotechnologies, as they allow for a reduction in production costs and an enhancement of devices and applications. Their integration as modules of “digital twins”, i.e., a combined [...] Read more.
Multiscale approaches for the simulation of materials processing are becoming essential to the industrialization of future nanotechnologies, as they allow for a reduction in production costs and an enhancement of devices and applications. Their integration as modules of “digital twins”, i.e., a combined sequence of predictive chemical–physical simulations and trained black-box techniques, should ideally complement the real sequence of processes throughout all development and production stages, starting from the growth of materials, their functional manipulation and finally their integration in nano-devices. To achieve this framework, computational implementations at different space and time scales are necessary, ranging from the atomistic to the macro-scale. In this paper, we propose a general paradigm for the industrially driven computational modeling of materials by deploying a multiscale methodology based on physical–chemical simulations bridging macro, meso and atomic scale. We demonstrate its general applicability by studying two completely different processing examples, i.e., the growth of group IV crystals through physical vapor deposition and their thermal treatment through pulsed laser annealing. We indicate the suitable formalisms, as well as the advantages and critical issues associated with each scale, and show how numerical methods for the solution of the models could be coupled to achieve a complete and effective virtualization of the process. By connecting the process parameters to atomic scale modifications such as lattice defects or faceting, we highlight how a digital twin module can gain intrinsic predictivity far from the pre-assessed training conditions of black-box “Virtual Metrology” techniques. Full article
(This article belongs to the Special Issue Feature Paper in "Materials for Energy Applications" 2022–2023)
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Article
Effect of Process Parameters on the Microstructure of Aluminum Alloys Made via Ultrasonic Additive Manufacturing
Crystals 2022, 12(12), 1696; https://doi.org/10.3390/cryst12121696 - 23 Nov 2022
Viewed by 960
Abstract
Ultrasonic additive manufacturing (UAM) has garnered significant interest in the aerospace and automotive industries for its structural lightweighting and multi-material joining capabilities. This paper details the investigation on the effect of process variables on the resultant microstructure of the built-up part using UAM [...] Read more.
Ultrasonic additive manufacturing (UAM) has garnered significant interest in the aerospace and automotive industries for its structural lightweighting and multi-material joining capabilities. This paper details the investigation on the effect of process variables on the resultant microstructure of the built-up part using UAM for aluminum 6061. The degree of recrystallization is quantified, and an energy metric, defined using the Read–Shockley relationship, is used to build an energy map of the welded part. The total energy stored in the resultant weld interface microstructure is quantified as a fraction of the input and is found to be about 0.1%. The width, average grain size, and percentage of High Angle Grain Boundaries (% HAGB) were used to compare microstructures of builds prepared using different processing conditions. Welding subsequent weld layers was not found to affect the previous welded layers. The effect of vibration amplitude and travel speed on the as-built microstructure were investigated, and the width of the interface was found to more than double when the weld amplitude is increased from the threshold value for joining (23 μm) and then stabilize at higher weld amplitudes. A better understanding of the effect of processing parameters on as-welded microstructures will assist parameter selection for UAM. Full article
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Article
Observation of Pattern Formation during Electromagnetic Levitation Using High-Speed Thermography
Crystals 2022, 12(12), 1691; https://doi.org/10.3390/cryst12121691 - 22 Nov 2022
Viewed by 897
Abstract
Electromagnetic levitation (EML) was employed for studying the velocity and morphology of the solidification front as a function of undercooling of metallic materials. The limitation of the EML technique with respect to low melting alloys that emit outside the visible light spectrum was [...] Read more.
Electromagnetic levitation (EML) was employed for studying the velocity and morphology of the solidification front as a function of undercooling of metallic materials. The limitation of the EML technique with respect to low melting alloys that emit outside the visible light spectrum was overcome by employing state-of-the-art high-speed mid-wavelength infrared cameras (MWIR cameras) with a photon detector. Due to the additional thermography contrast provided by the emission contrast of the solid and liquid phases, conductor, and semi-conductor, the pattern formation of Al-based alloys was studied in detail, revealing information on the nucleation, phase selection during solidification, and the influence of convection. Full article
(This article belongs to the Special Issue Phase Transition in External Fields)
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Article
A New Zero-Dimensional (CsK2)BiCl6 Metal Halide: Boosting Emission via B-Site Mn-Doping
Crystals 2022, 12(11), 1681; https://doi.org/10.3390/cryst12111681 - 21 Nov 2022
Cited by 1 | Viewed by 1110
Abstract
The A site of zero-dimensional (0D) metal halides A3BiCl6 can be replaced by Cs and/or K, thus, four possible 0D A3BiCl6 forms exist, such as (Cs2K)BiCl6, (CsK2)BiCl6, K3 [...] Read more.
The A site of zero-dimensional (0D) metal halides A3BiCl6 can be replaced by Cs and/or K, thus, four possible 0D A3BiCl6 forms exist, such as (Cs2K)BiCl6, (CsK2)BiCl6, K3BiCl6 and Cs3BiCl6. It is well known that Cs3BiCl6 has been reported. We predict that both (Cs2K)BiCl6 and K3BiCl6 do not have enough structural and thermodynamic stability, but (CsK2)BiCl6 should be a 0D stable A3BiCl6 candidate based on density functional theory (DFT). Furthermore, 0D (CsK2)BiCl6 metal halide was experimentally prepared by the solvothermal method. Though (CsK2)BiCl6 metal halide exhibits an indirect bandgap and poor luminescence properties, the emission can be boosted by B-site Mn-doping due to the efficient energy transfer from self-trapped excitons (STE) to the d-state of Mn ions. Our results enrich the family of 0D bi-based metal halides and provide guidance for the regulation of the structural and optical properties of metal halides. Full article
(This article belongs to the Special Issue Advances of Low-Dimensional Metal Halide Perovskite Materials)
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Review
Understanding Cysteine Chemistry Using Conventional and Serial X-ray Protein Crystallography
Crystals 2022, 12(11), 1671; https://doi.org/10.3390/cryst12111671 - 19 Nov 2022
Viewed by 1386
Abstract
Proteins that use cysteine residues for catalysis or regulation are widely distributed and intensively studied, with many biomedically important examples. Enzymes where cysteine is a catalytic nucleophile typically generate covalent catalytic intermediates whose structures are important for understanding mechanism and for designing targeted [...] Read more.
Proteins that use cysteine residues for catalysis or regulation are widely distributed and intensively studied, with many biomedically important examples. Enzymes where cysteine is a catalytic nucleophile typically generate covalent catalytic intermediates whose structures are important for understanding mechanism and for designing targeted inhibitors. The formation of catalytic intermediates can change enzyme conformational dynamics, sometimes activating protein motions that are important for catalytic turnover. However, these transiently populated intermediate species have been challenging to structurally characterize using traditional crystallographic approaches. This review describes the use and promise of new time-resolved serial crystallographic methods to study cysteine-dependent enzymes, with a focus on the main (Mpro) and papain-like (PLpro) cysteine proteases of SARS-CoV-2, as well as on other examples. We review features of cysteine chemistry that are relevant for the design and execution of time-resolved serial crystallography experiments. In addition, we discuss emerging X-ray techniques, such as time-resolved sulfur X-ray spectroscopy, that may be able to detect changes in sulfur charge states and covalency during catalysis or regulatory modification. In summary, cysteine-dependent enzymes have features that make them especially attractive targets for new time-resolved serial crystallography approaches, which can reveal both changes to enzyme structures and dynamics during catalysis in crystalline samples. Full article
(This article belongs to the Special Issue Novel Structural Studies of Coronavirus Proteins)
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Article
End-of-Life Liquid Crystal Displays Recycling: Physico-Chemical Properties of Recovered Liquid Crystals
Crystals 2022, 12(11), 1672; https://doi.org/10.3390/cryst12111672 - 19 Nov 2022
Viewed by 1298
Abstract
This report focuses particularly on liquid crystals display (LCD) panels because they represent a significant amount of all WEEE collected. Technologies involving liquid crystals (LCs) have enjoyed considerable success since the 1970s in all fields of LC displays (LCDs). This currently provokes the [...] Read more.
This report focuses particularly on liquid crystals display (LCD) panels because they represent a significant amount of all WEEE collected. Technologies involving liquid crystals (LCs) have enjoyed considerable success since the 1970s in all fields of LC displays (LCDs). This currently provokes the problem of waste generated by such equipment. Based on current statistical data, the LC amount represents approximately 1.3 g for a 35-inch diameter LCD panel unit possessing a total weight of 15 kg. In France, a recent study revealed LCD waste to represent an average of 5.6 panels per household. This represents an important quantity of LCs, which are generally destroyed by incineration or washed out with detergents during the recycling processes of end-of-life (EOL) LCDs. Hence, the aim of this study is to show that it is possible to remove LC molecules from EOL-LCD panels with the goal of valorizing them in new sectors. EOL-LCD panels have undergone various stages of dismantling, chemical treatments and characterization. The first stage of manual dismantling enables the elimination of the remaining physical components of the panels to process LC molecules only, sandwiched between the two glass plates. Mechanical treatment by scraping allows us to obtain a concentrate of LCs. The results obtained from chemical and physical techniques show that these molecules retain the characteristics essential for their operation in the field of optical and electro-optical devices. As the use of LCD surfaces continues to rise significantly, the amounts and economic stakes are huge, fully justifying the development of an LC recovery process for used panels. Many potential uses have been identified for these LC molecules: in new flat LCD panels after purification of the LCs concentrate, in PDLC systems, as lubricants or in thermal applications. Full article
(This article belongs to the Special Issue Advances in Liquid Crystal Optical Device)
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Article
Transient THz Emission and Effective Mass Determination in Highly Resistive GaAs Crystals Excited by Femtosecond Optical Pulses
Crystals 2022, 12(11), 1635; https://doi.org/10.3390/cryst12111635 - 14 Nov 2022
Viewed by 993
Abstract
We present comprehensive studies on the emission of broadband, free-space THz transients from several highly resistive GaAs samples excited by femtosecond optical pulses. Our test samples are characterized by different degrees of disorder, ranging from nitrogen-implanted to semi-insulating and annealed semi-insulating GaAs crystals. [...] Read more.
We present comprehensive studies on the emission of broadband, free-space THz transients from several highly resistive GaAs samples excited by femtosecond optical pulses. Our test samples are characterized by different degrees of disorder, ranging from nitrogen-implanted to semi-insulating and annealed semi-insulating GaAs crystals. In our samples, we clearly observed transient THz emissions due to the optical rectification effect, as well as due to the presence of the surface depletion electrical field. Next, we arranged our experimental setup in such way that we could observe directly how the amplitude of surface-emitted THz optical pulses is affected by an applied, in-plane magnetic field. We ascribe this effect to the Lorentz force that additionally accelerates optically excited carriers. The magnetic-field factor η is a linear function of the applied magnetic field and is the largest for an annealed GaAs sample, while it is the lowest for an N-implanted GaAs annealed at the lowest (300 °C) temperature. The latter is directly related to the longest and shortest trapping times, respectively, measured using a femtosecond optical pump-probe spectroscopy technique. The linear dependence of the factor η on the trapping time enabled us to establish that, for all samples, regardless of their crystalline structure, the electron effective mass was equal to 0.059 of the electron mass m0, i.e., it was only about 6% smaller than the generally accepted 0.063m0 value for GaAs with a perfect crystalline structure. Full article
(This article belongs to the Special Issue Terahertz Wave Generation in Nonlinear Optical Crystals)
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Article
Determination of Crystal Growth Rates in Multi-Component Solutions
Crystals 2022, 12(11), 1568; https://doi.org/10.3390/cryst12111568 - 03 Nov 2022
Cited by 1 | Viewed by 1363
Abstract
Many solid forming processes involve crystallization from multi-component solutions. In order to predict final phase assemblages, multi-component phase transfer kinetics must be known. It is not sufficient to have the kinetics of only one crystallizing component in the presence of other entities; the [...] Read more.
Many solid forming processes involve crystallization from multi-component solutions. In order to predict final phase assemblages, multi-component phase transfer kinetics must be known. It is not sufficient to have the kinetics of only one crystallizing component in the presence of other entities; the kinetics of concurrent crystallizing components are of interest as well. However, methods for their determination are currently lacking. We propose a new method comprising desupersaturation measurements of a 150 µm film of supersaturated solution in contact with a planar crystalline substrate. We show that concentration measurement at a single point in the film is sufficient to retrieve the phase transfer kinetics. For this, we use a confocal micro-Raman spectroscope, which is able to distinguish between different components and has a high spatial resolution. We chose crystallization of Na2SO4 and Na2CO3 decahydrate from aqueous solution as our model system because of its well-known phase equilibrium. In binary experiments, we demonstrate the mode of operation and its ability to reproduce known kinetics from the literature. In ternary experiments, we successfully distinguish two courses of crystallization, the first of which is a preferential crystallization of one component and the second a simultaneous crystallization of both crystallizing components. In both cases, the parameters for simple power law kinetics are determined. If sodium carbonate decahydrate crystallizes while sodium sulfate remains in solution, the mean mass transfer coefficient is revealed to be kg,CO3=6×107ms1, which is about an order of magnitude lower compared to binary crystallization. If sodium carbonate decahydrate crystallizes concurrently with sodium sulfate decahydrate, the crystallization kinetics are similar to binary cases. The other component tends to be significantly slower compared to its binary crystallization. Full article
(This article belongs to the Special Issue Aggregation, Nucleation and Crystallization)
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Article
Anisotropic Surface Formation Based on Brush-Coated Nickel-Doped Yttrium Oxide Film for Enhanced Electro-Optical Characteristics in Liquid Crystal Systems
Crystals 2022, 12(11), 1554; https://doi.org/10.3390/cryst12111554 - 31 Oct 2022
Viewed by 891
Abstract
This paper introduces anisotropic nickel yttrium oxide (NYO) film formed by the brush coating technique. X-ray photoelectron spectroscopy confirmed well-formed NYO film after the curing process, and the morphology of the surface was investigated using atomic force microscopy. The shear stress driven from [...] Read more.
This paper introduces anisotropic nickel yttrium oxide (NYO) film formed by the brush coating technique. X-ray photoelectron spectroscopy confirmed well-formed NYO film after the curing process, and the morphology of the surface was investigated using atomic force microscopy. The shear stress driven from brush hair movements caused the nano/micro-grooved anisotropic surface structure of NYO. This anisotropic surface induced uniform liquid crystal (LC) alignment on the surface, which was confirmed by pre-tilt angle analysis and polarized optical microscopy. The contact angle measurements revealed an increase in hydrophilicity at higher temperature curing, which contributed to homogenous LC alignment. The NYO film achieved good optical transmittance and thermal stability as an LC alignment layer. In addition, the film demonstrated good electro-optical properties, stable switching, and significantly enhanced operating voltage performance in a twisted-nematic LC system. Therefore, we expect that this brush coating method can be applied to various inorganic materials to achieve an advanced LC alignment layer. Full article
(This article belongs to the Special Issue Advances in Liquid Crystal Optical Device)
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Article
Comparative Study of the Compressibility of M3V2O8 (M = Cd, Zn, Mg, Ni) Orthovanadates
Crystals 2022, 12(11), 1544; https://doi.org/10.3390/cryst12111544 - 28 Oct 2022
Cited by 5 | Viewed by 1137
Abstract
We report herein a theoretical study of the high-pressure compressibility of Cd3V2O8, Zn3V2O8, Mg3V2O8, and Ni3V2O8. For Cd3 [...] Read more.
We report herein a theoretical study of the high-pressure compressibility of Cd3V2O8, Zn3V2O8, Mg3V2O8, and Ni3V2O8. For Cd3V2O8, we also present a study of its structural stability. Computer simulations were performed by means of first-principles methods using the CRYSTAL program. In Cd3V2O8, we found a previously unreported polymorph which is thermodynamically more stable than the already known polymorph. We also determined the compressibility of all compounds and evaluated the different contributions of polyhedral units to compressibility. We found that the studied vanadates have an anisotropic response to compression and that the change in volume is basically determined by the compressibility of the divalent-cation coordination polyhedra. A systematic discussion of the bulk modulus of M3V2O8 orthovanadates will also be included. Full article
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Article
Improved Electrical Performance of InAlN/GaN High Electron Mobility Transistors with Post Bis(trifluoromethane) Sulfonamide Treatment
Crystals 2022, 12(11), 1521; https://doi.org/10.3390/cryst12111521 - 26 Oct 2022
Viewed by 1019
Abstract
An enhancement of the electrical performance of the InAlN/GaN high electron mobility transistors (HEMTs) is demonstrated by the incorporation of post bis(trifluoromethane) sulfonamide (TFSI) treatment. The surface treatment of TFSI solution results in the increase of 2DEG electron mobility from 1180 to 1500 [...] Read more.
An enhancement of the electrical performance of the InAlN/GaN high electron mobility transistors (HEMTs) is demonstrated by the incorporation of post bis(trifluoromethane) sulfonamide (TFSI) treatment. The surface treatment of TFSI solution results in the increase of 2DEG electron mobility from 1180 to 1500 cm2/Vs and thus a reduction of on-state resistance and an increase in transconductance. The results indicate that the positive charge of H+ will decrease the polarization charges of the InAlN barrier under the access region due to the converse piezoelectric effect, leading to the reduced polarization Coulomb field (PCF) scattering in InAlN/GaN HEMT. This offers a possible way to improve the electron mobility and device performance of InAlN/GaN HEMTs for further application. Full article
(This article belongs to the Special Issue Wide-Bandgap Semiconductors)
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Article
In Situ Synchrotron Radiation Diffraction Study of Compression of AZ91 Composites Reinforced with Recycled Carbon Fibres
Crystals 2022, 12(11), 1502; https://doi.org/10.3390/cryst12111502 - 22 Oct 2022
Viewed by 1188
Abstract
Lightweight structural materials are increasingly sought after in the automotive and aerospace industries for their potential to improve fuel efficiency. Magnesium-based metal-matrix composites are potential candidates for these kinds of applications. The use of recycled carbon fibres offers further energy and cost savings. [...] Read more.
Lightweight structural materials are increasingly sought after in the automotive and aerospace industries for their potential to improve fuel efficiency. Magnesium-based metal-matrix composites are potential candidates for these kinds of applications. The use of recycled carbon fibres offers further energy and cost savings. The recycled carbon fibre composites were manufactured by stir casting with high-dispersion shearing, then were extruded and subsequently heat treated. The compressive deformation mechanisms of the composites compared to AZ91 were investigated using in situ synchrotron radiation diffraction. An increase in ultimate compressive strength was achieved in the composites compared to AZ91. The deformation mechanisms active in the composites were similar to those in AZ91. Magnesium alloys in compression typically show extensive twinning; this was observed in AZ91 and the AZ91 composites. The stress required for twinning onset was increased in the composites, and the twin volume fraction at failure was decreased compared to AZ91. Full article
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Article
Synthesis, Crystal and Electronic Structures, Nonlinear Optical Properties, and Magnetic Properties of Two Thiophosphates: KInP2S7 and KCrP2S7
Crystals 2022, 12(11), 1505; https://doi.org/10.3390/cryst12111505 - 22 Oct 2022
Viewed by 1089
Abstract
Two thiophosphates, KInP2S7 and KCrP2S7, were structurally characterized without investigating any optical properties. Herein in this work, KInP2S7 and KCrP2S7 were revisited to investigate their optical and magnetic properties, respectively. [...] Read more.
Two thiophosphates, KInP2S7 and KCrP2S7, were structurally characterized without investigating any optical properties. Herein in this work, KInP2S7 and KCrP2S7 were revisited to investigate their optical and magnetic properties, respectively. Pure polycrystalline samples and crystals of KInP2S7 and KCrP2S7 were grown by high temperature solid state reactions, where mm-sized crystals of KCrP2S7 were collected. KCrP2S7 is isostructural to KInP2S7, which features a layered structure. KInP2S7 and KCrP2S7 possess close relationship to the layered thiophosphate M2P2S6 (M = Fe, Co, Zn, etc.). The bonding pictures of KInP2S7 were studied using the electron localization function (ELF) coupled with crystal orbital Hamilton population (COHP) calculations. The intrinsically distorted [PS4] tetrahedra and [InS6] octahedra are made by strong covalent P-S interactions and ionic In-S interactions, respectively. Electronic structure analysis confirmed that the optical properties of KInP2S7 are mainly contributed to by [PS4] tetrahedra together with small amounts of the contributions coming from [InS6] octahedra. Magnetic measurement on mm-sized crystals of KCrP2S7 verified that there is an antiferromagnetic transition around 21 K, and the Cr atoms are trivalent. KInP2S7 is predicated to be an indirect bandgap semiconductor of 2.38 eV, which is confirmed by the UV-Vis measurement of 2.4(1) eV. KInP2S7 is not a type-I phase-matching material and exhibits moderate second harmonic generation (SHG) response (0.51 × AgGaS2, sample of particle size of 100 µm). The laser damage threshold (LDT) of KInP2S7 is very high of 5.2 × AgGaS2. Bandgap engineering were undergone to enhance the SHG response of KInP2S7. Full article
(This article belongs to the Special Issue Recent Advances in Nonlinear Optical Crystals)
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Article
Nickel-Assisted Transfer-Free Technology of Graphene Chemical Vapor Deposition on GaN for Improving the Electrical Performance of Light-Emitting Diodes
Crystals 2022, 12(10), 1497; https://doi.org/10.3390/cryst12101497 - 21 Oct 2022
Cited by 2 | Viewed by 845
Abstract
With the rapid development of graphene technology, today graphene performs well in the application of light-emitting diode (LED) transparent electrodes. Naturally, high-quality contact between the graphene and the GaN underneath is very important. This paper reports a process for nickel-assisted transfer-free technology of [...] Read more.
With the rapid development of graphene technology, today graphene performs well in the application of light-emitting diode (LED) transparent electrodes. Naturally, high-quality contact between the graphene and the GaN underneath is very important. This paper reports a process for nickel-assisted transfer-free technology of graphene chemical vapor deposition on GaN. The nickel film plays the dual role of etching mask and growth catalyst, and is removed by the subsequent “penetration etching” process, achieving good direct contact between the graphene and GaN. The results show that the graphene effectively improves the current spreading of GaN-based LEDs and enhances their electrical performance. This scheme avoids the wrinkles and cracks of graphene from the transfer process, and is not only suitable for the combination of graphene and GaN-based LEDs, but also provides a solution for the integration of graphene and other materials. Full article
(This article belongs to the Special Issue Recent Advances in III-Nitride Semiconductors)
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Article
2D Monte Carlo Simulation of Cocrystal Formation Using Patchy Particles
Crystals 2022, 12(10), 1457; https://doi.org/10.3390/cryst12101457 - 15 Oct 2022
Viewed by 778
Abstract
Cocrystals of Active Pharmaceutical Ingredients (APIs) are an attractive therapeutic alternative to salt formations. However, due to the molecular scale processes involved, the earliest stages of cocrystal formation remain poorly understood. In this paper, some light is shed on the thermodynamics and kinetics [...] Read more.
Cocrystals of Active Pharmaceutical Ingredients (APIs) are an attractive therapeutic alternative to salt formations. However, due to the molecular scale processes involved, the earliest stages of cocrystal formation remain poorly understood. In this paper, some light is shed on the thermodynamics and kinetics of co-crystallization. Importantly, to mimic the molecular scale processes of cocrystal formation, we use 2D Monte Carlo simulations and a computational model with short-range attraction and a mixture of two types of patchy particles (PPs) monomers. Each type possesses four patches, grouped in two by two, and each couple of patches is characterized by its specific placement on the circumference of the monomer and corresponding patch strength (a strong and narrow or weak and wide interaction). The spatial placement of the patches on both PPs monomers (alternating periodically through 60 and 120 degrees and vice versa) selected by us shows the emergence of both rhombohedral (metastable) and trihexagonal (stable) Kagome-like structures. The Kagome-like structures are preceded by formation of two types of trimers involving strong bonds only, or mixed trimers of strong and weak bonds, the later serving as building blocks for the finally generated Kagome patchy cocrystal, after prolonged simulation times. The step-by step process governing the cocrystal formation is discussed in detail, concerning the temperature interval, concentrations of PPs, the specific patch geometry and patch anisotropy as well. It is to be hoped that an understanding of the mechanisms of co-crystallization can help to control practical cocrystal synthesis and the possible phase transformations. Full article
(This article belongs to the Special Issue Aggregation, Nucleation and Crystallization)
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Article
Melt-Pool Dynamics and Microstructure of Mg Alloy WE43 under Laser Powder Bed Fusion Additive Manufacturing Conditions
Crystals 2022, 12(10), 1437; https://doi.org/10.3390/cryst12101437 - 12 Oct 2022
Viewed by 1273
Abstract
Magnesium-based alloy WE43 is a state-of-the-art bioresorbable metallic implant material. There is a need for implants with both complex geometries to match the mechanical properties of bone and refined microstructure for controlled resorption. Additive manufacturing (AM) using laser powder bed fusion (LPBF) presents [...] Read more.
Magnesium-based alloy WE43 is a state-of-the-art bioresorbable metallic implant material. There is a need for implants with both complex geometries to match the mechanical properties of bone and refined microstructure for controlled resorption. Additive manufacturing (AM) using laser powder bed fusion (LPBF) presents a viable fabrication method for implant applications, as it offers near-net-shape geometrical control, allows for geometry customization based on an individual patient, and fast cooling rates to achieve a refined microstructure. In this study, the laser–alloy interaction is investigated over a range of LPBF-relevant processing conditions to reveal melt-pool dynamics, pore formation, and the microstructure of laser-melted WE43. In situ X-ray imaging reveals distinct laser-induced vapor depression morphology regimes, with minimal pore formation at laser-scan speeds greater than 500 mm/s. Optical and electron microscopy of cross-sectioned laser tracks reveal three distinct microstructural regimes that can be controlled by adjusting laser-scan parameters: columnar, dendritic, and banded microstructures. These regimes are consistent with those predicted by the analytic solidification theory for conduction-mode welding, but not for keyhole-mode tracks. The results provide insight into the fundamental laser–material interactions of the WE43 alloy under AM-processing conditions and are critical for the successful implementation of LPBF-produced WE43 parts in biomedical applications. Full article
(This article belongs to the Special Issue Advances in Magnesium Alloys: Microstructure, Coating, and Machining)
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Article
Biological Mineralization of Hydrophilic Intraocular Lenses
Crystals 2022, 12(10), 1418; https://doi.org/10.3390/cryst12101418 - 08 Oct 2022
Viewed by 939
Abstract
Biomaterials calcify upon implantation in contact with biological fluids, which are supersaturated with respect to more than one crystalline phase of calcium phosphate. The implantation of intraocular lenses (IOLs) for cataract treatment has been hailed as a major advance. Hydrophilic acrylic IOLs, made [...] Read more.
Biomaterials calcify upon implantation in contact with biological fluids, which are supersaturated with respect to more than one crystalline phase of calcium phosphate. The implantation of intraocular lenses (IOLs) for cataract treatment has been hailed as a major advance. Hydrophilic acrylic IOLs, made of Poly(2-hydroxyethyl methacrylate) (PHEMA), upon contact with aqueous humor, exhibit significant incidence of opacification, due to the formation of calcium phosphate crystals, mainly hydroxyapatite (Ca5(PO4)3OH, HAP) on the surface or in their interior. The aqueous humor is supersaturated with respect to HAP. Clinical findings were duplicated by laboratory experiments through the development of appropriate experimental models which included batch reactors, well stirred operating at constant supersaturation (CCR) and reactors simulating anterior eye chamber (ECSR). In both CCR and ECSR, simulated aqueous humor was used. In ECSR the flow rate was the same as in the eye chamber (2.5 mL per 24 h). HAP formed both on the surface and inside the IOLs tested. Induction times preceding the crystallization of HAP on the surface of the IOLs and crystal growth rates were measured. Surface hydroxyl ionized groups favored the development of locally high supersaturation by surface complexation. In the interior of the IOLs, HAP formed by the diffusion of the calcium and phosphate ions inside the polymeric matrix. Full article
(This article belongs to the Special Issue Feature Papers in Biomolecular Crystals in 2022-2023)
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Article
Preparation of Large Volume Solid Argon Crystal and Its Feasibility Test as a Scintillation Material
Crystals 2022, 12(10), 1416; https://doi.org/10.3390/cryst12101416 - 07 Oct 2022
Viewed by 1006
Abstract
An important background to the liquid argon detectors is that they are caused by the diffusion of radioactive isotopes in a scintillator (liquid phase). This radioactive isotope is produced in argon’s surrounding devices, such as circulation pipelines and liquid argon containers. The solid [...] Read more.
An important background to the liquid argon detectors is that they are caused by the diffusion of radioactive isotopes in a scintillator (liquid phase). This radioactive isotope is produced in argon’s surrounding devices, such as circulation pipelines and liquid argon containers. The solid argon as a scintillation material in the detector can inhibit the diffusion and drift of radioactive isotopes in a solid phase scintillator. Additionally, the structure of a solid argon detector is simple and reduces the total source of radioactive background. In the CDEX-300 detection system, solid argon could substitute for liquid argon as the veto detector, preventing radioactive isotopes drifting to the central main detector (HPGe detectors array) surface to reduce backgrounds. Therefore, solid argon has great potential in the experiments since it is especially helpful to get the lower background in a larger active volume than liquid argon required in those low background detection experiments. This work introduces the preparation process and device of the large volume transparent crystalline argon, the acquisition of scintillation light, and the pulse amplitude spectrum of 137Cs obtained from a prototype detector of transparent solid argon crystal. The results show that the scheme proposed in this study can successfully produce a large volume transparent crystalline argon detector, the scintillation light signals can be effectively obtained from the solid argon scintillator, and the corresponding pulse amplitude spectrum is given. This work indicates that it is feasible to develop a solid argon crystal scintillation detector by using our approach. Full article
(This article belongs to the Special Issue Optoelectronics and Photonics in Crystals)
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Article
A Lection in Humbleness: Crystallization of Chiral and Zwitterionic APIs Baclofen and Phenibut
Crystals 2022, 12(10), 1393; https://doi.org/10.3390/cryst12101393 - 01 Oct 2022
Cited by 2 | Viewed by 1119
Abstract
Crystallization and multicomponent crystal formation of active pharmaceutical ingredients Baclofen and Phenibut with dicarboxylic acid co-formers are discussed. The crystallization process of several crystalline entities is elucidated via single crystal—as well as powder X-ray—diffraction, followed by thermal analysis and phase stability studies over [...] Read more.
Crystallization and multicomponent crystal formation of active pharmaceutical ingredients Baclofen and Phenibut with dicarboxylic acid co-formers are discussed. The crystallization process of several crystalline entities is elucidated via single crystal—as well as powder X-ray—diffraction, followed by thermal analysis and phase stability studies over time. Both APIs form increasingly complex crystalline phases with co-formers malic and tartaric acid, where phase purity of a desired compound is not necessarily a given. Therefore, the influence of different solution and milling environments during crystallization on the outcome is studied. Emphasis is laid on how molecular influences such as the chirality, propensity to form hydrates as well as low solubility of Baclofen and Phenibut impede attempts to gather high-quality single crystals. The results highlight that targeted crystallization of these compounds with dicarboxylic acids can be difficult and unreliable. Full article
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Article
The Family of MII3(TeIVO3)2(OH)2 (M = Mg, Mn, Co, Ni) Compounds—Prone to Inclusion of Foreign Components into Large Hexagonal Channels
Crystals 2022, 12(10), 1380; https://doi.org/10.3390/cryst12101380 - 28 Sep 2022
Cited by 3 | Viewed by 1088
Abstract
MII3(TeIVO3)2(OH)2 (M = Mg, Mn, Co, Ni) compounds crystallize isotypically in the hexagonal space group P63mc (No. 186) with unit-cell parameters of a ≈ 13 Å, c ≈ 5 [...] Read more.
MII3(TeIVO3)2(OH)2 (M = Mg, Mn, Co, Ni) compounds crystallize isotypically in the hexagonal space group P63mc (No. 186) with unit-cell parameters of a ≈ 13 Å, c ≈ 5 Å. In the crystal structure, a framework with composition M3(TeO3)2(OH)1.50.5+ defines large hexagonal channels extending along [001] where the remaining OH anions are located. Crystal-growth studies under mild hydrothermal conditions with subsequent structure analyses on basis of X-ray diffraction methods revealed that parts of other anions present in solution such as CO32−, SO42−, SeO42−, NO3, Cl or Br could partly replace the OH anions in the channels. The incorporation of such anions into the M3(TeO3)2(OH)2 structure was confirmed by energy-dispersive X-ray spectrometry (EDS) measurements and Raman spectroscopy of selected single-crystals. Full article
(This article belongs to the Section Inorganic Crystalline Materials)
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Article
Composition Engineering of (Lu,Gd,Tb)3(Al,Ga)5O12:Ce Film/Gd3(Al,Ga)5O12:Ce Substrate Scintillators
Crystals 2022, 12(10), 1366; https://doi.org/10.3390/cryst12101366 - 27 Sep 2022
Cited by 5 | Viewed by 1056
Abstract
The paper addresses the development of composite scintillation materials providing simultaneous real-time monitoring of different types of ionizing radiation (α-, β-particles, γ-rays) in mixed fluxes of particles and quanta. The detectors are based on composite heavy oxide scintillators consisting of a thin single-crystalline [...] Read more.
The paper addresses the development of composite scintillation materials providing simultaneous real-time monitoring of different types of ionizing radiation (α-, β-particles, γ-rays) in mixed fluxes of particles and quanta. The detectors are based on composite heavy oxide scintillators consisting of a thin single-crystalline film and a bulk single-crystal substrate. The film and substrate respond to certain types of ionizing particles, forming together an all-in-one composite scintillator capable of distinguishing the type of radiation through the different time characteristics of the scintillation response. Here, we report the structure, composition, and scintillation properties under different ionizing radiations of (Lu,Gd,Tb)3(Al,Ga)5O12:Ce films deposited using liquid phase epitaxy onto Gd3(Al1−xGax)5O12:Ce (GAGG:Ce) single-crystal substrates. The most promising compositions with the highest light yields and the largest differences in scintillation decay timing under irradiation with α-, β-particles, and γ-rays were selected. Such detectors are promising for environmental security purposes, medical tomography, and other radiation detection applications. Full article
(This article belongs to the Special Issue Crystals, Films and Nanocomposite Scintillators (Volume II))
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Article
Control of 11-Aza:4-X-SalA Cocrystal Polymorphs Using Heteroseeds That Switch On/Off Halogen Bonding
Crystals 2022, 12(10), 1368; https://doi.org/10.3390/cryst12101368 - 27 Sep 2022
Viewed by 859
Abstract
A family of: 1:1 cocrystals 11-Aza:4-X-SalA have been prepared from the potent anti-malarial compound 11-azaartemisinin with 4-halosalicylic acids. When X = 4-Cl, 4-Br and 4-I, two conformational polymorphs can be isolated in each case. Monoclinic type-I was found previously for parent 11-Aza:SalA ( [...] Read more.
A family of: 1:1 cocrystals 11-Aza:4-X-SalA have been prepared from the potent anti-malarial compound 11-azaartemisinin with 4-halosalicylic acids. When X = 4-Cl, 4-Br and 4-I, two conformational polymorphs can be isolated in each case. Monoclinic type-I was found previously for parent 11-Aza:SalA (1) and 11-Aza:4-Br-SalA (3a) which have polar 21 stacks of molecular pairs with no short halogen bond contacts between stacks. Orthorhombic type-II is found for 4-Cl (3b) and 4-I (4b) from solution growth. This has a translational stack of molecular pairs involving a conformational change of the acid-lactam hetero-synthon and supramolecular association of stacks via halogen bonds. Notably, phase pure polymorph type-I can be formed for 4-Cl (3a) and 4-I (4a) by hetero-seeding with 11-Aza:SalA, whist conversely phase pure type-II for 4-Br (2b) can be formed using homo-seeding from liquid assisted grinding (LAG) product. This work demonstrates both the viability of engineering polymorphic cocrystal forms using hetero-seeds and the involvement of halogen bonds in helping to discriminate quite different polymorphic types. Full article
(This article belongs to the Special Issue Advances in Functional Cocrystals)
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Article
The Microstructures and Mechanical Properties of a Welded Ni-Based Hastelloy X Superalloy
Crystals 2022, 12(10), 1336; https://doi.org/10.3390/cryst12101336 - 21 Sep 2022
Viewed by 1009
Abstract
The Hastelloy X superalloy is a widely used solid-solution Ni-based sheet alloy for gas turbines, aero-engine combustion chambers, and other hot-end components. To investigate the effect of microstructure, especially grain size, on its weldability, Hastelloy X alloy bars are homogenized, cold-rolled to thin [...] Read more.
The Hastelloy X superalloy is a widely used solid-solution Ni-based sheet alloy for gas turbines, aero-engine combustion chambers, and other hot-end components. To investigate the effect of microstructure, especially grain size, on its weldability, Hastelloy X alloy bars are homogenized, cold-rolled to thin sheets, and recrystallized under different conditions to obtain equiaxed grain microstructures with average grain sizes of ~5 μm, ~12 μm, and ~90 μm. The laser welding process is used for joining the alloy sheets, and then the alloy’s weldability is investigated through microstructural and mechanical property characterizations. The microstructures in weld consist of coarse columnar grains with dendrite, and grain sizes of these columnar grains are almost the same when grain size of Hastelloy X base metal increases from ~5 μm to ~90 μm. Moreover, although all welds exhibit lower yield strengths (YS), ultimate tensile strengths (UTS), and elongations to fracture (EF) than the base metal, the degrees of reduction in them become slight when the grain size of base metal increases from ~5 μm to ~90 μm. Full article
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Article
Effective Chiral Interactions between Nonchiral Rigid Macromolecules in a Chiral Solvent and the Induced Cholesteric Liquid Crystal Phase
Crystals 2022, 12(9), 1318; https://doi.org/10.3390/cryst12091318 - 18 Sep 2022
Cited by 1 | Viewed by 886
Abstract
It has been shown that a nonchiral anisotropic macromolecule embedded in a chiral dielectric solvent possesses an effective optical activity proportional to the optical activity of the solvent. As a result, there exists an effective chiral interaction between the macromolecules, which creates a [...] Read more.
It has been shown that a nonchiral anisotropic macromolecule embedded in a chiral dielectric solvent possesses an effective optical activity proportional to the optical activity of the solvent. As a result, there exists an effective chiral interaction between the macromolecules, which creates a torque acting on the primary axes of the two interacting molecules. A general expression for the effective chiral interaction potential has been derived in terms of the effective polarizability and the effective gyration tensor of the macromolecule in the chiral solvent. Explicit expressions for the components of the effective polarizability and the gyration have been obtained using the model of a hard rod filled with anisotropic dielectric and embedded into the isotropic chiral dielectric medium. The theory predicts the formation of the cholesteric helical structure in the nematic polymer liquid crystal phase induced by a chiral solvent. Full article
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Article
Selection Criterion of Stable Dendritic Growth for a Ternary (Multicomponent) Melt with a Forced Convective Flow
Crystals 2022, 12(9), 1288; https://doi.org/10.3390/cryst12091288 - 12 Sep 2022
Viewed by 803
Abstract
A stable growth mode of a single dendritic crystal solidifying in an undercooled ternary (multicomponent) melt is studied with allowance for a forced convective flow. The steady-state temperature, solute concentrations and fluid velocity components are found for two- and three-dimensional problems. The stability [...] Read more.
A stable growth mode of a single dendritic crystal solidifying in an undercooled ternary (multicomponent) melt is studied with allowance for a forced convective flow. The steady-state temperature, solute concentrations and fluid velocity components are found for two- and three-dimensional problems. The stability criterion and the total undercooling balance are derived accounting for surface tension anisotropy at the solid-melt interface. The theory under consideration is compared with experimental data and phase-field modeling for Ni98Zr1Al1 alloy. Full article
(This article belongs to the Special Issue Phase Transition in External Fields)
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Article
Chiral π-Conjugated Liquid Crystals: Impacts of Ethynyl Linker and Bilateral Symmetry on the Molecular Packing and Functions
Crystals 2022, 12(9), 1278; https://doi.org/10.3390/cryst12091278 - 09 Sep 2022
Viewed by 1136
Abstract
Recently, various chiral aromatic compounds, including chiral π-conjugated liquid crystals, have been developed for their unique photofunctions. One of the typical photofunctions is the bulk photovoltaic effect of ferroelectric π-conjugated liquid crystals, which integrates a polar environment based on molecular chirality with an [...] Read more.
Recently, various chiral aromatic compounds, including chiral π-conjugated liquid crystals, have been developed for their unique photofunctions. One of the typical photofunctions is the bulk photovoltaic effect of ferroelectric π-conjugated liquid crystals, which integrates a polar environment based on molecular chirality with an extended π-conjugation system. Tuning the spectral properties and molecular packing is essential for improving the optical functions of the chiral π-conjugated liquid crystals. Herein, we examined the effects of an ethynyl linker and bilateral symmetry on the liquid-crystalline (LC) properties and π-conjugated system through detailed characterization via polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction analysis. The spreading of the π-conjugated system was evaluated using UV–vis absorption and photoluminescence spectroscopy. Bilateral symmetry affects the LC and photoluminescent properties. Hetero-substitution with a sparse ethynyl linker likely allows the formation of an interdigitated smectic LC structure. Because the molecular packing and photophysical properties can affect the photo- and electrical functions, we believe this study can promote the molecular design of novel functional π-conjugated materials, such as chiral ferroelectric π-conjugated liquid crystals, exhibiting the bulk photovoltaic effect. Full article
(This article belongs to the Special Issue State-of-the-Art Liquid Crystals Research in Japan)
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Article
Synthesis and Magnetic Properties of Carbon Doped and Reduced SrTiO3 Nanoparticles
Crystals 2022, 12(9), 1275; https://doi.org/10.3390/cryst12091275 - 08 Sep 2022
Cited by 2 | Viewed by 1072
Abstract
We report on the studies of the synthesis, structural, and magnetic properties of undoped SrTiO3 (STO), carbon-doped STO:C, and reduced STO STO:R nanoparticles. Fine (~20–30 nm) and coarse (~100 nm) nanoparticles with a single phase of cubic perovskite-type structure were sintered by [...] Read more.
We report on the studies of the synthesis, structural, and magnetic properties of undoped SrTiO3 (STO), carbon-doped STO:C, and reduced STO STO:R nanoparticles. Fine (~20–30 nm) and coarse (~100 nm) nanoparticles with a single phase of cubic perovskite-type structure were sintered by thermal decomposition of SrTiO(C2O4)2. Magnetization loops of fine STO:C and STO:R nanoparticles at low temperatures and an almost linear decrease in magnetization with temperature indicate the realization of a soft, ferromagnetic state in them, with a pronounced disorder effect characteristic of doped dilute magnetic semiconductors. Oxidation and particle size increase suppress the magnetic manifestations, demonstrating the importance of surface-related defects and oxygen deficiency in the emergence of magnetism. It was found that oxygen vacancies and doping with carbon make similar contributions to the magnetization, while complementary electron paramagnetic resonance, together with magnetization measurement studies, show that the most probable state of oxygen vacancies, which determine the appearance of magnetic properties, are charged F+ oxygen vacancies and C-impurity centers, which tend to segregate on the surface of nanoparticles. Full article
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Article
Neural Network Solver for Small Quantum Clusters
Crystals 2022, 12(9), 1269; https://doi.org/10.3390/cryst12091269 - 06 Sep 2022
Cited by 2 | Viewed by 1065
Abstract
Machine learning approaches have recently been applied to the study of various problems in physics. Most of these studies are focused on interpreting the data generated by conventional numerical methods or the data on an existing experimental database. An interesting question is whether [...] Read more.
Machine learning approaches have recently been applied to the study of various problems in physics. Most of these studies are focused on interpreting the data generated by conventional numerical methods or the data on an existing experimental database. An interesting question is whether it is possible to use a machine learning approach, in particular a neural network, for solving the many-body problem. In this paper, we present a neural network solver for the single impurity Anderson model, the paradigm of an interacting quantum problem in small clusters. We demonstrate that the neural-network-based solver provides quantitative accurate results for the spectral function as compared to the exact diagonalization method. This opens the possibility of utilizing the neural network approach as an impurity solver for other many-body numerical approaches, such as the dynamical mean field theory. Full article
(This article belongs to the Special Issue New Spin on Metal-Insulator Transitions)
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Article
Ambient Pressure Synthesis of Re-Substituted MnGe and Its Magnetic Properties
Crystals 2022, 12(9), 1256; https://doi.org/10.3390/cryst12091256 - 05 Sep 2022
Viewed by 1102
Abstract
Due to their non-centrosymmetric structure, B20-type compounds have intriguing properties of chiral magnets and are the objects of study of topological spin textures. Among them is a high-pressure phase MnGe, which demonstrates properties of magnetic skyrmions. We report on the synthesis of an [...] Read more.
Due to their non-centrosymmetric structure, B20-type compounds have intriguing properties of chiral magnets and are the objects of study of topological spin textures. Among them is a high-pressure phase MnGe, which demonstrates properties of magnetic skyrmions. We report on the synthesis of an Mn1−xRexGe solid solution with the B20 structure, which can be prepared without the application of high pressure. Mn1−xRexGe (x = 0.169(6)) shows unconventional magnetic behavior, where the Neel temperature is only slightly reduced compared to a chiral-lattice helimagnet MnGe. Full article
(This article belongs to the Special Issue Feature Papers in Crystalline Metals and Alloys in 2022-2023)
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Article
Numerical Analysis of Gas Flow Instabilities in Simplified Vertical HVPE GaN Reactors
Crystals 2022, 12(9), 1248; https://doi.org/10.3390/cryst12091248 - 02 Sep 2022
Viewed by 1070
Abstract
This paper investigates the gas flow and the mass transport in simplified axial-symmetric vertical HVPE reactors for the growth of GaN bulk crystals through numerical simulations. We evaluate the relative significance of different flow and transport phenomena in dependence on the direction of [...] Read more.
This paper investigates the gas flow and the mass transport in simplified axial-symmetric vertical HVPE reactors for the growth of GaN bulk crystals through numerical simulations. We evaluate the relative significance of different flow and transport phenomena in dependence on the direction of gravity. The performed simulations show that buoyancy effects due to density differences between neighboring gas lines are the main factor causing the deformation of laminar flow patterns and the formation of recirculation cells within the growth zone. Baroclinic instabilities have been identified as the source for these phenomena. In contrast, typical vertical temperature gradients show only a minor impact on the stability of the gas flow within the growth zone in the vicinity of the growing crystal. Based on these results, major differences of the species transport in vertical HVPE reactors, where the flow is parallel or anti-parallel to the direction of gravity, referred to as down-flow and up-flow, respectively, are summarized. The performed analysis of the interplay and relative significance of different flow effects in the HVPE environment allows a general recommendation for reactor design and scaling with respect to stable gas flow conditions within the growth zone. Full article
(This article belongs to the Special Issue GaN-Based Materials and Devices)
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Article
Magnussonite, Mn2+18 (As3+O3)6Mn1+x(H2O, Clx, ☐): Re-Examination of the Structure and the [Mn1+(As3+O3)6] Cluster
Crystals 2022, 12(9), 1221; https://doi.org/10.3390/cryst12091221 - 29 Aug 2022
Viewed by 879
Abstract
The crystal structure of magnussonite, ideally Mn2+18[As3+6(Mn1+x)O18]2[(H2O, Clx, ☐) (H2O, ☐)]2, from Långban, Sweden, was refined to an R1-index of [...] Read more.
The crystal structure of magnussonite, ideally Mn2+18[As3+6(Mn1+x)O18]2[(H2O, Clx, ☐) (H2O, ☐)]2, from Långban, Sweden, was refined to an R1-index of 1.19% and the structure proposed by Moore and Araki (1979) is confirmed. Magnussonite has a densely packed structure of (Mnφn) polyhedra, φ = (O2−, H2O, Cl), and (As3+O3) triangular pyramids that is best envisaged as layers of polyhedra in the same way as many of the other manganese-arsenite-arsenate structures from Långban. There are two distinct layers in magnussonite; the two layers may be combined into a slab that stacks along the a-direction with rotations between adjacent slabs. A surprising feature of the dense-packed magnussonite atomic arrangement is an array of structural channels along [111] that contain much of the disorder that occurs in the magnussonite structure. The channels contain the partly occupied MX site on the central axis of the channel, and the CLW2 site (with extremely low occupancy), also on the central axis of the channel. The CLW2 site, previously unrecognized in the magnussonite structure, contains H2O, whereas the minor Cl in the structure resides in the CLW1 channel site, balancing the charge of the MX-site occupant. The MX site on the central axis of the channels displays a coordination known only in Långban minerals. In the local arrangement around the unoccupied MX site, the neighboring (As3+O3) groups project their associated stereoactive lone-pairs of electrons into the channel. Where the MX site is occupied by Mn, there are six lone-pairs of electrons pointing toward Mn; the 18-electron rule predicts/rationalizes formulae for this stable transition-metal cluster. The (As3+O3) groups and MX occupant form a [Mn+(As3+O3)6] arrangement in accord with the 18-electron rule where Mn+ contributes 6 3d electrons and the six lone-pairs of the [(As3+O3)6] arrangement contribute 12 electrons for a total of 18 electrons that form nine molecular orbitals that are metal-ligand bonds or non-bonding. Magnussonite and dixenite, another basic manganese-iron arsenate-arsenite-silicate mineral of the Långban-type deposits in Bergslagen, Sweden, are the only two minerals known with such local [M+(As3+O3)n] transition-metal clusters. The presence of these exotic clusters in structures containing densely packed Mn2+ octahedra is not understood at present. Full article
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Article
Shape-Controlled Crystal Growth of Y3Al5O12:Ce Single Crystals with Application of Micro-Pulling-Down Method and Mo Crucibles, and Their Scintillation Properties
Crystals 2022, 12(9), 1215; https://doi.org/10.3390/cryst12091215 - 28 Aug 2022
Viewed by 882
Abstract
The technology to grow single crystals of the required shape directly from a melt has been researched extensively and developed in various industries and research fields. In this study, a micro-pulling-down method and a Mo crucible were applied to the shape-controlled crystal growth [...] Read more.
The technology to grow single crystals of the required shape directly from a melt has been researched extensively and developed in various industries and research fields. In this study, a micro-pulling-down method and a Mo crucible were applied to the shape-controlled crystal growth of Y3Al5O12:Ce (YAG:Ce). Three types of Mo crucibles with different die shapes were developed. Stable crystal growth of more than 50 mm in length was achieved with the same shape as the die, and scintillation light output of ~20,000 ph/MeV, which is comparable with those of the YAG:Ce crystal grown by Cz method, were obtained. The transmittance of grown crystals above 500 nm was above 70%. The standard deviation (σ) of the scintillation light output at each position of the 50-mm-long sample was found to be within ±16%. Full article
(This article belongs to the Special Issue Novel Scintillator Crystals)
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Article
Enhanced THz Transmission by Bull’s Eye Structure Integrated with a Concentric Gold Hemisphere
Crystals 2022, 12(9), 1210; https://doi.org/10.3390/cryst12091210 - 27 Aug 2022
Viewed by 1137
Abstract
In this work, a hemispheric gold particle is introduced to the conventional bull’s eye structure that enhances extraordinary optical transmission in the terahertz region. Transmission enhancement is a result of the coupling of surface plasmon polaritons generated by periodic grooves and localized surface [...] Read more.
In this work, a hemispheric gold particle is introduced to the conventional bull’s eye structure that enhances extraordinary optical transmission in the terahertz region. Transmission enhancement is a result of the coupling of surface plasmon polaritons generated by periodic grooves and localized surface plasmon resonances generated by the hemisphere particle. The maximum normalized-to-area transmission peak reaches 556 for the hemisphere-in-hole bull’s eye structure, which is significantly higher than conventional bull’s eye structure. Such a transmission property is insensitive to polarization direction. The physical mechanisms are thoroughly analyzed by geometric parameter optimization and electromagnetic simulations. The modified structure can reduce the number of grooves in need, thereby reducing the device area. This novel design can be instructive for future improvement of bull’s eye applications. Full article
(This article belongs to the Special Issue Terahertz Metamaterials and Active Modulation)
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Article
Saturation Spectroscopic Studies on Yb3+ and Er3+ Ions in Li6Y(BO3)3 Single Crystals
Crystals 2022, 12(8), 1151; https://doi.org/10.3390/cryst12081151 - 16 Aug 2022
Viewed by 795
Abstract
The results of a series of pump–probe spectral hole-burning experiments are presented on Yb3+- or Er3+-doped Li6Y(BO3)3 (LYB) single crystals in the temperature range of 2–14 K and 9–28 K, respectively. The spectral hole [...] Read more.
The results of a series of pump–probe spectral hole-burning experiments are presented on Yb3+- or Er3+-doped Li6Y(BO3)3 (LYB) single crystals in the temperature range of 2–14 K and 9–28 K, respectively. The spectral hole has a complex structure for Yb3+ with superposed narrow and broad bands, while a single absorption hole has been observed for Er3+. Population relaxation times (T1) at about 850 ± 60 μs and 1010 ± 50 μs and dipole relaxation times (T2) with values of 1100 ± 120 ns and 14.2 ± 0.3 ns have been obtained for the two components measured for the Yb3+:2F7/22F5/2 transition. T1 = 402 ± 8 μs and T2 = 11.9 ± 0.2 ns values have been found for the Er3+:4I15/24I11/2 excitation. The spectral diffusion rate at about 1 and 5 MHz/ms has been determined for the narrow and broad spectral line in Yb3+-doped crystal, respectively. The temperature dependence of the spectral hole halfwidth has also been investigated. Full article
(This article belongs to the Special Issue Optical and Spectroscopic Properties of Rare-Earth-Doped Crystals)
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Article
First-Principles Calculations of the Structural, Electronic, Optical, and Mechanical Properties of 21 Pyrophosphate Crystals
Crystals 2022, 12(8), 1139; https://doi.org/10.3390/cryst12081139 - 12 Aug 2022
Cited by 1 | Viewed by 1136
Abstract
Pyrophosphate crystals have a wide array of applications in industrial and biomedical fields. However, fundamental understanding of their electronic structure, optical, and mechanical properties is still scattered and incomplete. In the present research, we report a comprehensive theoretical investigation of 21 pyrophosphates A [...] Read more.
Pyrophosphate crystals have a wide array of applications in industrial and biomedical fields. However, fundamental understanding of their electronic structure, optical, and mechanical properties is still scattered and incomplete. In the present research, we report a comprehensive theoretical investigation of 21 pyrophosphates A2M (H2P2O7)2•2H2O with either triclinic or orthorhombic crystal structure. The molecule H2P2O7 is the dominant molecular unit, whereas A = (K, Rb, NH4, Tl), M = (Zn, Cu, Mg, Ni, Co, Mn), and H2O stand for the cation elements, transition metals, and the water molecules, respectively. The electronic structure, interatomic bonding, partial charge distribution, optical properties, and mechanical properties are investigated by first-principles calculations based on density functional theory (DFT). Most of these 21 crystals are theoretically investigated for the first time. The calculated results show a complex interplay between A, M, H2P2O7, and H2O, resulting in either metallic, half-metallic, or semi-conducting characteristics. The novel concept of total bond order density (TBOD) is used as a single quantum mechanical metric to characterize the internal cohesion of these crystals to correlate with the calculated properties, especially the mechanical properties. This work provides a large database for pyrophosphate crystals and a road map for potential applications of a wider variety of phosphates. Full article
(This article belongs to the Topic First-Principles Simulation—Nano-Theory)
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Article
Ab-Initio Study of Calcium Fluoride Doped with Heavy Isotopes
Crystals 2022, 12(8), 1128; https://doi.org/10.3390/cryst12081128 - 11 Aug 2022
Viewed by 1058
Abstract
Precision laser spectroscopy of the 229-thorium nuclear isomer transition in a solid-state environment would represent a significant milestone in the field of metrology, opening the door to the realization of a nuclear clock. Working toward this goal, experimental methods require knowledge of various [...] Read more.
Precision laser spectroscopy of the 229-thorium nuclear isomer transition in a solid-state environment would represent a significant milestone in the field of metrology, opening the door to the realization of a nuclear clock. Working toward this goal, experimental methods require knowledge of various properties of a large band-gap material, such as calcium fluoride doped with specific isotopes of the heavy elements thorium, actinium, cerium, neptunium, and uranium. By accurately determining the atomic structure of potential charge compensation schemes by using a generalized gradient approximation within the ab-initio framework of density functional theory, calculations of electric field gradients on the dopants become accessible, which cause a quadrupole splitting of the nuclear-level structure that can be probed experimentally. Band gaps and absorption coefficients in the range of the 229-thorium nuclear transition are estimated by using the G0W0 method and by solving the Bethe–Salpeter equation. Full article
(This article belongs to the Special Issue Defects in Crystals)
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