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 authors, or important in this field. 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
The Indentation Size Effect (ISE) of Metals
Crystals 2022, 12(6), 795; https://doi.org/10.3390/cryst12060795 - 02 Jun 2022
Abstract
The literature regarding the Reverse Indentation Size Effect (RISE) is scarce, the occurrence of which is assumed for plastic materials, including metals. The content of this article is to study the relationship between applied load and measured values of the Vickers micro-hardness of [...] Read more.
The literature regarding the Reverse Indentation Size Effect (RISE) is scarce, the occurrence of which is assumed for plastic materials, including metals. The content of this article is to study the relationship between applied load and measured values of the Vickers micro-hardness of 19 metals with different types of lattices, measured with a Hanemann tester. The values of the load ranged between 0.09807 N (10 g) and 0.9807 N (100 g). The size and character of the Indentation Size Effect (ISE) were evaluated by Meyer’s power law (index n), Proportional Specimen Resistance (PSR), and Hays—Kendall methods. Meyer’s index n ranged between 1.65 for Mo and 2.44 for Ni. A correlation was found between the micro-hardness and Meyer’s index for metals with FCC and HCP lattices. The measured value of Vickers micro-hardness is influenced by the size and nature of the ISE. If this is not taken into account, it may be misleading. For this reason, we recommend using the “true hardness”, determined by the presented method. Full article
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Article
Weak Antilocalization in Polycrystalline SnTe Films Deposited by Magnetron Sputtering
Crystals 2022, 12(6), 773; https://doi.org/10.3390/cryst12060773 - 26 May 2022
Abstract
Previous works on weak antilocalization (WAL) of SnTe were mostly carried out in MBE-grown films, where the signals of WAL usually coexist with a large parabolic background of classical magnetoresistance. In this article, we present our study on WAL in polycrystalline SnTe films [...] Read more.
Previous works on weak antilocalization (WAL) of SnTe were mostly carried out in MBE-grown films, where the signals of WAL usually coexist with a large parabolic background of classical magnetoresistance. In this article, we present our study on WAL in polycrystalline SnTe films deposited by magnetron sputtering. Due to the polycrystalline nature and the relatively low mobility of the films, the background of conventional magnetoresistance was greatly suppressed, and clean WAL signals, which are well described by the Hikami–Larkin–Nagaoka equation, were obtained at low temperatures. A close analysis of the WAL data shows that the number of transport channels contributing to WAL increases monotonously with decreasing temperatures, reaching N=2.8 at T=1.6 K in one of the devices, which indicates the decoupling of Dirac cones at low temperatures. Meanwhile, as the temperature decreases, the temperature dependence of phase coherence length gradually changes from lϕT1 to lϕT0.5, suggesting that the dominant mechanism of phase decoherence switches from electron–phonon scattering to electron–electron scattering. Our results are helpful for understanding the quantum transport properties of SnTe. Full article
(This article belongs to the Special Issue Topological Materials)
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Article
Metal-Organic Framework vs. Coordination Polymer—Influence of the Lanthanide on the Nature of the Heteroleptic Anilate/Terephtalate 3D Network
Crystals 2022, 12(6), 763; https://doi.org/10.3390/cryst12060763 - 26 May 2022
Abstract
Metal-organic frameworks (MOFs), whose definition has been regularly debated, are a sub-class of coordination polymers (CPs) which may feature both an overall 3D architecture and some degree of porosity. In this context, MOFs based on lanthanides (Ln-MOFs) could find many applications due to [...] Read more.
Metal-organic frameworks (MOFs), whose definition has been regularly debated, are a sub-class of coordination polymers (CPs) which may feature both an overall 3D architecture and some degree of porosity. In this context, MOFs based on lanthanides (Ln-MOFs) could find many applications due to the combination of sorption properties and magnetic/luminescent behaviors. Here we report rare examples of 3D Ln-CPs based on anilate linkers, obtained under solvothermal conditions using a heteroleptic strategy. The three compounds of formula [Yb2(μ-ClCNAn)2(μ-F4BDC)(H2O)4]·(H2O)3 (1), [Er2(μ-ClCNAn)2(μ-F4BDC)(H2O)4]·(H2O)4 (2) and [Eu2(μ-ClCNAn)2(μ-F4BDC)(H2O)6] (3) have been characterized by single-crystal X-ray diffraction, thermogravimetric analysis, and optical measurements. Structural characterization revealed that compounds 1 and 2 present an interesting MOF architecture with extended rectangular cavities which are only filled with water molecules. On the other hand, compound 3 shows a much more complex topology with no apparent cavities. We discuss here the origins of such differences and highlight the crucial role of the Ln(III) ion nature for the topology of the CP. Compounds 1 and 2 now offer a playground to investigate the possible synergy between gas/solvent sorption and magnetic/luminescent properties of Ln-MOFs. Full article
(This article belongs to the Special Issue Luminescence and Magnetism in Lanthanide-Based Coordination Polymers)
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Article
Flux Method Growth and Structure and Properties Characterization of Rare-Earth Iron Oxides Lu1−xScxFeO3 Single Crystals
Crystals 2022, 12(6), 769; https://doi.org/10.3390/cryst12060769 - 26 May 2022
Abstract
Perovskite rare-earth ferrites (REFeO3) have attracted great attention for their high ferroelectric and magnetic transition temperatures, strong magnetoelectric coupling, and electric polarization. We report on the flux method growth of rare-earth iron oxide Lu1−xScxFeO3 single crystals [...] Read more.
Perovskite rare-earth ferrites (REFeO3) have attracted great attention for their high ferroelectric and magnetic transition temperatures, strong magnetoelectric coupling, and electric polarization. We report on the flux method growth of rare-earth iron oxide Lu1−xScxFeO3 single crystals through a K2CO3-B2O3-Bi2O3 mixture as a flux solution, and give a detailed characterization of the microstructure, magnetism, and ferroelectric properties. X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) measurements revealed that the obtained single crystals can be designated to three different crystal structures of different chemical compositions, that is, Lu0.96Sc0.04FeO3 (perovskite phase), Lu0.67Sc0.33FeO3 (hexagonal phase), and Lu0.2Sc0.8FeO3 (bixbyite phase), respectively. Magnetic measurements indicate that the perovskite Lu0.96Sc0.04FeO3 is an anisotropic hard ferromagnetic material with a high Curie transition temperature, the bixbyite Lu0.2Sc0.8FeO3 is a low temperature soft ferromagnetic material, and the hexagonal Lu0.67Sc0.33FeO3 exhibits multiferroic properties. Lu0.67Sc0.33FeO3 possesses a weak ferromagnetic transition at about 162 K. We further investigate the ferroelectric domain structures in hexagonal sample by scanning electron microscope and the characteristic atomic structures in ferroelectric domain walls by atomically resolved scanning transmission electron microscope. Our successful growth of perovskite Lu1−xScxFeO3 single crystals with distinct crystal structures and stochiometric Lu-Sc substitutions is anticipated to provide a useful ferrites system for furthering exploitation of their multiferroic properties and functionalities. Full article
(This article belongs to the Special Issue Topological Materials)
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Article
First High-Resolution Crystal Structures of DNA:2′-O-Methyl-RNA Heteroduplexes
Crystals 2022, 12(6), 760; https://doi.org/10.3390/cryst12060760 - 25 May 2022
Abstract
Heteroduplexes composed of all-DNA and all-2′-OMe RNA strands do not occur in nature, but they have found application in the development of molecular beacons and could also be used as aptamers or elements of nucleic acid-based nanostructures that will contain such structural motifs. [...] Read more.
Heteroduplexes composed of all-DNA and all-2′-OMe RNA strands do not occur in nature, but they have found application in the development of molecular beacons and could also be used as aptamers or elements of nucleic acid-based nanostructures that will contain such structural motifs. The crystallization experiments performed have shown that the introduction of overhangs at the ends of the duplex has a great influence on the success of crystallization, as well as on the DNA:2′-OMe-RNA heteroduplex crystal packing. The molecular and crystal structure of the DNA:2′-O-methyl-RNA heteroduplex in its overhanging and blunt-ended versions was determined at 100 K using synchrotron radiation with a resolution of 1.91 and 1.55 Å, respectively. The Zn-SAD method was used to resolve the original duplex structure when molecular replacement by many existing models of duplex structures failed. Both molecules analyzed adopted a conformation close to the A-RNA double helix. The presented structures provide the first insight into this type of heteroduplexes and allowed a comparative analysis with existing nucleic acid homo- and heteroduplex structures. The results of our research expand the knowledge of the structural properties of new heteroduplexes and may be useful for future applications, such as therapies using this class of compounds. Full article
(This article belongs to the Special Issue Nucleic Acid Crystallography)
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Article
Effect of Cooling Rate on Nano-Eutectic Formation in Laser Surface Remelted and Rare Earth Modified Hypereutectic Al-20Si Alloys
Crystals 2022, 12(5), 750; https://doi.org/10.3390/cryst12050750 - 23 May 2022
Abstract
Laser Surface Remelting (LSR) was applied to arc-melted Al-20Si-0.2Sr, Al-20Si-0.2Ce, and Al-20Si hypereutectic alloys to refine microstructures. Experiments revealed that microstructures in the melt pool varied from fully eutectic to a mixture of Al dendrites and inter-dendritic eutectic. We calculated cooling rates using [...] Read more.
Laser Surface Remelting (LSR) was applied to arc-melted Al-20Si-0.2Sr, Al-20Si-0.2Ce, and Al-20Si hypereutectic alloys to refine microstructures. Experiments revealed that microstructures in the melt pool varied from fully eutectic to a mixture of Al dendrites and inter-dendritic eutectic. We calculated cooling rates using the Eagar-Tsai model and correlated cooling rates with characteristic microstructures, revealing that a cooling rate on the order of 104 K/s could lead to maximized fully eutectic microstructure morphology. Due to rapid solidification, the Si composition in the LSR eutectic was measured at 18.2 wt.%, higher than the equilibrium eutectic composition of 12.6 wt.%Si. Compared to Al-20Si, Ce addition had no significant effect on the volume fraction of the fully eutectic structure but refined Si fibers to approximately 30 nm in diameter. Sr addition did not further refine the diameter of eutectic Si fibers compared to Al-20Si but increased the volume fraction of the fully eutectic microstructure morphology. The refinement ratio (φ) of the Si fiber diameter from the bottom of the melt pool to the surface for the three alloys was similar, at around 28%. The established correlation between the cooling rate and the size and morphology of the microstructure within the melt pool will enable tailoring of the microstructure in laser-processed as well as deposited alloys for high strength and plasticity. Full article
(This article belongs to the Special Issue Structure and Properties of Nanocrystalline Metallic Materials)
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Article
Crystal Growth and Characterization of ZrSiS-Type Topological Dirac Semimetals
Crystals 2022, 12(5), 728; https://doi.org/10.3390/cryst12050728 - 19 May 2022
Abstract
WHM materials (W = Zr/Hf, H = Si/Ge/Sn, M = S/Se/Te) represent a large family of topological semimetals, which have attracted intensive interest since they are considered to be good candidates for studying various topological states. Here, we report the crystal growth, characterization, [...] Read more.
WHM materials (W = Zr/Hf, H = Si/Ge/Sn, M = S/Se/Te) represent a large family of topological semimetals, which have attracted intensive interest since they are considered to be good candidates for studying various topological states. Here, we report the crystal growth, characterization, and electronic properties of HfSiS, ZrGeS, and ZrGeSe. All samples were prepared by a chemical vapor transport method with I2 as a transport agent, and the growth conditions were optimized. X-ray diffraction (XRD) measurements showed that the as-grown crystals crystallized in a PbFCl-type layered structure. They all showed metallic behavior from temperature-dependent resistivity measurements and the carrier densities were estimated to be in the order of 1021 cm−3. A large magnetoresistance of up to 1200% and an obvious Shubnikov–de Hass (SdH) oscillation were observed for HfSiS. Full article
(This article belongs to the Section Inorganic Crystalline Materials)
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Article
Elucidation of the Conformational Transition of Oligopeptidase B by an Integrative Approach Based on the Combination of X-ray, SAXS, and Essential Dynamics Sampling Simulation
Crystals 2022, 12(5), 712; https://doi.org/10.3390/cryst12050712 - 17 May 2022
Abstract
Oligopeptidase B (OPB) is the least studied group from the prolyl oligopeptidase family. OPBs are found in bacteria and parasitic protozoa and represent pathogenesis factors of the corresponding infections. OPBs consist of two domains connected by a hinge region and have the characteristics [...] Read more.
Oligopeptidase B (OPB) is the least studied group from the prolyl oligopeptidase family. OPBs are found in bacteria and parasitic protozoa and represent pathogenesis factors of the corresponding infections. OPBs consist of two domains connected by a hinge region and have the characteristics of conformational dynamics, which include two types of movements: the bridging/separation of α/β-hydrolase catalytic and β-propeller-regulatory domains and the movement of a loop carrying catalytic histidine, which regulates an assembly/disassembly of the catalytic triad. In this work, an elucidation of the interdomain dynamics of OPB from Serratia proteamaculans (SpOPB) with and without modification of the hinge region was performed using a combination of X-ray diffraction analysis and small-angle X-ray scattering, which was complemented with an essential dynamics sampling (EDS) simulation. The first crystal structure of catalytically deficient SpOPB (SpOPBS532A) with an intact hinge sequence is reported. Similarly to SpOPB with modified hinges, SpOPBS532A was crystallized in the presence of spermine and adopted an intermediate conformation in the crystal lattice. Despite the similarity of the crystal structures, a difference in the catalytic triad residue arrangement was detected, which explained the inhibitory effect of the hinge modification. The SpOPBS532A structure reconstituted to the wild-type form was used as a starting point to the classical MD followed by EDS simulation, which allowed us to simulate the domain separation and the transition of the enzyme from the intermediate to open conformation. The obtained open state model was in good agreement with the experimental SAXS data. Full article
(This article belongs to the Special Issue Protein Crystallography: Achievements and Challenges)
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Article
High-Rate Crystal/Polycrystal Dislocation Dynamics
Crystals 2022, 12(5), 705; https://doi.org/10.3390/cryst12050705 - 16 May 2022
Abstract
The present report builds upon work recently published on crystal and polycrystal dislocation mechanics behaviors assessed, in part, in split-Hopkinson pressure bar (SHPB) and shock loading investigations. A connection between the flow stress dependencies on strain rate in the different tests had been [...] Read more.
The present report builds upon work recently published on crystal and polycrystal dislocation mechanics behaviors assessed, in part, in split-Hopkinson pressure bar (SHPB) and shock loading investigations. A connection between the flow stress dependencies on strain rate in the different tests had been established in the previous report, whereas additional results are assessed here for (1) relationship of the measurements to a nano-scale prismatic dislocation structure proposed to be generated at a propagating shock front and (2) further relationships between the modeled structure and corresponding thermal stress and strain rate sensitivity computations, including new evaluations of the engineering rate sensitivity parameter, m = [∆lnσ/∆ln(dε/dt)]T. A comparison is made of m values approaching 1.0 for simulated dislocation mechanics results computed for tantalum crystals. Other (lower) m value comparisons involve recently determined higher shock stress measurements made on copper material at higher temperatures. Full article
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Article
Characterizations of Single-Crystal Lithium Niobate Thin Films
Crystals 2022, 12(5), 667; https://doi.org/10.3390/cryst12050667 - 06 May 2022
Abstract
Single-crystal lithium niobate thin films (lithium niobate on insulator, LNOI) are becoming a new material platform for integrating photonics. Investigation into the physical properties of LNOI is important for the design and fabrication of photonic devices. Herein, LNOIs were prepared by two methods: [...] Read more.
Single-crystal lithium niobate thin films (lithium niobate on insulator, LNOI) are becoming a new material platform for integrating photonics. Investigation into the physical properties of LNOI is important for the design and fabrication of photonic devices. Herein, LNOIs were prepared by two methods: ion implantation and wafer bonding; and wafer bonding and grinding. High-resolution X-ray diffraction (HRXRD) and confocal Raman spectroscopy were used to study the LNOI lattice properties. The full-width at half-maximum (FWHM) of HRXRD and Raman spectra showed a regular crystal lattice arrangement of the LNOIs. The domain inversion voltage and electro-optical coefficient of the LNOIs were close to those of LN bulk material. This study provides useful information for LNOI fabrication and for photonic devices in LNOI. Full article
(This article belongs to the Topic Optoelectronic Materials)
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Article
Simulation of Amorphous Silicon Carbide Photonic Crystal Absorption Layer for Solar Cells
Crystals 2022, 12(5), 665; https://doi.org/10.3390/cryst12050665 - 05 May 2022
Abstract
In this work, the amorphous silicon carbide (a-SiC) with low cost and high extinction coefficient was used as the light absorption layer of solar cells, and the photonic crystal (PC) structure and defect structure were introduced. By optimizing the scatterer shape, structural parameters [...] Read more.
In this work, the amorphous silicon carbide (a-SiC) with low cost and high extinction coefficient was used as the light absorption layer of solar cells, and the photonic crystal (PC) structure and defect structure were introduced. By optimizing the scatterer shape, structural parameters and defect types of photonic crystal, the absorption efficiency of the light absorption layer was further improved. The results show that the photonic crystal absorption layer with vacancy line defect is better than the perfect photonic crystal absorption layer. Meanwhile, the absorption efficiency of the photonic crystal absorption layer significantly improves in the case that the scatterer is an elliptical cylindrical air hole scatterer. When the incident light is in the wavelength range of 0.30~0.80 μm and the absorption layer height is 0.60 μm, the absorption efficiency of the absorption layer can reach 95.60%. Compared with the absorption layer without photonic crystal structure, the absorption layer is increased by 43.24%. At the same time, the absorption layer has little dependence on the incidence angle of sunlight. When the incidence angle is 65°, the absorption efficiency is still higher than 80%. Full article
(This article belongs to the Special Issue Frontiers of Perovskite Solar Cells)
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Article
Fingerprints of Topotactic Hydrogen in Nickelate Superconductors
Crystals 2022, 12(5), 656; https://doi.org/10.3390/cryst12050656 - 04 May 2022
Abstract
Superconductivity has entered the nickel age marked by enormous experimental and theoretical efforts. Notwithstanding, synthesizing nickelate superconductors remains extremely challenging, not least due to incomplete oxygen reduction and topotactic hydrogen. Here, we present density-functional theory calculations for nickelate superconductors with additional topotactic hydrogen [...] Read more.
Superconductivity has entered the nickel age marked by enormous experimental and theoretical efforts. Notwithstanding, synthesizing nickelate superconductors remains extremely challenging, not least due to incomplete oxygen reduction and topotactic hydrogen. Here, we present density-functional theory calculations for nickelate superconductors with additional topotactic hydrogen or oxygen, namely La1xSrxNiO2Hδ and LaNiO2+δ. We identify a phonon mode as a possible indication for topotactic hydrogen and discuss the charge redistribution patterns around oxygen and hydrogen impurities. Full article
(This article belongs to the Special Issue New Spin on Metal-Insulator Transitions)
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Article
Deformation Mechanism and Structural Changes in the Globular Ti-6Al-4V Alloy under Quasi-Static and Dynamic Compression: To the Question of the Controlling Phase in the Deformation of α+β Titanium Alloys
Crystals 2022, 12(5), 645; https://doi.org/10.3390/cryst12050645 - 01 May 2022
Abstract
The deformation mechanism of the Ti-6Al-4V (wt.%) alloy with globular structure was studied under conditions of quasi-static and high-strain compression with rates 10−3 s−1 and 2.1–3.3 × 103 s−1, respectively. High-strain compression was conducted using a Split Hopkinson [...] Read more.
The deformation mechanism of the Ti-6Al-4V (wt.%) alloy with globular structure was studied under conditions of quasi-static and high-strain compression with rates 10−3 s−1 and 2.1–3.3 × 103 s−1, respectively. High-strain compression was conducted using a Split Hopkinson Pressure Bar (SHPB). The details of the deformation mechanism were evaluated based on the analysis of the deformation hardening curves using the strain hardening exponent concept developed for titanium alloys in tension conditions. The used approach allowed us to identify the stages of plastic deformation observed and the controlling phase in deformation of two-phase alloy through the assessment of the strengthening index, n. It has been found that three deformation stages can be identified in quasi-static conditions. However, when the alloy is compressed at a high strain rate, the third deformation stage does not develop due to the high process rate. Further analysis of deformation curves reveals the leading role of the β-phase under the quasi-static conditions and the essential contribution of the second, α-phase, at a high compression rate. The findings on the deformation mechanism based on the analysis of hardening curves were supported by a detailed structural study. Full article
(This article belongs to the Special Issue Microstructure Characterization and Design of Alloys)
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Article
The Growth of High-Quality Hexagonal GaTe Nanosheets Induced by ZnO Nanocrystals
Crystals 2022, 12(5), 627; https://doi.org/10.3390/cryst12050627 - 27 Apr 2022
Abstract
The monoclinic and hexagonal gallium tellurides (m-GaTe and h-GaTe) show different applications in optoelectronic devices. Compared to the m-GaTe, the h-GaTe is a metastable phase, which generally exists in ultrathin samples and is difficult to obtain by direct [...] Read more.
The monoclinic and hexagonal gallium tellurides (m-GaTe and h-GaTe) show different applications in optoelectronic devices. Compared to the m-GaTe, the h-GaTe is a metastable phase, which generally exists in ultrathin samples and is difficult to obtain by direct chemical reaction. Herein, a hexagonal ZnO-induced crystal growth strategy was used for the design and fabrication of h-GaTe. The high-quality h-GaTe nanosheets were successfully grown on the (001) surface of hexagonal ZnO by the chemical vapor deposition method under ambient pressure. The SEM, XPS, XRD, and HRTEM characterizations uncovered a flower-like nanosheet morphology and a hexagonal crystal structure for the obtained GaTe samples. Meanwhile, the conductive atomic force microscope measurement indicates that the obtained h-GaTe nanosheet is a p-type semiconductor. Based on the electron localization function simulation, the lattice-induced crystal growth of h-GaTe was demonstrated. The results give an insight into the synthesis of metastable phase crystal and open an avenue for fabricating new two-dimensional devices by p-type h-GaTe. Full article
(This article belongs to the Special Issue Research on Two-Dimensional Materials and Devices)
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Article
Homogenization of Complex Lattices for Metamaterials: Open Problems and Conjectures
Crystals 2022, 12(5), 612; https://doi.org/10.3390/cryst12050612 - 26 Apr 2022
Abstract
Based on concrete examples dealing with one-level periodic and quasi-periodic, and two-level periodic lattices, we show that the homogenization of complex lattices generically requires a multi-field continuum approach. We do not present results for specific cases, rather we discuss some related open problems [...] Read more.
Based on concrete examples dealing with one-level periodic and quasi-periodic, and two-level periodic lattices, we show that the homogenization of complex lattices generically requires a multi-field continuum approach. We do not present results for specific cases, rather we discuss some related open problems and formulate pertinent conjectures. In this way, we suggest in essence a possible research program addressed towards the design of metamaterials. Full article
(This article belongs to the Special Issue Advances in Metamaterials)
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Article
Radiation Modification of Optical Characteristics of LiNbO3:Zn and LiNbO3:Mg Crystals
Crystals 2022, 12(5), 600; https://doi.org/10.3390/cryst12050600 - 25 Apr 2022
Abstract
The modification of the optical characteristics of LiNbO3:Zn and LiNbO3:Mg crystals grown by the Czochralski method was investigated using β and γ radiation. The photorefractive effect was found to be inhibited by ionizing radiation in the LiNbO3:Zn [...] Read more.
The modification of the optical characteristics of LiNbO3:Zn and LiNbO3:Mg crystals grown by the Czochralski method was investigated using β and γ radiation. The photorefractive effect was found to be inhibited by ionizing radiation in the LiNbO3:Zn ([ZnO] ≈ 2.1 mol%) crystal, which belonged to a below-threshold concentration range. The inhibition was attributed to a stepwise radiation annealing of charged defects. Ionizing radiation increased the general optical uniformity of above-threshold crystals LiNbO3:Zn ([ZnO] ≈ 5.9 mol%) and LiNbO3:Mg([MgO] ≈ 5.6 mol%). In addition, we determined that radiation annealing substantially influenced photorefraction dynamics in lightly doped LiNbO3:Zn ([ZnO] ≈ 0.1 mol%) crystals, which widens their application areas. Full article
(This article belongs to the Special Issue Optoelectronics and Photonics in Crystals)
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Article
Effect of Hydrogen Migration in SiO2/Al2O3 Stacked Gate Insulator of InGaZnO Thin-Film Transistors
Crystals 2022, 12(5), 594; https://doi.org/10.3390/cryst12050594 - 23 Apr 2022
Abstract
In this work, the correlation between SiO2 deposition thickness and hydrogen content is discussed and the effect of the SiO2 layer on the properties of synaptic InGaZnO (IGZO) TFTs is analyzed. Three types of IGZO synaptic thin-film transistors (TFTs) were fabricated [...] Read more.
In this work, the correlation between SiO2 deposition thickness and hydrogen content is discussed and the effect of the SiO2 layer on the properties of synaptic InGaZnO (IGZO) TFTs is analyzed. Three types of IGZO synaptic thin-film transistors (TFTs) were fabricated with different gate insulators, and the effect of SiO2 as a gate insulator was investigated. XPS analysis confirmed that the hydrogen content in the Al2O3 and SiO2 layers increased during SiO2 deposition step for all depth regions. Hydrogen injected by the SiO2 layer deposition step was confirmed to improve the memory window through more threshold voltage shift under positive bias stress (PBS) and negative bias stress (NBS) conditions. In addition, the retention characteristics were improved due to the low hydrogen movement velocity in the SiO2 layer. These results contribute to the optimization of the amount of hydrogen, and the proposed device has potential as a synaptic device capable of neuromorphic computing. Full article
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Article
Synthesis, X-ray, Hirshfeld, and AIM Studies on Zn(II) and Cd(II) Complexes with Pyridine Ligands
Crystals 2022, 12(5), 590; https://doi.org/10.3390/cryst12050590 - 22 Apr 2022
Abstract
The synthesis and crystal structures of three heteroleptic complexes of Zn(II) and Cd(II) with pyridine ligands (ethyl nicotinate (EtNic), N,N-diethylnicotinamide (DiEtNA), and 2-amino-5-picoline (2Ampic) are presented. The complex [Zn(EtNic)2Cl2] (1) showed [...] Read more.
The synthesis and crystal structures of three heteroleptic complexes of Zn(II) and Cd(II) with pyridine ligands (ethyl nicotinate (EtNic), N,N-diethylnicotinamide (DiEtNA), and 2-amino-5-picoline (2Ampic) are presented. The complex [Zn(EtNic)2Cl2] (1) showed a distorted tetrahedral coordination geometry with two EtNic ligand units and two chloride ions as monodentate ligands. Complexes [Zn(DiEtNA)(H2O)4(SO4)]·H2O (2) and [Cd(OAc)2(2Ampic)2] (3) had hexa-coordinated Zn(II) and Cd(II) centers. In the former, the Zn(II) was coordinated with three different monodentate ligands, which were DiEtNA, H2O, and SO42−. In 3, the Cd(II) ion was coordinated with two bidentate acetate ions and two monodentate 2Ampic ligand units. The supramolecular structures of the three complexes were elucidated using Hirshfeld analysis. In 1, the most important interactions that governed the molecular packing were O···H (15.5–15.6%), Cl···H (13.6–13.8%), Cl···C (6.3%), and C···H (10.3–10.6%) contacts. For complexes 2 and 3, the H···H, O···H, and C···H contacts dominated. Their percentages were 50.2%, 41.2%, and 7.1%, respectively, for 2 and 57.1%, 19.6%, and 15.2%, respectively, for 3. Only in complex 3, weak π-π stacking interactions between the stacked pyridines were found. The Zn(II) natural charges were calculated using the DFT method to be 0.8775, 1.0559, and 1.2193 for complexes 13, respectively. A predominant closed-shell character for the Zn–Cl, Zn–N, Zn–O, Cd–O, and Cd–N bonds was also concluded from an atoms in molecules (AIM) study. Full article
(This article belongs to the Special Issue New Trends in Crystals at Saudi Arabia (Volume II))
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Article
Pressure Induced Superconductivity and Multiple Structural Transitions in CsCl-Type Cubic CeZn Single Crystal
Crystals 2022, 12(5), 571; https://doi.org/10.3390/cryst12050571 - 20 Apr 2022
Abstract
CsCl-type cubic compound CeZn exhibits a paramagnetic (PM) to antiferromagnetic (AFM) first-order transition at TN ~ 30 K accompanied by a simultaneous structural transition from cubic to tetragonal structure as temperature decreases. Applying the pressure, the coupled magnetic and crystal structural transition [...] Read more.
CsCl-type cubic compound CeZn exhibits a paramagnetic (PM) to antiferromagnetic (AFM) first-order transition at TN ~ 30 K accompanied by a simultaneous structural transition from cubic to tetragonal structure as temperature decreases. Applying the pressure, the coupled magnetic and crystal structural transition becomes separated above 1.0 GPa and then the AFM order changes to ferromagnetic (FM). The FM ordering temperature decreases with further applying pressure and changes to a nonmagnetic state above ~3.0 GPa. In the nonmagnetic state, we discovered superconductivity below Tsc ~ 1.3 K over 5.5 GPa, which survives even up to 9.5 GPa. Investigation of single crystal X-ray diffraction at room temperature reveals that CeZn undergoes a sequential crystal structural change with increasing pressure from cubic at ambient pressure to the monoclinic structure at 8.2 GPa via tetragonal and orthorhombic structure. The detailed analysis of crystal structure in CeZn single crystal evidenced that the emergence of superconductivity is related to the orthorhombic-to-monoclinic transition implying a nonmagnetic origin of the Cooper pair formation. Full article
(This article belongs to the Special Issue Superconductors: Materials, Microstructures and Applications)
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Article
Evaluation of the Structural Deviation of Cu/Cu2O Nanocomposite Using the X-ray Diffraction Analysis Methods
Crystals 2022, 12(4), 566; https://doi.org/10.3390/cryst12040566 - 18 Apr 2022
Abstract
We successfully synthesized Cu/Cu2O nanocomposites using the wet chemical synthesis method. All X-ray diffraction (XRD), Reference Intensity Ratio (RIR), and Rietveld refinement methods confirmed that the compounds Cu and Cu2O are free of impurities. Scanning Electron Microscope (SEM) and [...] Read more.
We successfully synthesized Cu/Cu2O nanocomposites using the wet chemical synthesis method. All X-ray diffraction (XRD), Reference Intensity Ratio (RIR), and Rietveld refinement methods confirmed that the compounds Cu and Cu2O are free of impurities. Scanning Electron Microscope (SEM) and Transmission electron microscopy (TEM) images show the morphology and interactions of Cu and Cu2O in the structure. The formation mechanism is also explained by five stages: precursor, nucleation, growth, aging, and reduction. The changes in crystallization parameters under variations in reaction temperature (Tv) and stirring speed (Sv) were confirmed by agreement with the XRD database. The lattice constant in the crystal of nanocomposite increases with rising temperature in the reaction, leading to unit cell expansion, while increasing the stirring—rate leads to a random size distribution of the lattice parameter. Due to the imperfect growth of the crystal, the induced crystallite size was calculated using the Williamson-Hall model, and the precise lattice parameter values were calculated using the Nelson-Riley function. Full article
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Article
Growth and Passive Q-Switching Application of Cr:TiTe3O8 Crystal
Crystals 2022, 12(4), 558; https://doi.org/10.3390/cryst12040558 - 15 Apr 2022
Abstract
A Cr4+-doped TiTe3O8 crystal with dimensions up to 21 mm × 21 mm × 11 mm was grown successfully by the top-seeded solution growth method. A high-resolution X-ray diffraction experiment showed that the full width at half-maximum of [...] Read more.
A Cr4+-doped TiTe3O8 crystal with dimensions up to 21 mm × 21 mm × 11 mm was grown successfully by the top-seeded solution growth method. A high-resolution X-ray diffraction experiment showed that the full width at half-maximum of the rocking curve was 41.90″. Energy-dispersive spectrometry (EDS) and X-ray fluorescence spectroscopy (XRF) proved that Cr4+ ions have been doped into the TiTe3O8 crystal with molar percentage of 4.9%. The Cr:TiTe3O8 crystal exhibited an absorption range from 995 to 1565 nm, which is suitable for passive Q switch at 1064 nm. Then, a passive Q-switching solid-state laser operating at 1064 nm was realized using a Cr:TiTe3O8 crystal as the saturable absorber. The maximum laser pulse energy is calculated to be 0.7 μJ, and the maximum peak power reaches 0.7 W. Full article
(This article belongs to the Special Issue Feature Papers in Crystal Engineering in 2022)
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Article
On Stress-Induced Polarization Effect in Ammonothermally Grown GaN Crystals
Crystals 2022, 12(4), 554; https://doi.org/10.3390/cryst12040554 - 15 Apr 2022
Abstract
The results of basic ammonothermal crystallization of gallium nitride are described. The material is mainly analyzed in terms of the formation of stress (called stress-induced polarization effect) and defects (threading dislocations) appearing due to a stress relaxation process. Gallium nitride grown in different [...] Read more.
The results of basic ammonothermal crystallization of gallium nitride are described. The material is mainly analyzed in terms of the formation of stress (called stress-induced polarization effect) and defects (threading dislocations) appearing due to a stress relaxation process. Gallium nitride grown in different positions of the crystallization zone is examined in cross-polarized light. Interfaces between native ammonothermal seeds and new-grown gallium nitride layers are investigated in ultraviolet light. The etch pit densities in the seeds and the layers is determined and compared. Based on the obtained results a model of stress and defect formation is presented. New solutions for improving the structural quality of basic ammonothermal gallium nitride crystals are proposed. Full article
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Article
Resonance Analysis of Piezoelectric Bulk Acoustic Wave Devices Based on YCOB Crystals with Monoclinic Symmetry Excited by Lateral Electric Fields
Crystals 2022, 12(4), 542; https://doi.org/10.3390/cryst12040542 - 12 Apr 2022
Abstract
The monoclinic YCOB crystal still maintains good piezoelectric properties at 800 °C; thus, it has a good application prospect in high-temperature piezoelectric acoustic wave sensors. However, due to the lower symmetry compared crystals in trigonal and tetragonal systems, the exciting characteristics of piezoelectric [...] Read more.
The monoclinic YCOB crystal still maintains good piezoelectric properties at 800 °C; thus, it has a good application prospect in high-temperature piezoelectric acoustic wave sensors. However, due to the lower symmetry compared crystals in trigonal and tetragonal systems, the exciting characteristics of piezoelectric plates based on monoclinic YCOB crystals are more complicated. The vibration analysis model of lateral-field-excitation (LFE) devices based on monoclinic crystals is scarce; thus, the coupling relationships between different vibration modes and energy-trapping characteristics of the devices are unclear, which hinders the optimal design of devices. In this paper, by using Mindlin plate theory, the high-frequency vibrations of piezoelectric resonators based on monoclinic YCOB crystal plates excited by a lateral electric field are modeled and analyzed. The coupling relationships between the vibration modes of the device are clarified. The influences of the electrode width, electrode/plate mass ratio and electrode gap value on resonances and energy-trapping characteristics of the device are achieved. In addition, the effects of the structure parameters on the mass sensitivity of the monoclinic YCOB LFE devices are investigated, which are further verified by FEM simulations. The results are crucial to obtaining good resonance and sensing characteristics for LFE high-temperature piezoelectric sensors based on crystals with monoclinic symmetry. Full article
(This article belongs to the Special Issue Ferroelectrics)
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Article
Periodicity of Superatomic Hybrid Orbitals in Substituted Superatoms and Superatomic-like [email protected]12 (X = Li~Kr) Clusters
Crystals 2022, 12(4), 543; https://doi.org/10.3390/cryst12040543 - 12 Apr 2022
Abstract
A superatom is a cluster composed of a specific number of atoms. We recently found that the superatom-like [email protected]12 (X = Li~Kr) clusters has the periodic energy levels of the specific orbitals 2S and 2P by means of the DV-Xα molecular orbital [...] Read more.
A superatom is a cluster composed of a specific number of atoms. We recently found that the superatom-like [email protected]12 (X = Li~Kr) clusters has the periodic energy levels of the specific orbitals 2S and 2P by means of the DV-Xα molecular orbital calculation method. This periodicity in energy levels has not been seen in 1D or 1F orbitals. We supposed that the periodicity of the energy levels of the 2S and 2P superatomic-like orbitals come from the same symmetry between atomic orbitals as the central atom X and the surrounding specific orbitals, according to the Jellium model. Both the s and p atomic orbitals of the central atom X in the superatom-like [email protected]12 have a large shielding effect, suggesting that the s and p atomic orbitals interact strongly with both 2S and 2P superatomic-like orbitals. The energy level periodicity has the potential to periodically change the number of electrons located in the 1D and 1F orbitals, which is related to magnetic properties and is expected to be useful for novel magnetic devices by periodically controlling the magnetism of superatoms. Full article
(This article belongs to the Topic First-Principles Simulation—Nano-Theory)
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Article
Envelope Function Analysis of Quasicrystals
Crystals 2022, 12(4), 536; https://doi.org/10.3390/cryst12040536 - 11 Apr 2022
Abstract
Quasicrystals have attracted a growing interest in material science because of their unique properties and applications. Proper determination of the atomic structure is important in designing a useful application of these materials, for which a difficult phase problem of the structure factor must [...] Read more.
Quasicrystals have attracted a growing interest in material science because of their unique properties and applications. Proper determination of the atomic structure is important in designing a useful application of these materials, for which a difficult phase problem of the structure factor must be solved. Diffraction patterns of quasicrystals consist of a periodic series of peaks, which can be reduced to a single envelope. Knowing the distribution of the diffraction image into series, it is possible to recover information about the phase of the structure factor without using time-consuming iterative methods. By the inverse Fourier transform, the structure factor can be obtained (enclosed in the shape of the average unit cell, or atomic surface) directly from the diffraction patterns. The method based on envelope function analysis was discussed in detail for a model 1D (Fibonacci chain) and 2D (Penrose tiling) quasicrystal. First attempts to apply this technique to a real Al-Cu-Rh decagonal quasicrystal were also made. Full article
(This article belongs to the Special Issue Frontiers of Intermetallic Compounds)
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Article
Zeolitic Imidazolate Framework 67-Derived Ce-Doped [email protected] Carbon Hollow Polyhedron as High-Performance Anodes for Lithium-Ion Batteries
Crystals 2022, 12(4), 533; https://doi.org/10.3390/cryst12040533 - 11 Apr 2022
Abstract
Zeolitic Imidazolate Framework 67 (ZIF-67) and its derivates have attracted extensive interest for lithium-ion batteries (LIBs). Here, Cerium-doped cobalt [email protected] carbon (Ce-doped [email protected]) with hollow polyhedron structure materials were successfully synthesized via ionic-exchange with Co and Ce ions using the ZIF-67 as a [...] Read more.
Zeolitic Imidazolate Framework 67 (ZIF-67) and its derivates have attracted extensive interest for lithium-ion batteries (LIBs). Here, Cerium-doped cobalt [email protected] carbon (Ce-doped [email protected]) with hollow polyhedron structure materials were successfully synthesized via ionic-exchange with Co and Ce ions using the ZIF-67 as a template followed with a facile low-temperature phosphorization treatment. Benefitting from the well-designed hollow polyhedron, steady carbon network, and Ce-doping structural merits, the as-synthesized Ce-doped [email protected] electrode demonstrated superior performance as the anode in LIBs: a superior cyclability (400 mA h g−1 after 500 cycles) and outstanding rate-capability (590 mA h g−1, reverted to 100 mA g−1). These features not only produced more lithium-active sites for LIBs anode and a shorter Li-ion diffusion pathway to expedite the charge transfer, but also the better tolerance against volume variation of CoP during the repeated lithiation/delithiation process and greater electronic conductivity properties. These results provide a methodology for the design of well-organized ZIFs and rare earth element-doped transition metal phosphate with a hollow polyhedron structure. Full article
(This article belongs to the Special Issue Emerging Low-Dimensional Materials)
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Article
Fullerene in a Magnetic Field
Crystals 2022, 12(4), 521; https://doi.org/10.3390/cryst12040521 - 08 Apr 2022
Abstract
The manuscript presents a trajectory method for describing the rotations of surface crystals such as fullerenes, nanotubes, and nanotori. This method does not require the implementation of successive rotations of the considered molecular structures around the axes of the selected basis. Therefore, it [...] Read more.
The manuscript presents a trajectory method for describing the rotations of surface crystals such as fullerenes, nanotubes, and nanotori. This method does not require the implementation of successive rotations of the considered molecular structures around the axes of the selected basis. Therefore, it is free from the shortcomings of the approaches of Euler and Hamilton. On its basis, an efficient algorithm for calculating the motions of a magneto-susceptible fullerene in an alternating magnetic field has been developed. The nature of rotation of fullerenes in fields of various configurations has been studied. Full article
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Article
Properties of Sm-Doped SrCl2 Crystalline Scintillators
Crystals 2022, 12(4), 517; https://doi.org/10.3390/cryst12040517 - 08 Apr 2022
Abstract
Sm-doped SrCl2 crystals were prepared, and the scintillation properties such as emission spectra, decay profiles, and pulse height were investigated. Under X-ray irradiation, a broad band can be observed at 680 nm, which indicates that the major origin is due to 5d-4f [...] Read more.
Sm-doped SrCl2 crystals were prepared, and the scintillation properties such as emission spectra, decay profiles, and pulse height were investigated. Under X-ray irradiation, a broad band can be observed at 680 nm, which indicates that the major origin is due to 5d-4f transitions of Sm2+. The decay curve is approximated by one exponential function with a decay time of 10 μs, and the decay time constant is typical for Sm2+. From the pulse height of 137Cs γ-rays, 0.1% Sm:SrCl2 shows a light yield of 33,000 photons/MeV. Full article
(This article belongs to the Section Inorganic Crystalline Materials)
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Article
Effect of Non-Covalent Interactions on the 2,4- and 3,5-Dinitrobenzoate Eu-Cd Complex Structures
Crystals 2022, 12(4), 508; https://doi.org/10.3390/cryst12040508 - 06 Apr 2022
Abstract
Heterometallic {Eu2Cd2} complexes [Eu2(NO3)2Cd2(Phen)2(2,4-Nbz)8]n·2nMeCN (I) and [Eu2(MeCN)2Cd2(Phen)2(3,5-Nbz)10] (II) with the 2,4-dinitrobenzoate (2,4-Nbz) and [...] Read more.
Heterometallic {Eu2Cd2} complexes [Eu2(NO3)2Cd2(Phen)2(2,4-Nbz)8]n·2nMeCN (I) and [Eu2(MeCN)2Cd2(Phen)2(3,5-Nbz)10] (II) with the 2,4-dinitrobenzoate (2,4-Nbz) and 3,5-dinitrobenzoate (3,5-Nbz) anions and 1,10-phenanthroline were synthesized. The compounds obtained were characterized by X-ray single-crystal analysis, powder X-ray diffraction analysis, IR spectroscopy, and elemental analysis. Moreover, the thermal stability of the complexes was also studied. Analysis of the crystal packing showed that where 1,10-phenanthroline is combined with various isomers of dinitrobenzoate anions, different arrangements of non-covalent interactions are observed in the complex structures. In the case of the compound with the 2,4-dinitrobenzoate anion, these interactions lead to a significant distortion of the metal core geometry and formation of a polymeric structure, while the complex with the 3,5-dinitrobenzoate anion has a structure that is typical of similar systems. The absence of europium metal-centered luminescence at 270 nm wavelength was shown. For all the reported compounds, a thermal stability study was carried out that showed that the compounds decomposed with a significant thermal effect. Full article
(This article belongs to the Special Issue Feature Papers in Organic Crystalline Materials)
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Article
Crystalline State Hydrogen Bonding of 2-(2-Hydroxybenzylidene)Thiazolo[3,2-a]Pyrimidines: A Way to Non-Centrosymmetric Crystals
Crystals 2022, 12(4), 494; https://doi.org/10.3390/cryst12040494 - 02 Apr 2022
Abstract
Thiazolopyrimidines are attractive to medical chemists as new antitumor agents due to their high inhibiting activity towards the tumor cells replication process and easy modification of their structure by varying of the number and nature of substituents. The presence of asymmetric C5 carbon [...] Read more.
Thiazolopyrimidines are attractive to medical chemists as new antitumor agents due to their high inhibiting activity towards the tumor cells replication process and easy modification of their structure by varying of the number and nature of substituents. The presence of asymmetric C5 carbon atoms requires the development of racemic mixture separation procedures for these heterocycles. One of the more effective ways is the crystallization of a racemic compound as a conglomerate. A prerequisite for such separation is the formation of non-centrosymmetric crystals presenting Sohncke space groups. For the construction of chiral supramolecular ensembles in a crystalline state, hydrogen bonds were chosen as supramolecular synthons. In this context, salicylic derivatives at the C2 atom of thiazolopyrimidines were synthesized. The crystal structures of the obtained compounds were established by SCXRD. The regularities of the solvent’s influence on the crystal packaging were revealed. The conditions for the preparation of crystals with the chiral space group due to intermolecular hydrogen bonds were discovered. Full article
(This article belongs to the Special Issue Advances in Chiral Crystallization, Resolution and Deracemization)
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Article
Phase Transitions and Amorphization of M2AgF4 (M = Na, K, Rb) Compounds at High Pressure
Crystals 2022, 12(4), 458; https://doi.org/10.3390/cryst12040458 - 25 Mar 2022
Abstract
We report the results of high-pressure Raman spectroscopy studies of alkali metal fluoroargentates (M2AgF4, where M = Na, K, Rb) combined with theoretical and X-ray diffraction studies for the K member of the series. Theoretical density functional calculations predict [...] Read more.
We report the results of high-pressure Raman spectroscopy studies of alkali metal fluoroargentates (M2AgF4, where M = Na, K, Rb) combined with theoretical and X-ray diffraction studies for the K member of the series. Theoretical density functional calculations predict two structural phase transitions for K2AgF4: one from low-pressure monoclinic P21/c (beta) phase to intermediate-pressure tetragonal I42d structure at 6 GPa, and another to high-pressure triclinic P1 phase at 58 GPa. However, Raman spectroscopy and X-ray diffraction data indicate that both polymorphic forms of K2AgF4, as well as two other fluoroargentate phases studied here, undergo amorphization at pressures as low as several GPa. Full article
(This article belongs to the Special Issue Advances in Halide Perovskite Materials)
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Article
Scintillation Properties of Pr-Doped Lanthanum Pyrosilicate Single Crystals
Crystals 2022, 12(4), 459; https://doi.org/10.3390/cryst12040459 - 25 Mar 2022
Abstract
Five samples of lanthanum pyrosilicate (La2Si2O7) single crystals with 0.5–10.0% Praseodymium (Pr)-doping concentrations were synthesized by the floating-zone method. Photoluminescence and scintillation properties of these crystals were investigated in this study for the first time. The multiple [...] Read more.
Five samples of lanthanum pyrosilicate (La2Si2O7) single crystals with 0.5–10.0% Praseodymium (Pr)-doping concentrations were synthesized by the floating-zone method. Photoluminescence and scintillation properties of these crystals were investigated in this study for the first time. The multiple emissions from electron transitions of Pr3+ were observed on both a photoluminescence emission map and scintillation spectra, including the desired emission band of Pr3+ 5d–4f transition at 250–310 nm. The major photoluminescence and scintillation decay times were approximately 19 and 26 ns, respectively. When compared with commercial scintillators such as Tl-doped cesium iodide (CsI), the Pr-doped La2Si2O7 samples presented a respectively low afterglow level of 32 ppm after 20 ms of X-ray irradiation. Under 662 keV γ-ray irradiation from 137Cs, the 3.0% Pr-doped La2Si2O7 sample presented a scintillation light yield of 3200 ph/MeV, which was the best value among the tested samples. Full article
(This article belongs to the Special Issue Optoelectronics and Photonics in Crystals)
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Article
Second-Order Raman Scattering in Ferroelectric Ceramic Solid Solutions LiNbxTa1−xO3
Crystals 2022, 12(4), 456; https://doi.org/10.3390/cryst12040456 - 24 Mar 2022
Abstract
In the second-order Raman spectra of ceramic solid solutions, LiNbxTa1−xO3 weak overtone bands of fully symmetric fundamental polar excitations were observed for the first time. The frequencies of the two bands exceeded the value of the overtone frequency [...] Read more.
In the second-order Raman spectra of ceramic solid solutions, LiNbxTa1−xO3 weak overtone bands of fully symmetric fundamental polar excitations were observed for the first time. The frequencies of the two bands exceeded the value of the overtone frequency corresponding to the fully symmetrical vibration 4A1(z). The possibility of the existence of phonon bound states of the antipolar type in the vibrational spectrum of LiNbxTa1−xO3 ceramics is predicted. Full article
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Article
Phase Diagram of a Strained Ferroelectric Nanowire
Crystals 2022, 12(4), 453; https://doi.org/10.3390/cryst12040453 - 24 Mar 2022
Abstract
Ferroelectric materials manifest unique dielectric, ferroelastic, and piezoelectric properties. A targeted design of ferroelectrics at the nanoscale is not only of fundamental appeal but holds the highest potential for applications. Compared to two-dimensional nanostructures such as thin films and superlattices, one-dimensional ferroelectric nanowires [...] Read more.
Ferroelectric materials manifest unique dielectric, ferroelastic, and piezoelectric properties. A targeted design of ferroelectrics at the nanoscale is not only of fundamental appeal but holds the highest potential for applications. Compared to two-dimensional nanostructures such as thin films and superlattices, one-dimensional ferroelectric nanowires are investigated to a much lesser extent. Here, we reveal a variety of the topological polarization states, particularly the vortex and helical chiral phases, in loaded ferroelectric nanowires, which enable us to complete the strain–temperature phase diagram of the one-dimensional ferroelectrics. These phases are of prime importance for optoelectronics and quantum communication technologies. Full article
(This article belongs to the Special Issue Research and Development of Ferroelectric Material)
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Article
Molecular Self-Assembly of an Unusual Dinuclear Ruthenium(III) Complex Based on the Nucleobase Guanine
Crystals 2022, 12(4), 448; https://doi.org/10.3390/cryst12040448 - 23 Mar 2022
Abstract
The study of crystal structures based on complexes containing purine nucleobases is a significant research subject, mainly regarding the diagnosis and treatment of some diseases and the investigation of genetic mutations and biochemical structures in life sciences. We have obtained and characterized a [...] Read more.
The study of crystal structures based on complexes containing purine nucleobases is a significant research subject, mainly regarding the diagnosis and treatment of some diseases and the investigation of genetic mutations and biochemical structures in life sciences. We have obtained and characterized a new dinuclear ruthenium(III) complex based on guanine with the formula [{Ru(µ-Cl)(µ-gua)}2Cl4]·2H2O (1) (gua = guanine). 1 was characterized by means of Fourier transform infrared spectroscopy (FT–IR), scanning electron microscopy and energy dispersive X-ray analysis (SEM–EDX), single-crystal X-ray diffraction (XRD), Hirshfeld surface analysis and cyclic voltammetry (CV). The study of its electrochemical properties allowed us to investigate the presence of guanine molecules when linked to the ruthenium(III) ion in 1. The well-resolved voltammetric response together with the reliability and stability achieved through 1 could provide a step forward to developing new ruthenium-based platforms, devices and modified electrodes adequate to study this purine nucleobase. Full article
(This article belongs to the Special Issue Self-Assembled Complexes: “Love at First Sight”)
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Article
Synthesis and Structural Characterization of a New 1,2,3-Triazole Derivative of Pentacyclic Triterpene
Crystals 2022, 12(3), 422; https://doi.org/10.3390/cryst12030422 - 18 Mar 2022
Abstract
The new 30-substituted triazole derivative of 3,28-O,O′-diacetylbetulin was obtained in the copper(I) catalyzed azide-alkyne cycloaddition (CuAAC). The title compound was characterized by NMR, IR, HR-MS, and X-ray diffraction techniques. The X-ray diffraction study showed that the 1,2,3-triazole derivative crystallizes [...] Read more.
The new 30-substituted triazole derivative of 3,28-O,O′-diacetylbetulin was obtained in the copper(I) catalyzed azide-alkyne cycloaddition (CuAAC). The title compound was characterized by NMR, IR, HR-MS, and X-ray diffraction techniques. The X-ray diffraction study showed that the 1,2,3-triazole derivative crystallizes in the orthorhombic space group P212121, Z = 4, and unit cell parameters are as follows a = 9.4860(10) Å, b = 13.9440(2) Å, and c = 30.2347(4) Å. The molecular packing is stabilized by intermolecular hydrogen interactions C-H…O. The Hirshfeld surface analysis showed the presence of the O…H interactions with a percentage of the 16.5% in the total Hirshfeld area. The MEP analysis showed that the nucleophilic regions are located near the oxygen atoms of the acyl and carbonyl groups of betulin moiety and the sulfur atom in the triazole linker. The HOMO and LUMO orbitals are located near the triazole moiety. The obtained results indicated that this new betulin derivative is more reactive with electrophilic than nucleophilic molecules. Full article
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Article
Scalable and Blue Photoluminescence Emissions of (C4H9NH3)2PbBr4 2D Perovskite Fabricated by the Dip-Coating Method Using a Co-Solvent System
Crystals 2022, 12(3), 418; https://doi.org/10.3390/cryst12030418 - 18 Mar 2022
Abstract
The improved efficiency of perovskite-related photovoltaic devices, such as light-emitting diodes (LEDs), is related to film uniformity, the compactness of each layer, and thickness. Herein, we improved the traditional single-solvent, solution-processed method and developed a co-solvent method to prepare a two-dimensional (2D) (C [...] Read more.
The improved efficiency of perovskite-related photovoltaic devices, such as light-emitting diodes (LEDs), is related to film uniformity, the compactness of each layer, and thickness. Herein, we improved the traditional single-solvent, solution-processed method and developed a co-solvent method to prepare a two-dimensional (2D) (C4H9NH3)2PbBr4 perovskite film for blue photoluminescence (PL) emissions. A poor film-forming uniformity was observed for the use of the single-solvent, dimethylformamide (DMF) method. In adding 1,2-dichlorobenzene (ODCB) of a smaller polarity to DMF, the co-solvent engineering dramatically changed the film-forming properties. Optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffractometer (XRD), and time-resolved PL (TR-PL) spectroscopy analyses confirmed that the perovskite film prepared by the co-solvent system had a good crystallinity, fewer defects, and a longer carrier lifetime. These experimental results show a simple, scalable (1.23 × 1.23 cm2), and stable reproducibility method for preparing 2D perovskite of 415 nm wavelength PL emissions that might be beneficial for the development of ultraviolet (UV) photodetectors, blue LEDs, and high-resolution displays. Full article
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Article
Compressive Mechanics and Hyperelasticity of Ni-Ti Lattice Structures Fabricated by Selective Laser Melting
Crystals 2022, 12(3), 408; https://doi.org/10.3390/cryst12030408 - 17 Mar 2022
Abstract
Additively manufactured Ni-Ti lattice structures have controllable bio/mechanical properties, as well as excellent large deformation and damping properties similar to those of natural bone. They have broad application prospects in the field of bone implantation. Triply Periodic Minimal Surface (TPMS) structures are believed [...] Read more.
Additively manufactured Ni-Ti lattice structures have controllable bio/mechanical properties, as well as excellent large deformation and damping properties similar to those of natural bone. They have broad application prospects in the field of bone implantation. Triply Periodic Minimal Surface (TPMS) structures are believed to be the most potential and ideal bionic bone structures. In this work, Ni-Ti Gyroid-type TPMS lattice structures were fabricated by selective laser melting (SLM) and their manufacturing fidelity and compression properties were evaluated. By changing the maximum strain value, the hyperelastic recovery performance under cyclic stress was investigated. The results showed that the Ni-Ti Gyroid lattice structures fabricated by SLM had excellent manufacturability (relative density can reach 98.93%) and mechanical properties (elastic modulus is about 130.8 MPa, ultimate strength is about 2.7 MPa). The hyperelastic cycle testing showed that the elastic modulus, yield strength and ultimate strength of the lattice structures tended to stablilize gradually with increasing numbers of cycles. The residual strain increased with the number of cycles, and as the maximum strain increased from 4% to 8%, the residual strain also increased from 1% to 4%. Full article
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Article
Influence of Solidification Parameters on the Amount of Eutectic and Secondary Arm Spacing of Al–7wt% Si Alloy Solidified under Microgravity
Crystals 2022, 12(3), 414; https://doi.org/10.3390/cryst12030414 - 17 Mar 2022
Abstract
During the solidification of hypoeutectic Al–7% Si alloy, density differences develop in the melt due to variations in concentration and temperature. On Earth, melt flow can occur due to gravity, which then affects the solidification process. The microgravity environment strongly eliminates convection in [...] Read more.
During the solidification of hypoeutectic Al–7% Si alloy, density differences develop in the melt due to variations in concentration and temperature. On Earth, melt flow can occur due to gravity, which then affects the solidification process. The microgravity environment strongly eliminates convection in the melt and allows investigation of the solidification process in purely diffusive circumstances. In this study, four solidification experiments were performed on grain-refined and non-grain-refined Al–7 wt% Si alloy on-board the International Space Station (ISS) in the Materials Science Lab (MSL) to study the effect of solidification parameters (solid/liquid front velocity (v) and temperature gradient (G)) on the grain structure and dendritic microstructure. The grain structure has been analyzed in detail in some earlier studies. The aim of this work was to carry out detailed analysis of the macrosegregation caused by the diffusion of Si from the initial mushy zone during the homogenization step and the subsequent solidification phase of the experiments as well as the correlated distribution of eutectic along the solidification direction. The secondary dendrite arm spacing (SDAS) for different process conditions was also studied. For these two issues, microgravity experimental results were compared to simulation results. The macrosegregation was calculated by the finite difference method. Because the steady-state solidification conditions were never reached, the solidification process was characterized by the average front velocity and temperature gradient. Considering the actual liquidus temperature (TL) caused by macrosegregation, the SDAS was calculated as a function of the average processing parameters and the actual liquidus temperature with the classical Kirkwood’s equation. As a result, good agreement was obtained between the calculated and measured SDAS. Full article
(This article belongs to the Special Issue Microstructure Characterization and Design of Alloys)
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Article
Influence of Surface Relief on Orientation of Nematic Liquid Crystals: Polyimide Doped with WS2 Nanotubes
Crystals 2022, 12(3), 391; https://doi.org/10.3390/cryst12030391 - 14 Mar 2022
Abstract
Among the different methods for orienting liquid crystal (LC) molecules, adding nanoparticles into the matrix of the substrate material towards modifying its surface, is actively pursued. In this context, the influence of the nanoparticle content on the texture of the surface of polymer [...] Read more.
Among the different methods for orienting liquid crystal (LC) molecules, adding nanoparticles into the matrix of the substrate material towards modifying its surface, is actively pursued. In this context, the influence of the nanoparticle content on the texture of the surface of polymer film used as the substrate for the LC orientation is of particular interest. Thus, in the current paper, WS2 nanotubes were used to dope the polyimide (PI) substrate-film in order to modify and control its surface morphology/roughness and properties. The modified organic surface structure is applied in order to achieve a new means for controlling the orientation of the LC molecules. This tool adds to the classical methods for controlling the orientation of the LC molecules, such as the display technique. Full article
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Article
An Investigation of the Pressure-Induced Structural Phase Transition of Nanocrystalline α-CuMoO4
Crystals 2022, 12(3), 365; https://doi.org/10.3390/cryst12030365 - 09 Mar 2022
Cited by 1
Abstract
The structural behavior of nanocrystalline α-CuMoO4 was studied at ambient temperature up to 2 GPa using in situ synchrotron X-ray powder diffraction. We found that nanocrystalline α-CuMoO4 undergoes a structural phase transition into γ-CuMoO4 at 0.5 GPa. The structural sequence [...] Read more.
The structural behavior of nanocrystalline α-CuMoO4 was studied at ambient temperature up to 2 GPa using in situ synchrotron X-ray powder diffraction. We found that nanocrystalline α-CuMoO4 undergoes a structural phase transition into γ-CuMoO4 at 0.5 GPa. The structural sequence is analogous to the behavior of its bulk counterpart, but the transition pressure is doubled. A coexistence of both phases was observed till 1.2 GPa. The phase transition gives rise to a change in the copper coordination from square-pyramidal to octahedral coordination. The transition involves a volume reduction of 13% indicating a first-order nature of the phase transition. This transformation was observed to be irreversible in nature. The pressure dependence of the unit-cell parameters was obtained and is discussed, and the compressibility analyzed. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Volume II))
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Article
The Growth of Hexagonal Boron Nitride Quantum Dots on Polycrystalline Nickel Films by Plasma-Assisted Molecular Beam Epitaxy
Crystals 2022, 12(3), 347; https://doi.org/10.3390/cryst12030347 - 03 Mar 2022
Abstract
In this report, quantum dots of hexagonal boron nitride (h-BN) were fabricated on the surface of polycrystalline Ni film at low growth temperatures (700, 750, and 800 °C) by plasma-assisted molecular beam epitaxy. Reflection high-energy electron diffraction could trace the surface condition during [...] Read more.
In this report, quantum dots of hexagonal boron nitride (h-BN) were fabricated on the surface of polycrystalline Ni film at low growth temperatures (700, 750, and 800 °C) by plasma-assisted molecular beam epitaxy. Reflection high-energy electron diffraction could trace the surface condition during the growth and perform the formation of BN. The observation of surface morphology by scanning electron microscopy and atomic force microscopy showed the nanodots of BN on Ni films. The existence of crystal h-BN quantum dots was determined by the analysis of Raman spectra and Kevin probe force microscopy. The cathodoluminescence of h-BN quantum dots performed at the wavelength of 546 and 610 nm, attributed to the trapping centers involving impurities and vacancies. Moreover, the influence of temperatures for the substrate and boron source cell was also investigated in the report. When the k-cell temperature of boron and growth temperature of substrate increased, the emission intensity of cathodoluminescence spectra increased, indicating the better growth parameters for h-BN quantum dots. Full article
(This article belongs to the Special Issue Confined Crystals, Quantum Dots, and Nano Crystals)
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Article
Unusual Lattice Parameters Behavior for La1.9Ca0.1NiO4+δ at the Temperatures below Oxygen Loss
Crystals 2022, 12(3), 344; https://doi.org/10.3390/cryst12030344 - 02 Mar 2022
Abstract
In this work, we studied the structural features of La1.9Ca0.1NiO4.11, which is considered a promising cathode material for intermediate temperature solid-oxide fuel cells (IT-SOFC). The effect of different pretreatments on the structural characteristics of the sample was [...] Read more.
In this work, we studied the structural features of La1.9Ca0.1NiO4.11, which is considered a promising cathode material for intermediate temperature solid-oxide fuel cells (IT-SOFC). The effect of different pretreatments on the structural characteristics of the sample was studied using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) in order to elucidate the origin of a peculiar change of lattice parameters observed earlier during in situ XRD studies. The XRD studies have shown that anisotropic broadening for reflections with a high Miller index l appears after tempering of a quenched (from 1100 °C) sample at 250 °C. This temperature is too low for the release/incorporation of oxygen into the structure but is sufficient for oxygen migration inside the structure. The HRTEM assisted us in revealing differences in the defect structure after different pretreatments. Based on obtained results, the following possible explanation was proposed. Observed additional microstrains and non-oriented planar defects as well as a decrease in the coherent scattering region size in the [00l] direction are caused by the non-homogeneous redistribution of interstitial oxygen in the structure during tempering. Full article
(This article belongs to the Special Issue Structure and Kinetics Modeling of Metal and Oxide Catalysts)
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Article
Theoretical Model for a Novel Electronic State in a Dirac Electron System Close to Merging: An Imaginary Element between Sulphur and Selenium
Crystals 2022, 12(3), 346; https://doi.org/10.3390/cryst12030346 - 02 Mar 2022
Cited by 2
Abstract
Topological materials with Dirac electron systems have been extensively studied. Organic crystalline materials form a unique group of such compounds with well-defined crystal structures. While most organic compounds require high pressures to exhibit Dirac-cone-type band structures, the title compound, α-STF2I3 [...] Read more.
Topological materials with Dirac electron systems have been extensively studied. Organic crystalline materials form a unique group of such compounds with well-defined crystal structures. While most organic compounds require high pressures to exhibit Dirac-cone-type band structures, the title compound, α-STF2I3, has garnered increasing interest due to its Dirac-cone-type band structure under ambient pressure. Various experiments have been conducted under ambient pressure; their results can be compared with those of theoretical calculations to obtain insights into Dirac electron systems. However, structural disorder peculiar to the STF molecules in the solid-state has prevented any type of theoretical calculation of the states. In this study, we report a new method for calculating intermolecular interactions in disordered systems based on the extended Hückel approximation. This method enables band calculations, suggesting that this material is a rare example of a system close to merging. The obtained band structure indicates that the characteristic disorder in the STF solids distributed electrons equally on the sulphur and selenium atoms as if they belong to an imaginary element between sulphur and selenium and are arranged without disorder. Full article
(This article belongs to the Special Issue Organic Conductors)
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Communication
Investigation of Lattice Plasmon Modes in 2D Arrays of Au Nanoantennas
Crystals 2022, 12(3), 336; https://doi.org/10.3390/cryst12030336 - 28 Feb 2022
Abstract
The coupling of gold nanoantennas (AuNAs) in the arrangement of monomers in bidimensional gratings is investigated both experimentally and numerically. The influence of edge diffraction, corresponding to the grazing propagation of specific diffracted orders, and the dependence of grating parameters on lattice plasmon [...] Read more.
The coupling of gold nanoantennas (AuNAs) in the arrangement of monomers in bidimensional gratings is investigated both experimentally and numerically. The influence of edge diffraction, corresponding to the grazing propagation of specific diffracted orders, and the dependence of grating parameters on lattice plasmon modes are studied. It is shown that the grating pitch influences the spectral position of the Rayleigh wavelength related to the grazing diffraction in air and/or in glass. In order to investigate the effect of diffraction and its interplay with the Rayleigh wavelength, extinction measurements with different incidence angles are carried out. For incidence angles above θ=20, along with the excitation of quadrupolar and vertical modes, very narrow dips or sharp excitations are observed in the spectra. These ones strongly depend on the respective spectral position of Rayleigh anomaly and specific dipolar mode, on the propagation direction of the grazing diffraction, and on the considered plasmon mode. These features are explained in the light of numerical calculations obtained with Green’s tensor method. All the above different characteristics and couplings are of great practical interest, especially for a possible implementation in biosensor devices and for other technological applications spanning from precision medicine and life science to telecommunications and energy systems. Full article
(This article belongs to the Special Issue Active Hybrid Soft Metamaterials)
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Article
Ice Dendrite Growth Atop a Frozen Drop under Natural Convection Conditions
Crystals 2022, 12(3), 323; https://doi.org/10.3390/cryst12030323 - 25 Feb 2022
Abstract
Condensation frosting is a type of icing encountered ubiquitously in our daily lives. Understanding the dynamics of condensation frosting is essential in developing effective technologies to suppress frost accretions that compromise heat transfer and system integrity. Here, we present an experimental study on [...] Read more.
Condensation frosting is a type of icing encountered ubiquitously in our daily lives. Understanding the dynamics of condensation frosting is essential in developing effective technologies to suppress frost accretions that compromise heat transfer and system integrity. Here, we present an experimental study on ice dendrite growth atop a single frozen drop, an important step affecting the subsequent frosting process, and the properties of fully-developed frost layers. We evaluate the effect of natural convection by comparing the growth dynamics of ice dendrites on the surface of a frozen drop with three different orientations with respect to gravity. The results show that both the average deposition rate and its spatial variations are profoundly altered by surface orientations. Such behavior is confirmed by a numerical simulation, showing how gravity-assisted (hindered) vapor diffusion yields the deposition outcomes. These findings benefit the optimization of anti-/de- frosting technologies and the rational design of heat exchangers. Full article
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Communication
Spinel LiMn2O4 Cathode Materials in Wide Voltage Window: Single-Crystalline versus Polycrystalline
Crystals 2022, 12(3), 317; https://doi.org/10.3390/cryst12030317 - 24 Feb 2022
Abstract
Single-crystal (SC) layered oxides as cathodes for Li-ion batteries have demonstrated better cycle stability than their polycrystalline (PC) counterparts due to the restrained intergranular cracking formation. However, there are rare reports on comparisons between single-crystal LiMn2O4 (SC-LMO) and polycrystalline LiMn [...] Read more.
Single-crystal (SC) layered oxides as cathodes for Li-ion batteries have demonstrated better cycle stability than their polycrystalline (PC) counterparts due to the restrained intergranular cracking formation. However, there are rare reports on comparisons between single-crystal LiMn2O4 (SC-LMO) and polycrystalline LiMn2O4 (PC-LMO) spinel cathodes for Li-ion storage. In this work, the Li-ion storage properties of spinel LiMn2O4 single-crystalline and polycrystalline with similar particle sizes were investigated in a wide voltage window of 2–4.8 V vs. Li/Li+. The SC-LMO cathode exhibited a specific discharge capacity of 178 mA·h·g−1, which was a bit larger than that of the PC-LMO cathode. This is mainly because the SC-LMO cathode showed much higher specific capacity in the 3 V region (Li-ion storage at octahedral sites with cubic to tetragonal phase transition) than the PC-LMO cathode. However, unlike layered-oxide cathodes, the PC-LMO cathode displayed better cycle stability than the SC-LMO cathode. Our studies for the first time demonstrate that the phase transition-induced Mn(II) ion dissolution in the 3 V region rather than cracking formation is the limiting factor for the cycle performance of spinel LiMn2O4 in the wide voltage window. Full article
(This article belongs to the Special Issue Supercapacitors with High Energy Density)
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Article
Compositions of Gamma and Gamma Prime Phases in an As-Cast Nickel-Based Single Crystal Superalloy Turbine Blade
Crystals 2022, 12(2), 299; https://doi.org/10.3390/cryst12020299 - 20 Feb 2022
Cited by 1
Abstract
The core and the interdendritic regions of an as-cast nickel based single crystal turbine blade were observed by electron microscopy to understand the microstructural development during an investment casting process. The dendrite core region shows an irregular morphology of gamma prime in gamma [...] Read more.
The core and the interdendritic regions of an as-cast nickel based single crystal turbine blade were observed by electron microscopy to understand the microstructural development during an investment casting process. The dendrite core region shows an irregular morphology of gamma prime in gamma due to a relatively short casting time, which prevented the development of gamma prime expected in a solution heat-treated microstructure. By comparison, the interdendritic region comprises three different regions composed of: several elongated gamma prime particles, relatively tiny and irregular gamma prime, and gamma prime with relatively regular morphology. The chemical analysis of these phases showed that, regardless of the analysis point in the core or the interdendritic region, almost the same compositions were acquired in the regular type of gamma and gamma prime phases. This result suggests that if the gamma prime forms in the gamma matrix, the composition of gamma prime is almost uniform regardless of the region and prevailing general chemical composition. In contrast, the composition of the elongated gamma prime in the interdendritic region was slightly different depending on the analysis point even within the same elongated particle. Full article
(This article belongs to the Topic Single-Crystal Ni-Based Alloys)
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Communication
Intermolecular Interactions Drive the Unusual Co-Crystallization of Different Calix[4]arene Conformations
Crystals 2022, 12(2), 250; https://doi.org/10.3390/cryst12020250 - 12 Feb 2022
Abstract
Crystallization of 5,17-dibromo-11,27,23,25-tetraone-26,28-dipropoxycalix[4]arene results in the rare observation of two different calix[4]arene conformations (partial cone and 1,3-alternate) co-crystallized within the same single crystal X-ray structure. Analysis using 1H and 13C NMR spectroscopy revealed that only a single conformation (the cone) was [...] Read more.
Crystallization of 5,17-dibromo-11,27,23,25-tetraone-26,28-dipropoxycalix[4]arene results in the rare observation of two different calix[4]arene conformations (partial cone and 1,3-alternate) co-crystallized within the same single crystal X-ray structure. Analysis using 1H and 13C NMR spectroscopy revealed that only a single conformation (the cone) was present in solution, and in contrast to the structures of other reported calix[4]arenes and calix[4]quinones, both conformations of the compound present in this crystal structure have a “pinched” shape, drastically reducing Br-Br separation and associated cavity sizes. Full article
(This article belongs to the Special Issue Advances in Functional Cocrystals)
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Article
Effects of Electron Correlation inside Disordered Crystals
Crystals 2022, 12(2), 237; https://doi.org/10.3390/cryst12020237 - 09 Feb 2022
Abstract
We propose a novel approach for characterising the electron spectrum of disordered crystals constructed from a Hamiltonian of electrons as well as phonons and a diagram approach for Green’s function. The system’s electronic states were modelled by means of the multi-band, tight-binding approach. [...] Read more.
We propose a novel approach for characterising the electron spectrum of disordered crystals constructed from a Hamiltonian of electrons as well as phonons and a diagram approach for Green’s function. The system’s electronic states were modelled by means of the multi-band, tight-binding approach. The system’s Hamiltonian is described based on the electron wave functions at the field of the atom nucleus. Our novel approach incorporates the long-range Coulomb interplay of electrons located in different lattice positions. Explicit interpretations of Green’s functions are derived using a diagram method. Equations are obtained for the vertex components for the mass operators of the electron–electron as well aselectron–phonon interplays. A system of equations for the spectrum of elementary excitations in the crystal is obtained, in which the vertex components for the mass operators of electron–electron as well as electron–phonon interplays are renormalised. Thismakes it possible to perform numerical computationsfor the system’s energy spectrum with a predetermined accuracy. In contrast to other approaches in which electron correlations are only taken into account in the limiting cases of an infinitely large and infinitesimal electron density, in this method, electron correlations are described in the general case of an arbitrary density. We obtained the cluster expansion of the density of states (DOS) of the disordered systems. We demonstrate that the addition of the electron-scattering mechanismsto the clusters is decreasing. This happens due to a growing number of positions in the cluster, which hang ontothe small parameter. The computing exactness is fixed by a small parameter for cluster expansion of Green’s functions of electrons as well as phonons. Full article
(This article belongs to the Special Issue Diffusion and Degradation Phenomena in Solid Oxide Materials)
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