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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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14 pages, 10069 KiB  
Article
Crystalline Microstructure, Microsegregations, and Mechanical Properties of Inconel 718 Alloy Samples Processed in Electromagnetic Levitation Facility
by Yindong Fang, Chu Yu, Nikolai Kropotin, Martin Seyring, Katharina Freiberg, Matthias Kolbe, Stephanie Lippmann and Peter K. Galenko
Crystals 2024, 14(3), 244; https://doi.org/10.3390/cryst14030244 - 29 Feb 2024
Cited by 2 | Viewed by 1539
Abstract
The solidification of Inconel 718 alloy (IN718) from undercooled liquid is studied. The solidification kinetics is evaluated in melted and undercooled droplets processed using the electromagnetic levitation (EML) technique by the temperature–time profiles and solid/liquid (S/L) interface movement during recalescence. The kinetics is [...] Read more.
The solidification of Inconel 718 alloy (IN718) from undercooled liquid is studied. The solidification kinetics is evaluated in melted and undercooled droplets processed using the electromagnetic levitation (EML) technique by the temperature–time profiles and solid/liquid (S/L) interface movement during recalescence. The kinetics is monitored in real time by special pyrometrical measurements and high-speed digital camera. It is shown that the growth velocity of γ-phase (the primary phase in IN718), the final crystalline microstructure (dendritic and grained), and the mechanical properties (microhardness) are strongly dependent on the initial undercooling ΔT at which the samples started to solidify with the originating γ-phase. Particularly, with the increase in undercooling, the secondary dendrite arm spacing decreases from 28 μm to 5 μm. At small and intermediate ranges of undercooling, the solidified droplets have a dendritic crystalline microstructure. At higher undercooling values reached in the experiment, ΔT>160 K (namely, for samples solidified with ΔT=170 K and ΔT=263 K), fine crystalline grains are observed instead of the dendritic structure of solidified drops. Such change in the crystalline morphology is qualitatively consistent with the behavior of crystal growth kinetics which exhibits the change from the power law to linear law at ΔT≈160 K in the velocity–undercooling relationship (measured by the advancement of the recalescence front in solidifying droplets). Study of the local mechanical properties shows that the microhardness increases with the increase in the γ″-phase within interdendritic spacing. The obtained data are the basis for testing the theoretical and computational of multicomponent alloy samples. Full article
(This article belongs to the Special Issue Phase Transition in External Fields (2nd Edition))
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14 pages, 4766 KiB  
Article
Investigation into the Effects of Cross-Sectional Shape and Size on the Light-Extraction Efficiency of GaN-Based Blue Nanorod Light-Emitting Diode Structures
by Bohae Lee and Han-Youl Ryu
Crystals 2024, 14(3), 241; https://doi.org/10.3390/cryst14030241 - 29 Feb 2024
Cited by 2 | Viewed by 1806
Abstract
We investigated the effect of cross-sectional shape and size on the light-extraction efficiency (LEE) of GaN-based blue nanorod light-emitting diode (LED) structures using numerical simulations based on finite-difference time-domain methods. For accurate determination, the LEE and far-field pattern (FFP) were evaluated by averaging [...] Read more.
We investigated the effect of cross-sectional shape and size on the light-extraction efficiency (LEE) of GaN-based blue nanorod light-emitting diode (LED) structures using numerical simulations based on finite-difference time-domain methods. For accurate determination, the LEE and far-field pattern (FFP) were evaluated by averaging them over emission spectra, polarization, and source positions inside the nanorod. The LEE decreased as rod size increased, owing to the nanorods’ increased ratio of cross-sectional area to sidewall area. We compared circular, square, triangular, and hexagonal cross-sectional shapes in this study. To date, nanorod LEDs with circular cross sections have been mainly demonstrated experimentally. However, circular shapes were found to show the lowest LEE, which is attributed to the coupling with whispering-gallery modes. For the total emission of the nanorod, the triangular cross section exhibited the highest LEE. When the angular dependence of the LEE was calculated using the FFP simulation results, the triangular and hexagonal shapes showed relatively high LEEs for direction emission. The simulation results presented in this study are expected to be useful in designing high-efficiency nanorod LED structures with optimum nanorod shape and dimensions. Full article
(This article belongs to the Special Issue Group-III Nitride Quantum Wells)
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31 pages, 9156 KiB  
Review
Review on Crystallization Strategies for Polymer Single Crystals
by Tianyu Wu, Jun Xu and Haimu Ye
Crystals 2024, 14(3), 207; https://doi.org/10.3390/cryst14030207 - 22 Feb 2024
Cited by 4 | Viewed by 6861
Abstract
Polymer physics has evolved significantly over the past century, transitioning from the early recognition of the chain structure of polymers to a mature field integrating principles from statistical mechanics, thermodynamics, and condensed matter physics. As an important part of polymer physics, polymer single [...] Read more.
Polymer physics has evolved significantly over the past century, transitioning from the early recognition of the chain structure of polymers to a mature field integrating principles from statistical mechanics, thermodynamics, and condensed matter physics. As an important part of polymer physics, polymer single crystals are crucial for understanding molecular structures and behaviors, enhancing material properties, and enabling precise functionalization. They offer insights into polymer crystallization kinetics, serve as templates for nanofabrication, and have applications in electronics, sensors, and biomedical fields. However, due to the complexity of molecular chain movement, the formation of polymer single crystals is still very difficult. Over the decades, numerous researchers have dedicated themselves to unraveling the mysteries of polymer single crystals, yielding substantial findings. This paper focus on the historical evolution and advancements in polymer single crystal research, aiming to offer valuable insights and assistance to fellow researchers in this field. Full article
(This article belongs to the Special Issue Advanced Research on Macromolecular Crystals (2nd Edition))
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12 pages, 3502 KiB  
Article
The Role of Diamonds Dispersed in Ferronematic Liquid Crystals on Structural Properties
by Peter Bury, Marek Veveričík, František Černobila, Natália Tomašovičová, Veronika Lacková, Katarína Kónyová, Ivo Šafařík, Viktor Petrenko, Oleksandr Tomchuk, Milan Timko and Peter Kopčanský
Crystals 2024, 14(3), 202; https://doi.org/10.3390/cryst14030202 - 20 Feb 2024
Viewed by 1497
Abstract
A study of the role of diamond nanoparticles on 5CB liquid crystal composites with Fe3O4 nanoparticles is presented. Composite ferronematic systems based on the nematic liquid crystal 5CB doped with Fe3O4 magnetic nanoparticles and additionally bound to [...] Read more.
A study of the role of diamond nanoparticles on 5CB liquid crystal composites with Fe3O4 nanoparticles is presented. Composite ferronematic systems based on the nematic liquid crystal 5CB doped with Fe3O4 magnetic nanoparticles and additionally bound to diamond nanoparticles (DNPs), of a volume concentration of 3.2 mg/mL, 1.6 mg/mL and 0.32 mg/mL, were investigated using both magneto-optical effect and surface acoustic waves (SAWs) to study the role of diamond nanoparticles on the structural properties of ferronematic liquid crystals. The responses of light transmission and SAW attenuation to an external magnetic field were investigated experimentally under a linearly increasing and decreasing magnetic field, respectively. Investigations of the phase transition temperature shift of individual composites were also performed. The experimental results highlighted a decrease in the threshold field in the ferronematic LC composites compared to the pure 5CB as well as its further decrease after mixing Fe3O4 with diamond powder. Concerning the transition temperature, its increase with an increase in the volume fraction of both kinds of nanoparticles was registered. The role of diamond nanoparticles in the structural changes and the large residual light transition and/or attenuation (memory effect) were also observed. The presented results confirmed the potential of diamond nanoparticles in nematic composites to modify their properties which could lead to final applications. Full article
(This article belongs to the Section Liquid Crystals)
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14 pages, 4544 KiB  
Article
The Crystal Structure and Physicochemical Properties of New Complexes Containing a CuII-LnIII-CuII Core
by Beata Cristóvão, Dariusz Osypiuk and Barbara Mirosław
Crystals 2024, 14(2), 189; https://doi.org/10.3390/cryst14020189 - 14 Feb 2024
Cited by 1 | Viewed by 1609
Abstract
Three new cationic complexes, [Cu4Tb2(H2L)4(NO3)4(H2O)3](NO3)2·5.5H2O·2MeOH (1), [Cu4Ho2(H2L)4(NO3)4(H [...] Read more.
Three new cationic complexes, [Cu4Tb2(H2L)4(NO3)4(H2O)3](NO3)2·5.5H2O·2MeOH (1), [Cu4Ho2(H2L)4(NO3)4(H2O)3](NO3)2·7.5H2O (2), and [Cu4Er2(H2 L)4(NO3)4(H2O)3](NO3)2·7H2O·3MeOH (3), were synthesized and studied using elemental and TG/DTG/DSC analyses, single-crystal X-ray diffraction, and magnetic measurements. The structure analysis showed that 1–3 crystallize as (NO3)-bridged compounds and that the lanthanide(III) ion acts as a joint connecting two [CuH2L] coordination units. In each heterotrinuclear unit, an asymmetry in the degree of planarity of the bridging CuO2Ln fragments is observed. The CuII ions are five- and six-coordinate, with distorted square pyramidal and octahedral geometry, respectively, whereas the LnIII ions are nine-coordinate. The solvates 1–3 are stable at room temperature, and their desolvation process is consistent with the loss of water and/or methanol molecules. The temperature dependence of the magnetic susceptibility and the field-dependent magnetization indicate the weak ferromagnetic interaction between the paramagnetic centers CuII and TbIII/HoIII 1 and 2. Full article
(This article belongs to the Special Issue Feature Papers in Crystals 2023)
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12 pages, 3721 KiB  
Article
Combining a Drug and a Nutraceutical: A New Cocrystal of Praziquantel and Curcumin
by Camila Caro Garrido, Marie Vandooren, Koen Robeyns, Damien P. Debecker, Patricia Luis and Tom Leyssens
Crystals 2024, 14(2), 181; https://doi.org/10.3390/cryst14020181 - 11 Feb 2024
Cited by 4 | Viewed by 2404
Abstract
This study explores the co-crystallization between the drug praziquantel (PZQ) and the nutraceutical curcumin (CU). The investigation revealed two novel solid forms: a cocrystal solvate with ethyl acetate and a non-solvated cocrystal. This novel drug–nutraceutical cocrystal is a praziquantel–curcumin (2:1) cocrystal. The cocrystal [...] Read more.
This study explores the co-crystallization between the drug praziquantel (PZQ) and the nutraceutical curcumin (CU). The investigation revealed two novel solid forms: a cocrystal solvate with ethyl acetate and a non-solvated cocrystal. This novel drug–nutraceutical cocrystal is a praziquantel–curcumin (2:1) cocrystal. The cocrystal solvate has ethyl acetate molecules occupying the voids with minimal interactions within the crystal lattice. The application of heat treatment induces solvent removal and prompts the transition to the non-solvated cocrystal, as highlighted by variable-temperature X-ray powder diffraction (VT-XRPD). Thermal analyses demonstrate the stability of the cocrystal solvate up to approximately 100 °C, beyond which it transforms into the non-solvated phase, which eventually melts at 130 °C. Full article
(This article belongs to the Special Issue Feature Papers in Crystals 2023)
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14 pages, 3787 KiB  
Article
Investigating Influential Parameters for High-Purity Germanium Crystal Growth
by Sanjay Bhattarai, Dongming Mei, Narayan Budhathoki, Kunming Dong and Austin Warren
Crystals 2024, 14(2), 177; https://doi.org/10.3390/cryst14020177 - 10 Feb 2024
Viewed by 2545
Abstract
This paper focuses on the research and development of high-purity germanium (HPGe) crystals for detector fabrication, specifically targeting applications in rare-event physics searches. The primary objective was to produce large-scale germanium crystals weighing >1 kg with a controlled diameter of ∼10 cm and [...] Read more.
This paper focuses on the research and development of high-purity germanium (HPGe) crystals for detector fabrication, specifically targeting applications in rare-event physics searches. The primary objective was to produce large-scale germanium crystals weighing >1 kg with a controlled diameter of ∼10 cm and an impurity range of approximately 1010/cm 3. Ensuring structural integrity and excellent crystalline quality requires a thorough assessment of dislocation density, a critical aspect of the crystal development process. Dislocation density measurements play a crucial role in maximizing the sensitivity of HPGe detectors, and our findings confirmed that the dislocation density fell within acceptable ranges for detector fabrication. Additionally, this paper examines the segregation coefficient of various contaminants during the crystal development process. Comprehensive analysis of impurity segregation is essential for reducing contaminant quantities in the crystal lattice and customizing purification processes. This, in turn, minimizes undesired background noise, enhancing signal-to-noise ratios for rare-event physics searches and overall detector performance. The investigation included the segregation coefficients of three major acceptors and one donor in crystals grown at the University of South Dakota, providing valuable insights for optimizing crystal purity and detector efficiency. Full article
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18 pages, 7567 KiB  
Article
Numerical Microstructure Prediction for Lattice Structures Manufactured by Electron Beam Powder Bed Fusion
by Johannes A. Koepf, Julian Pistor, Matthias Markl and Carolin Körner
Crystals 2024, 14(2), 149; https://doi.org/10.3390/cryst14020149 - 31 Jan 2024
Cited by 4 | Viewed by 1494
Abstract
The latest advances in additive manufacturing have given rise to an increasing interest in additively built lattice structures due to their superior properties compared to foams and honeycombs. The foundation of these superior properties is a tailored microstructure, which is difficult to achieve [...] Read more.
The latest advances in additive manufacturing have given rise to an increasing interest in additively built lattice structures due to their superior properties compared to foams and honeycombs. The foundation of these superior properties is a tailored microstructure, which is difficult to achieve in additive manufacturing because of the variety of process parameters influencing the quality of the final part. This work presents the numerical prediction of the resulting grain structure of a lattice structure additively built by electron beam powder bed fusion. A thermal finite-difference model is coupled to a sophisticated cellular automaton-based crystal growth model, including nucleation. Numerically predicted grain structures, considering different nucleation conditions, are compared with experimentally derived EBSD measurements. The comparison reveals that nucleation is important, especially in fine lattice structures. The developed software, utilizing the nucleation model, is finally able to predict the as-built grain structure in lattice structures. Full article
(This article belongs to the Special Issue Crystallization Process and Simulation Calculation, Second Edition)
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22 pages, 8785 KiB  
Article
Insights in the Structural Hierarchy of Statically Crystallized Palm Oil
by Fien De Witte, Ivana A. Penagos, Kato Rondou, Kim Moens, Benny Lewille, Daylan A. Tzompa-Sosa, Davy Van de Walle, Filip Van Bockstaele, Andre G. Skirtach and Koen Dewettinck
Crystals 2024, 14(2), 142; https://doi.org/10.3390/cryst14020142 - 30 Jan 2024
Cited by 4 | Viewed by 2282
Abstract
Palm oil (PO) is still widely used for the production of all types of food products. Due to its triacylglycerol (TG) composition, PO is semisolid at ambient temperature, offering possibilities for many applications. In order to tailor the fat crystal network for certain [...] Read more.
Palm oil (PO) is still widely used for the production of all types of food products. Due to its triacylglycerol (TG) composition, PO is semisolid at ambient temperature, offering possibilities for many applications. In order to tailor the fat crystal network for certain applications, it remains imperative to understand the structural build-up of the fat crystal network at the full-length scale and to understand the effect of processing conditions. In this study, PO was crystallized under four temperature protocols (fast (FC) or slow (SC) cooling to 20 °C or 25 °C) and was followed for one hour of isothermal time. A broad toolbox was used to fundamentally unravel the structural build-up of the fat crystal network at different length scales. Wide-angle and small-angle X-ray scattering (WAXS and SAXS) showed transitions from α-2L to β’-2L over time. Despite the presence of the same polymorphic form (β’), chain length structure (2L), and domain size, ultra-small-angle X-ray scattering (USAXS) showed clear differences in the mesoscale. For all samples, the lamellar organization was confirmed. Both cooling speed and isothermal temperature were found to affect the size of the crystal nanoplatelets (CNPs), where the highest cooling speed and lowest isothermal temperature (FC and 20 °C) created the smallest CNPs. The microstructure was visualized with polarized light microscopy (PLM) and cryo-scanning electron microscopy (cryo-SEM), showing clear differences in crystallite size, clustering, and network morphology. Raman spectroscopy was applied to confirm differences in triglyceride distribution in the fat crystal network. This study shows that both cooling rate and isothermal temperature affect the fat crystal network formed, especially at the meso- and microscale. Full article
(This article belongs to the Special Issue Feature Papers in Crystals 2023)
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20 pages, 7575 KiB  
Article
Lattice Parameter Evolution during the β-to-α and β-to-ω Transformations of Iron- and Aluminum-Modified Ti-11Cr(at.%)
by JoAnn Ballor, Jonathan D. Poplawsky, Arun Devaraj, Scott Misture and Carl J. Boehlert
Crystals 2024, 14(2), 145; https://doi.org/10.3390/cryst14020145 - 30 Jan 2024
Cited by 1 | Viewed by 1872
Abstract
β-titanium (β-Ti) alloys are useful in diverse industries because their mechanical properties can be tuned by transforming the metastable β phase into other metastable and stable phases. Relationships between lattice parameter and β-Ti alloy concentrations have been explored, but the lattice parameter evolution [...] Read more.
β-titanium (β-Ti) alloys are useful in diverse industries because their mechanical properties can be tuned by transforming the metastable β phase into other metastable and stable phases. Relationships between lattice parameter and β-Ti alloy concentrations have been explored, but the lattice parameter evolution during β-phase transformations is not well understood. In this work, the β-Ti alloys, Ti-11Cr, Ti-11Cr-0.85Fe, Ti-11Cr-5.3Al, and Ti-11Cr-0.85Fe-5.3Al (all in at.%), underwent a 400 °C aging treatment for up to 12 h to induce the β-to-ω and β-to-α phase transformations. Phase identification and lattice parameters were measured in situ using high-temperature X-ray diffraction. Phase compositions were measured ex situ using atom probe tomography. During the phase transformations, Cr and Fe diffused from the ω and α phases into the β matrix, and the β-phase lattice parameter exhibited a corresponding decrease. The decrease in β-phase lattice parameter affected the α- and ω-phase lattice parameters. The α phase in the Fe-free alloys exhibited α-phase c/a ratios close to those of pure Ti. A larger β-phase composition change in Ti-11Cr resulted in larger ω-phase lattice parameter changes than that for Ti-11Cr-0.85Fe. This work illuminates the complex relationship between diffusion, composition, and structure for these diffusive/displacive transformations. Full article
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21 pages, 10223 KiB  
Article
Kinetics and Thermodynamics of the Phase Transformation in the Nanocrystalline Substance—Gas Phase System
by Walerian Arabczyk, Rafał Pelka, Bartłomiej Wilk and Zofia Lendzion-Bieluń
Crystals 2024, 14(2), 129; https://doi.org/10.3390/cryst14020129 - 27 Jan 2024
Cited by 2 | Viewed by 1239
Abstract
This study presents a model of the reaction of a nanocrystalline substance within the gas phase, where diffusion of gas reactants in the volume of the nanocrystallites is a rate-limiting step. According to the model calculations carried out, the rate of diffusion across [...] Read more.
This study presents a model of the reaction of a nanocrystalline substance within the gas phase, where diffusion of gas reactants in the volume of the nanocrystallites is a rate-limiting step. According to the model calculations carried out, the rate of diffusion across the phase boundary located on the nanocrystallite surface limits the rate of the process. It was stated that in chemical processes with a phase transformation, the critical concentration of absorbate depends on two factors: the specific active surface area of the adsorbent and the difference in chemical potentials between the gas phase and the equilibrium potential at which the phase transformation occurs. When the actual adsorbate potential in the gas phase is much greater than the equilibrium potential of the nanocrystallite with the largest specific active surface, nanocrystallites undergo phase changes in the order according to their specific active surfaces from the largest to the smallest. In a process where the actual adsorbate potential is close to an equilibrium one, nanocrystallites undergo phase transformation in the order of their specific active surface from the smallest to the largest. Full article
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16 pages, 2497 KiB  
Article
Halogen Bonding versus Nucleophilic Substitution in the Co-Crystallization of Halomethanes and Amines
by Olivia Grounds, Matthias Zeller and Sergiy V. Rosokha
Crystals 2024, 14(2), 124; https://doi.org/10.3390/cryst14020124 - 26 Jan 2024
Cited by 3 | Viewed by 1838
Abstract
Haloalkanes and amines are common halogen-bond (XB) donors and acceptors as well as typical reagents in nucleophilic substitution reactions. Thus, crystal engineering using these molecules requires an understanding of the interchange between these processes. Indeed, we previously reported that the interaction of quinuclidine [...] Read more.
Haloalkanes and amines are common halogen-bond (XB) donors and acceptors as well as typical reagents in nucleophilic substitution reactions. Thus, crystal engineering using these molecules requires an understanding of the interchange between these processes. Indeed, we previously reported that the interaction of quinuclidine (QN) with CHI3 in acetonitrile yielded co-crystals showing a XB network of these two constituents. In the current work, the interactions of QN with C2H5I or 1,4-diazabicyclo[2.2.2]octane (DABCO) with CH2I2 led to nucleophilic substitution producing I− anions and quaternary ammonium (QN-CH2CH3 or DABCO-CH2I+) cations. Moreover, the reaction of QN with CHI3 in dichloromethane afforded co-crystals containing XB networks of CHI3 with either Cl− or I− anions and QN-CH2Cl+ counter-ions. A similar reaction in acetone produced XB networks comprising CHI3, I− and QN-CH2COCH3+. These distinctions were rationalized through a computational analysis of XB complexes and the transition-state energies for the nucleophilic substitution. It indicated that the outcome of the reactions was determined mostly by the relative energies of the products. The co-crystals obtained in this work showed bonding between the cationic (DABCO-CH2I+, QN-CH2Cl+) or neutral (CHI3) XB donors and the anionic (I−, Cl−) or neutral (CHI3) acceptors. Their analysis showed comparable electron and energy densities at the XB bond critical points and similar XB energies regardless of the charges of the interacting species. Full article
(This article belongs to the Special Issue Feature Papers in Crystals 2023)
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29 pages, 14422 KiB  
Review
Advances in Ultrasonic-Assisted Directed Energy Deposition (DED) for Metal Additive Manufacturing
by Wenjun Zhang, Chunguang Xu, Cencheng Li and Sha Wu
Crystals 2024, 14(2), 114; https://doi.org/10.3390/cryst14020114 - 24 Jan 2024
Cited by 12 | Viewed by 4608
Abstract
Directed Energy Deposition (DED), a branch of AM processes, has emerged as a significant technique for fabricating large metal components in sectors such as aerospace, automotive, and healthcare. DED is characterized by its high deposition rate and scalability, which stand out among other [...] Read more.
Directed Energy Deposition (DED), a branch of AM processes, has emerged as a significant technique for fabricating large metal components in sectors such as aerospace, automotive, and healthcare. DED is characterized by its high deposition rate and scalability, which stand out among other AM processes. However, it encounters critical issues such as residual stresses, distortion, porosity, and rough surfaces resulting from rapid melting and solidification. As a novel advancement, Ultrasonic-Assisted Directed Energy Deposition (UA-DED) integrates ultrasonic oscillations into DED aimed at addressing these challenges. Herein, the latest research related to the UA-DED process and the current major challenges of the DED process, residual stresses, porosity, and crack defects are critically reviewed. Subsequently, the paper also details the working principle and system components of UA-DED technology and reviews the material improvement by introducing UA into the DED process, grain, porosity, tensile properties, and deposition defects. The most critical optimization methods of process parameter variables for UA and the different material interaction mechanisms between UA and DED processes are identified and discussed in detail. Finally, the perspectives on the research gap and potential future developments in UA-DED are also discussed. Full article
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16 pages, 6028 KiB  
Article
Insights into the Spray Synthesis of UiO-66 and UiO-66-NH2 Metal–Organic Frameworks: Effect of Zirconium Precursors and Process Parameters
by Masaru Kubo, Yusuke Miyoshi, Yushi Uchitomi and Manabu Shimada
Crystals 2024, 14(2), 116; https://doi.org/10.3390/cryst14020116 - 24 Jan 2024
Cited by 4 | Viewed by 3318
Abstract
UiO-66, a zirconium-based metal–organic framework, was synthesized using a one-step spray synthesis method to investigate the effects of preheating the precursor solution and Zr sources on crystallinity. Using ZrCl4 with water as a modulator requires preheating at 80 °C for 120 min [...] Read more.
UiO-66, a zirconium-based metal–organic framework, was synthesized using a one-step spray synthesis method to investigate the effects of preheating the precursor solution and Zr sources on crystallinity. Using ZrCl4 with water as a modulator requires preheating at 80 °C for 120 min or 120 °C for 30 min for the spray synthesis of UiO-66 to form secondary building units (SBUs). By contrast, the use of Zr(OnPr)4 with acetic acid (AcOH) as a modulator allowed the spray synthesis of UiO-66 and UiO-66-NH2 without preheating because of the rapid formation of SBUs with AcOH. The spray-synthesized UiO-66 using Zr(OnPr)4 exhibited a BET surface area of 1258 m2/g and a CO2 adsorption capacity of 3.43 mmol/g at 273 K and 1 bar, while UiO-66-NH2 exhibited a BET surface area of 1263 m2/g and a CO2 adsorption capacity of 6.11 mmol/g under the same conditions. Full article
(This article belongs to the Section Hybrid and Composite Crystalline Materials)
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16 pages, 7643 KiB  
Article
Combustion Synthesis of Zirconium-Doped Ceria Nanocatalyst
by Katarina Mužina, Stanislav Kurajica, Helena Bach-Rojecky, Filip Brleković and Marina Duplančić
Crystals 2024, 14(2), 108; https://doi.org/10.3390/cryst14020108 - 23 Jan 2024
Cited by 1 | Viewed by 2255
Abstract
Zirconium-doped ceria is a promising and extensively researched catalytic material with notable use in three-way catalytic converters, the oxidation of volatile organic compounds and solid oxide fuel cells. In this work, pure and zirconium-doped ceria nanoparticles (Ce1−xZrxO2, [...] Read more.
Zirconium-doped ceria is a promising and extensively researched catalytic material with notable use in three-way catalytic converters, the oxidation of volatile organic compounds and solid oxide fuel cells. In this work, pure and zirconium-doped ceria nanoparticles (Ce1−xZrxO2, where x = 0, 0.1, 0.2, and 0.3) were prepared by combustion synthesis using glycine as the fuel and cerium and zirconium nitrate as oxidants. The obtained powders were characterized using X-ray powder diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, differential thermal and thermogravimetric analysis, UV–Vis diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. The combustion temperature increases with the increase in zirconium content in the samples, but the XRD patterns exclusively show ceria diffraction peaks. The crystallite sizes are in the range from 25.2 to 11.7 nm, and do not vary substantially after thermal treatment, indicating the good thermal stability of the prepared nanocatalysts. XPS analysis showed that the surface amount of zirconium is lower than the nominal and that the ceria sample with 10 mol. % of zirconium has a higher amount of oxygen vacancies than the 30 mol. % Zr-doped sample. The 10 mol. % Zr-doped sample displays the best catalytic activity in the BTEX (benzene, toluene, ethylbenzene, and o-xylene) oxidation process. Full article
(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization)
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26 pages, 4510 KiB  
Review
Crystal Engineering of Hydrogen Bonding for Direct Air Capture of CO2: A Quantum Crystallography Perspective
by Sylwia Pawlędzio and Xiaoping Wang
Crystals 2024, 14(1), 77; https://doi.org/10.3390/cryst14010077 - 13 Jan 2024
Cited by 2 | Viewed by 2900
Abstract
Rising atmospheric CO2 levels demand efficient and sustainable carbon capture solutions. Direct air capture (DAC) via crystallizing hydrogen-bonded frameworks such as carbonate salts has emerged as a promising approach. This review explores the potential of crystal engineering, in tandem with advanced quantum [...] Read more.
Rising atmospheric CO2 levels demand efficient and sustainable carbon capture solutions. Direct air capture (DAC) via crystallizing hydrogen-bonded frameworks such as carbonate salts has emerged as a promising approach. This review explores the potential of crystal engineering, in tandem with advanced quantum crystallography techniques and computational modeling, to unlock the full potential of DAC materials. We examine the critical role of hydrogen bonding and other noncovalent interactions within a family of bis-guanidines that governs the formation of carbonate salts with high CO2 capture capacity and low regeneration energies for utilization. Quantum crystallography and charge density analysis prove instrumental in elucidating these interactions. A case study of a highly insoluble carbonate salt of a 2,6-pyridine-bis-(iminoguanidine) exemplifies the effectiveness of these approaches. However, challenges remain in the systematic and precise determination of hydrogen atom positions and atomic displacement parameters within DAC materials using quantum crystallography, and limitations persist in the accuracy of current energy estimation models for hydrogen bonding interactions. Future directions lie in exploring diverse functional groups, designing advanced hydrogen-bonded frameworks, and seamlessly integrating experimental and computational modeling with machine learning. This synergistic approach promises to propel the design and optimization of DAC materials, paving the way for a more sustainable future. Full article
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11 pages, 3171 KiB  
Article
Segregation of Phosphorus and Silicon at the Grain Boundary in Bcc Iron via Machine-Learned Force Fields
by Miroslav Černý and Petr Šesták
Crystals 2024, 14(1), 74; https://doi.org/10.3390/cryst14010074 - 12 Jan 2024
Cited by 1 | Viewed by 1541
Abstract
The study of the effects of impurity on grain boundaries is a critical aspect of materials science, particularly when it comes to understanding and controlling the properties of materials for specific applications. One of the related key issues is the segregation preference of [...] Read more.
The study of the effects of impurity on grain boundaries is a critical aspect of materials science, particularly when it comes to understanding and controlling the properties of materials for specific applications. One of the related key issues is the segregation preference of impurity atoms in the grain boundary region. In this paper, we employed the on-the-fly machine learning to generate force fields, which were subsequently used to calculate the segregation energies of phosphorus and silicon in bcc iron containing the ∑5(310)[001] grain boundary. The generated force fields were successfully benchmarked using ab initio data. Our further calculations considered impurity atoms at a number of possible interstitial and substitutional segregation sites. Our predictions of the preferred sites agree with the experimental observations. Planar concentration of impurity atoms affects the segregation energy and, moreover, can change the preferred segregation sites. Full article
(This article belongs to the Section Crystalline Metals and Alloys)
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9 pages, 2237 KiB  
Article
The Solid-Phase Transition of Carbapenem CS-023 Polymorphs and the Change in Helicity Observed in the Transition
by Shinji Matsuura, Koichi Igarashi, Masayuki Azuma and Hiroshi Ooshima
Crystals 2024, 14(1), 71; https://doi.org/10.3390/cryst14010071 - 11 Jan 2024
Cited by 1 | Viewed by 1238
Abstract
Anti-solvent crystallization of carbapenem CS-023 was performed at 25 °C. The following results were obtained: (1) A solvate crystal, Form A (5/2 Ethanol·1/2 H2O), was recovered from 80 v/v% ethanol solution; (2) Form A transformed to Form H [...] Read more.
Anti-solvent crystallization of carbapenem CS-023 was performed at 25 °C. The following results were obtained: (1) A solvate crystal, Form A (5/2 Ethanol·1/2 H2O), was recovered from 80 v/v% ethanol solution; (2) Form A transformed to Form H (4H2O) through solid-phase transition through the solvate-free polymorph, Form A-2, and Form A also transformed into Form C (1Ethanol·3H2O) through solvent-mediated transformation. In the present study, we found that Form C also transforms to Form H through the solid-phase transition through the solvate-free polymorph Form C-2. The three polymorphs, Forms A, H, and C, were composed of helical chain structures. However, there was an incomprehensible affair in the solid-phase transition among the three polymorphs. Namely, Form A comprised a left-handed helix. On the other hand, Form C’s and Form H’s helix chains were in a left- and right-handed helix complex, respectively. The solid-phase transition of Form A into Form H suggested a switch in helicity in the solid. We attempted to explain the helicity change in the solid-phase transition. As a result, we suggest that the over-absorption of water by Form A-2 at high humidity plays a vital role in the helicity change. Full article
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12 pages, 3041 KiB  
Article
Monitoring of Carbonated Hydroxyapatite Growth on Modified Polycrystalline CVD-Diamond Coatings on Titanium Substrates
by Rocco Carcione, Valeria Guglielmotti, Francesco Mura, Silvia Orlanducci and Emanuela Tamburri
Crystals 2024, 14(1), 66; https://doi.org/10.3390/cryst14010066 - 6 Jan 2024
Cited by 2 | Viewed by 1940
Abstract
Production of diamond coatings on titanium substrates has demonstrated as a promising strategy for applications ranging from biosensing to hard tissue engineering. The present study focuses on monitoring the nucleation and growth of bone-like carbonated-hydroxyapatite (C-HA) on polycrystalline diamond (PCD) synthetized on titanium [...] Read more.
Production of diamond coatings on titanium substrates has demonstrated as a promising strategy for applications ranging from biosensing to hard tissue engineering. The present study focuses on monitoring the nucleation and growth of bone-like carbonated-hydroxyapatite (C-HA) on polycrystalline diamond (PCD) synthetized on titanium substrate by means of a hot filament chemical vapor deposition (HF-CVD) method. The surface terminations of diamond coatings were selectively modified by oxidative treatments. The process of the C-HA deposition, accomplished by precipitation from simulated body fluid (SBF), was monitored from 3 to 20 days by Raman spectroscopy analysis. The coupling of morphological and structural investigations suggests that the modulation of the PCD surface chemistry enhances the bioactivity of the produced materials, allowing for the formation of continuous C-HA coatings with needle-like texture and chemical composition typical of those of the bone mineral. Specifically, after 20 days of immersion in SBF the calculated carbonate weight percent and the Ca/P ratio are 5.5% and 2.1, respectively. Based on these results, this study brings a novelty in tailoring the CVD-diamond properties for advanced biomedical and technological applications. Full article
(This article belongs to the Special Issue Poly-Crystalline/Single-Crystalline Diamonds)
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19 pages, 10482 KiB  
Article
Transferring Crystallization Conditions from Small to Larger Scale for Achieving Targeted Crystal Morphologies of an Active Pharmaceutical Ingredient
by Nicolás Antonio Ramos Ojeda and Matthias Kind
Crystals 2024, 14(1), 42; https://doi.org/10.3390/cryst14010042 - 28 Dec 2023
Cited by 2 | Viewed by 2228
Abstract
Crystal morphology plays a critical role in the processability and physicochemical behavior of active pharmaceutical ingredients. Manipulating crystal morphology involves consideration of crystallization conditions such as temperature, supersaturation, and solvent choice. Typically, experimental screenings on a small scale are conducted to find targeted [...] Read more.
Crystal morphology plays a critical role in the processability and physicochemical behavior of active pharmaceutical ingredients. Manipulating crystal morphology involves consideration of crystallization conditions such as temperature, supersaturation, and solvent choice. Typically, experimental screenings on a small scale are conducted to find targeted crystal morphologies. However, results from such small-scale experiments do not assure direct success at a larger scale, particularly if the small-scale setup differs significantly from a conventional stirred crystallizator. In this study, we successfully validated the morphologies observed in the small-scale experiments of an exemplary API, Bitopertin, when scaled up by a factor of 200, through the maintenance of identical process conditions and geometrical vessel relations. This successful scalability highlights the significant potential of small-scale crystallization studies to provide a reliable foundation for further exploration in large-scale endeavors. Full article
(This article belongs to the Section Crystal Engineering)
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11 pages, 884 KiB  
Article
One-Dimensional Gap Soliton Molecules and Clusters in Optical Lattice-Trapped Coherently Atomic Ensembles via Electromagnetically Induced Transparency
by Zhiming Chen, Hongqiang Xie, Qi Zhou and Jianhua Zeng
Crystals 2024, 14(1), 36; https://doi.org/10.3390/cryst14010036 - 27 Dec 2023
Viewed by 1420
Abstract
In past years, optical lattices have been demonstrated as an excellent platform for making, understanding, and controlling quantum matters at nonlinear and fundamental quantum levels. Shrinking experimental observations include matter-wave gap solitons created in ultracold quantum degenerate gases, such as Bose–Einstein condensates with [...] Read more.
In past years, optical lattices have been demonstrated as an excellent platform for making, understanding, and controlling quantum matters at nonlinear and fundamental quantum levels. Shrinking experimental observations include matter-wave gap solitons created in ultracold quantum degenerate gases, such as Bose–Einstein condensates with repulsive interaction. In this paper, we theoretically and numerically study the formation of one-dimensional gap soliton molecules and clusters in ultracold coherent atom ensembles under electromagnetically induced transparency conditions and trapped by an optical lattice. In numerics, both linear stability analysis and direct perturbed simulations are combined to identify the stability and instability of the localized gap modes, stressing the wide stability region within the first finite gap. The results predicted here may be confirmed in ultracold atom experiments, providing detailed insight into the higher-order localized gap modes of ultracold bosonic atoms under the quantum coherent effect called electromagnetically induced transparency. Full article
(This article belongs to the Topic Mathematical Applications of Nonlinear Wave Properties in Crystalline and Dispersive Media)
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11 pages, 8281 KiB  
Article
Structural and Electrochemical Properties of F-Doped RbTiOPO4 (RTP:F) Predicted from First Principles
by Adriana Bocchini, Yingjie Xie, Wolf Gero Schmidt and Uwe Gerstmann
Crystals 2024, 14(1), 5; https://doi.org/10.3390/cryst14010005 - 20 Dec 2023
Cited by 1 | Viewed by 1447
Abstract
Batteries based on heavier alkali ions are considered promising candidates to substitute for current Li-based technologies. In this theoretical study, we characterize the structural properties of a novel material, i.e., F-doped RbTiOPO4 (RbTiPO4F, RTP:F), and discuss aspects of its electrochemical [...] Read more.
Batteries based on heavier alkali ions are considered promising candidates to substitute for current Li-based technologies. In this theoretical study, we characterize the structural properties of a novel material, i.e., F-doped RbTiOPO4 (RbTiPO4F, RTP:F), and discuss aspects of its electrochemical performance in Rb-ion batteries (RIBs) using density functional theory (DFT). According to our calculations, RTP:F is expected to retain the so-called KTiOPO4 (KTP)-type structure, with lattice parameters of 13.236 Å, 6.616 Å, and 10.945 Å. Due to the doping with F, the crystal features eight extra electrons per unit cell, whereby each of these electrons is trapped by one of the surrounding Ti atoms in the cell. Notably, the ground state of the system corresponds to a ferromagnetic spin configuration (i.e., S=4). The deintercalation of Rb leads to the oxidation of the Ti atoms in the cell (i.e., from Ti3+ to Ti4+) and to reduced magnetic moments. The material promises interesting electrochemical properties for the cathode: rather high average voltages above 2.8 V and modest volume shrinkages below 13% even in the fully deintercalated case are predicted. Full article
(This article belongs to the Special Issue New Materials for Electrochemical Energy Storage Systems and Catalysis)
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13 pages, 1940 KiB  
Article
Study on the Growth and Regulation of Large-Particle Sr(OH)2·8H2O Crystals with Process Analytical Technology
by Binbin Shi, Yongjuan Zhang, Shudong Liang, Yanan Wang, Yan Jing, Xingwu Zou and Xuezhong Wang
Crystals 2024, 14(1), 4; https://doi.org/10.3390/cryst14010004 - 20 Dec 2023
Viewed by 1564
Abstract
Sr(OH)2 is an indispensable strontium compound extensively harnessed in sugar refining, strontium lubricating wax formulation, and polymer plastic stabilization. Sr(OH)2·8H2O is the prevalent hydrate form of Sr(OH)2. Deprived of moisture via vacuum drying, Sr(OH)2 can [...] Read more.
Sr(OH)2 is an indispensable strontium compound extensively harnessed in sugar refining, strontium lubricating wax formulation, and polymer plastic stabilization. Sr(OH)2·8H2O is the prevalent hydrate form of Sr(OH)2. Deprived of moisture via vacuum drying, Sr(OH)2 can be procured from Sr(OH)2·8H2O. Sr(OH)2·8H2O particles with larger sizes exhibit impressive attributes such as facile solid–liquid divergence, elevated product purity, expedient drying, and resilience to agglomeration, which have garnered significant interest. Given the superior quality of the product and the dependability of the process, process analytical technology (PAT) has been extensively employed in the pharmaceutical sector, rendering it feasible to employ PAT to fabricate large-particle Sr(OH)2·8H2O crystals. This study utilizes industrial SrCO3 to prepare high-purity Sr(OH)2·8H2O with a purity of over 99.5%. The growth process of single crystals was observed using a hot-stage microscope, and the growth process of large-particle Sr(OH)2·8H2O was optimized and regulated online using PAT. The optimal process conditions were optimized, and large-particle Sr(OH)2·8H2O crystals were obtained by adding crystal seeds. On this basis, we proposed a seed control mechanism for Sr(OH)2·8H2O. Full article
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15 pages, 6390 KiB  
Article
Sol–Gel Synthesis of ZnO:Li Thin Films: Impact of Annealing on Structural and Optical Properties
by Tatyana Ivanova, Antoaneta Harizanova, Tatyana Koutzarova, Benedicte Vertruyen and Raphael Closset
Crystals 2024, 14(1), 6; https://doi.org/10.3390/cryst14010006 - 20 Dec 2023
Cited by 3 | Viewed by 2276
Abstract
A sol–gel deposition approach was applied for obtaining nanostructured Li-doped ZnO thin films. ZnO:Li films were successfully spin-coated on quartz and silicon substrates. The evolution of their structural, vibrational, and optical properties with annealing temperature (300–600 °C) was studied by X-ray diffraction (XRD), [...] Read more.
A sol–gel deposition approach was applied for obtaining nanostructured Li-doped ZnO thin films. ZnO:Li films were successfully spin-coated on quartz and silicon substrates. The evolution of their structural, vibrational, and optical properties with annealing temperature (300–600 °C) was studied by X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), UV-VIS spectroscopic, and field emission scanning electron microscopic (FESEM) characterization techniques. It was found that lithium doping maintains the wurtzite arrangement of ZnO, with increasing crystallite sizes when increasing the annealing temperature. Analysis of the FTIR spectra revealed a broad main absorption band (around 404 cm−1) for Li-doped films, implying the inclusion of Li into the ZnO lattice. The ZnO:Li films were transparent, with slightly decreased transmittance after the use of higher annealing temperatures. The porous network of undoped ZnO films was transformed to a denser, grained, packed structure, induced by lithium doping. Full article
(This article belongs to the Special Issue Advances in Synthesis, Characterization, and Application of Thin Films)
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15 pages, 5055 KiB  
Review
Impact of Structural Strain in Perovskite Epitaxial Thin Films on Their Functional Properties
by Florin Andrei, Maria Dinescu, Valentin Ion, Floriana Craciun, Ruxandra Birjega and Nicu Doinel Scarisoreanu
Crystals 2023, 13(12), 1686; https://doi.org/10.3390/cryst13121686 - 14 Dec 2023
Cited by 1 | Viewed by 2052
Abstract
The strain engineering effects induced by different means, e.g., the substrate lattice mismatch and/or chemical doping, on the functional properties of perovskite thin films have triggered interest in the use of these materials in different applications such as energy storage/generation or photonics. The [...] Read more.
The strain engineering effects induced by different means, e.g., the substrate lattice mismatch and/or chemical doping, on the functional properties of perovskite thin films have triggered interest in the use of these materials in different applications such as energy storage/generation or photonics. The effects of the film’s thickness and strain state of the structure for the lead-free perovskite ferrite-based materials (BiFeO3-BFO; Y-doped BiFeO3-BYFO; LaFeO3-LFO) on their functional properties are highlighted here. As was previously demonstrated, the dielectric properties of BFO epitaxial thin films are strongly affected by the film thickness and by the epitaxial strain induced by the lattice mismatch between substrate and film. Doping the BiFeO3 ferroelectric perovskite with rare-earth elements or inducing a high level of structural deformation into the crystalline structure of LaFeO3 thin films have allowed the tuning of functional properties of these materials, such as dielectric, optical or photocatalytic ones. These changes are presented in relation to the appearance of complex ensembles of nanoscale phase/nanodomains within the epitaxial films due to strain engineering. However, it is a challenge to maintain the same level of epitaxial strain present in ultrathin films (<10 nm) and to preserve or tune the positive effects in films of thicknesses usually higher than 30 nm. Full article
(This article belongs to the Special Issue Ferroelectric Materials)
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12 pages, 7096 KiB  
Article
Synthesis and Structural Characterization of Layered Ni+1/+2 Oxides Obtained by Topotactic Oxygen Release on Nd2−xSrxNiO4−δ Single Crystals
by Chavana Hareesh, Monica Ceretti, Philippe Papet, Alexeï Bosak, Martin Meven and Werner Paulus
Crystals 2023, 13(12), 1670; https://doi.org/10.3390/cryst13121670 - 9 Dec 2023
Cited by 1 | Viewed by 1773
Abstract
Layered nickelate oxides containing Ni1+/Ni2+ are isoelectronic to Cu2+/Cu3+ compounds and of present interest with respect to recent findings of superconductivity in a series of different compositions. It is thereby questionable why superconductivity is still rare to [...] Read more.
Layered nickelate oxides containing Ni1+/Ni2+ are isoelectronic to Cu2+/Cu3+ compounds and of present interest with respect to recent findings of superconductivity in a series of different compositions. It is thereby questionable why superconductivity is still rare to find in nickelates, compared to the much larger amount of superconducting cuprates. Anisotropic dz2 vs. dx2−y2 orbital occupation as well as interface-induced superconductivity are two of the main advanced arguments. We are here interested in investigating the feasibility of synthesizing layered nickelate-type oxides, where the Ni1+/Ni2+ ratio can be tuned by oxygen and/or cation doping. Our strategy is to synthesize Sr-doped n = 1 Ruddlesden–Popper type Nd2−xSrxNiO4+δ single crystals, which are then reduced by H2 gas, forming Nd2−xSrxNiO4−δ via a topotactic oxygen release at moderate temperatures. We report here on structural studies carried out on single crystals by laboratory and synchrotron diffraction using pixel detectors. We evidence the general possibility to obtain reduced single crystals despite their increased orthorhombicity. This must be regarded as a milestone to obtain single crystalline nickelate oxides, which further on contain charge-ordering of Ni1+/Ni2+, opening the access towards anisotropic properties. Full article
(This article belongs to the Special Issue High Temperature Superconductor)
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13 pages, 3179 KiB  
Article
O-Vacancy-Rich ε-MnO2 Synthesized at Hydrophobic Interface: An Efficient Fenton-like Catalyst for Removing Ciprofloxacin from Water
by Yulong Chen, Yuan Chi, Xiao Wu, Cong Lin, Tengfei Lin, Min Gao, Chunlin Zhao and Baisheng Sa
Crystals 2023, 13(12), 1664; https://doi.org/10.3390/cryst13121664 - 6 Dec 2023
Viewed by 1534
Abstract
The widespread use of pharmaceuticals and personal care products (PPCPs) in many fields has brought convenience to human lives but has also caused unavoidable environmental pollution issues. In particular, the resistance gene problem resulting from accumulating antibiotics that cannot be fully absorbed by [...] Read more.
The widespread use of pharmaceuticals and personal care products (PPCPs) in many fields has brought convenience to human lives but has also caused unavoidable environmental pollution issues. In particular, the resistance gene problem resulting from accumulating antibiotics that cannot be fully absorbed by biological individuals has been a concern; thus, it is urgent to find efficient technologies to boost the degradation efficiency of antibiotics in the environment. Here, an ε-MnO2 catalyst was prepared by a novel droplet-interface-drying method and utilized as a Fenton-like catalyst for efficiently degrading ciprofloxacin (CIP). The ε-MnO2 shell was formed preferentially at the gas–liquid interface and then continued to decompose into ε-MnO2 with abundant O vacancies in the air-insulated microcavity. The XPS result confirms that this particular preparation method can regulate the content of O vacancies in the material. Compared with ε-MnO2 samples obtained by the direct drying method (ε-MnO2-B), the catalytic performance of ε-MnO2 prepared by the droplet-interface-drying method (ε-MnO2-P) is significantly improved. By activating peroxymonosulfate (PMS) with the ε-MnO2-P catalyst, the CIP degradation efficiency can reach 84.1%. The detection and analysis of reactive oxygen species (ROS) in the ε-MnO2-P/PMS oxidation system confirms that ·OH, SO4·− and 1O2 are the main ROS for CIP degradation. This study highlights the creation of miniature hypoxic space to regulate the content of O vacancies in ε-MnO2, providing a new idea for the synthesis of other O-vacancy-rich materials. Full article
(This article belongs to the Section Inorganic Crystalline Materials)
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10 pages, 2827 KiB  
Article
Wafer-Scale Emission Energy Modulation of Indium Flushed Quantum Dots
by Nikolai Spitzer, Nikolai Bart, Hans-Georg Babin, Marcel Schmidt, Andreas D. Wieck and Arne Ludwig
Crystals 2023, 13(12), 1657; https://doi.org/10.3390/cryst13121657 - 30 Nov 2023
Cited by 1 | Viewed by 1433
Abstract
Semiconductor self-assembled quantum dots (QDs) have garnered immense attention for their potential in various quantum technologies and photonics applications. Here, we explore a novel approach for fine-tuning the emission wavelength of QDs by building upon the indium flush growth method: Submonolayer variations in [...] Read more.
Semiconductor self-assembled quantum dots (QDs) have garnered immense attention for their potential in various quantum technologies and photonics applications. Here, we explore a novel approach for fine-tuning the emission wavelength of QDs by building upon the indium flush growth method: Submonolayer variations in the capping thickness reveal a non-monotonic progression, where the emission energy can decrease even though the capping thickness decreases. indium flush, a well-known technique for inducing blue shifts in quantum dot emissions, involves the partial capping of QDs with GaAs followed by a temperature ramp-up. However, our findings reveal that the capping layer roughness, stemming from fractional monolayers during overgrowth, plays a pivotal role in modulating the emission energy of these QDs. We propose increased indium interdiffusion between the QDs and the surrounding GaAs capping layer for a rough surface surrounding the QD as the driving mechanism. This interdiffusion alters the indium content within the QDs, resulting in an additional emission energy shift, counterintuitive to the capping layer’s thickness increase. We utilize photoluminescence spectroscopy to generate wafer maps depicting the emission spectrum of the QDs. Using thickness gradients, we produce systematic variations in the capping layer thickness on 3″ wafers, resulting in modulations of the emission energy of up to 26 meV. Full article
(This article belongs to the Special Issue Modelling of Crystal Growth Processes)
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11 pages, 3200 KiB  
Article
In Situ Growth of Mg-Fe Layered Double Hydroxides (LDH) Film on Titanium Dental Implant Substrates for pH Regulation in Oral Environments
by Yuliu Li, Francesco Gianfreda, Carlotta Danesi, Patrizio Bollero, Anita Ermini, Roberto Pizzoferrato and Eleonora Nicolai
Crystals 2023, 13(12), 1636; https://doi.org/10.3390/cryst13121636 - 26 Nov 2023
Cited by 1 | Viewed by 1605
Abstract
Layered double hydroxides (LDHs) consist of two-dimensional, positively charged lamellar structures with the ability to host various anions in the interlayer spaces, which grants them unique properties and tunable characteristics. LDHs, a class of versatile inorganic compounds, have recently emerged as promising candidates [...] Read more.
Layered double hydroxides (LDHs) consist of two-dimensional, positively charged lamellar structures with the ability to host various anions in the interlayer spaces, which grants them unique properties and tunable characteristics. LDHs, a class of versatile inorganic compounds, have recently emerged as promising candidates for enhancing osseointegration. A suitable alkaline microenvironment is thought to be beneficial for stimulating osteoblasts’ differentiation (responsible for bone matrix formation) while suppressing osteoclast generation (responsible for bone matrix disintegration). LDHs are prone to adjusting their alkalinity and thus offering us the chance to study how pH affects cellular behavior. LDHs can indeed modulate the local pH, inflammatory responses, and oxidative stress levels, factors that profoundly influence the behavior of osteogenic cells and their interactions with the implant surface. Herein, we deposited Mg–Fe LDH films on titanium substrates for dental implants. The modified Ti substrates was more alkaline in comparison to the bare ones, with a pH higher than 8 after hydrolysis in an aqueous environment. Full article
(This article belongs to the Special Issue Advanced Surface Engineering Materials: Characterization and Properties)
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13 pages, 3248 KiB  
Article
NiO/Ga2O3 Vertical Rectifiers of 7 kV and 1 mm2 with 5.5 A Forward Conduction Current
by Jian-Sian Li, Hsiao-Hsuan Wan, Chao-Ching Chiang, Timothy Jinsoo Yoo, Fan Ren, Honggyu Kim and Stephen J. Pearton
Crystals 2023, 13(12), 1624; https://doi.org/10.3390/cryst13121624 - 23 Nov 2023
Cited by 6 | Viewed by 2191
Abstract
In this study, we present the fabrication and characterization of vertically oriented NiO/β polymorph n-Ga2O3/n+ Ga2O3 heterojunction rectifiers featuring a substantial area of 1 mm2. A dual-layer SiNX/SiO2 dielectric field plate [...] Read more.
In this study, we present the fabrication and characterization of vertically oriented NiO/β polymorph n-Ga2O3/n+ Ga2O3 heterojunction rectifiers featuring a substantial area of 1 mm2. A dual-layer SiNX/SiO2 dielectric field plate edge termination was employed to increase the breakdown voltage (VB). These heterojunction rectifiers exhibit remarkable simultaneous achievement of high breakdown voltage and substantial conducting currents. In particular, the devices manifest VB of 7 kV when employing a 15 µm thick drift layer doping concentration of 8.8 × 1015 cm−3, concurrently demonstrating a forward current of 5.5 A. The thick drift layer is crucial in obtaining high VB since similar devices fabricated on 10 µm thick epilayers had breakdown voltages in the range of 3.6–4.0 kV. Reference devices fabricated on the 15 µm drift layers had VB of 5 kV. The breakdown is still due to leakage current from tunneling and thermionic emission and not from avalanche breakdown. An evaluation of the power figure-of-merit, represented by VB2/RON, reveals a value of 9.2 GW·cm−2, where RON denotes the on-state resistance, measuring 5.4 mΩ·cm2. The Coff was 4 nF/cm2, leading to an RON × Coff of 34 ps and FCO of 29 GHz. The turn-on voltage for these rectifiers was ~2 V. This exceptional performance surpasses the theoretical unipolar one-dimensional (1D) limit of both SiC and GaN, underscoring the potential of β-Ga2O3 for forthcoming generations of high-power rectification devices. Full article
(This article belongs to the Special Issue Wide-Bandgap Semiconductor Materials, Devices and Systems)
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28 pages, 5270 KiB  
Review
Liquid Crystals for Luminescent Concentrators: A Review
by Atchutananda Surampudi, Guanxiong Zhang, Ravinder Singh, Grahame Faulkner, Dominic C. O’Brien, Martin J. Booth and Stephen M. Morris
Crystals 2023, 13(12), 1615; https://doi.org/10.3390/cryst13121615 - 22 Nov 2023
Cited by 6 | Viewed by 2808
Abstract
Luminescent optical concentrators are thin films containing fluorescent dyes that enable light collection over a wide field of view without the need to track the path of the Sun. However, a disadvantage when using luminescent concentrators is that the performance is often impeded [...] Read more.
Luminescent optical concentrators are thin films containing fluorescent dyes that enable light collection over a wide field of view without the need to track the path of the Sun. However, a disadvantage when using luminescent concentrators is that the performance is often impeded by surface losses through these films. Liquid-crystal (LC) hosts are attractive for luminescent concentrators, as they impart, at the very least, an orientational ordering to the transition dipole moment of the dyes dispersed within these films. This enables the directivity of both the absorption and emission and can reduce surface losses by, for example, adopting the homeotropic alignment of the LC director. This article reviews the developments and applications of LCs to luminescent optical concentrators and describes the strategies that have been introduced to further combat losses by decoupling the absorption and emission processes through Förster energy transfer, the approaches employed to enhance the chemical structures of the dyes, and the methods of using alternative LC phases and external configurations. The review presents a comprehensive summary of the material combinations and the techniques that have been considered in the development of LC-based concentrator films and concludes with a discussion about the future perspectives for these exciting optical concentrators. Full article
(This article belongs to the Special Issue Reviews in Liquid Crystals)
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15 pages, 18962 KiB  
Article
Wetting of Graphite and Platinum Substrate by Oxide System with Graded B2O3 Content
by Dalibor Novák, Lenka Řeháčková, Vlastimil Novák, Dalibor Matýsek and Pavlína Peikertová
Crystals 2023, 13(12), 1618; https://doi.org/10.3390/cryst13121618 - 22 Nov 2023
Cited by 2 | Viewed by 1271
Abstract
This work focuses on wetting two types of substrates (a platinum substrate and a polished graphite substrate) by molten polycomponent oxide system CaO–MgO–SiO2–Al2O3–B2O3 to test the level of interaction at high temperatures. The tested [...] Read more.
This work focuses on wetting two types of substrates (a platinum substrate and a polished graphite substrate) by molten polycomponent oxide system CaO–MgO–SiO2–Al2O3–B2O3 to test the level of interaction at high temperatures. The tested systems were subjected to high-temperature wetting tests in the temperature range from liquidus temperature to 1550 °C using the sessile drop method. A total of four oxide systems were tested with graded boron oxide contents ranging from 0 to 30 wt%. The experiments were conducted in a CLASIC high-temperature resistance observation furnace and an inert atmosphere of high-purity argon. Droplet silhouettes were obtained with a CANON EOS 550D high-resolution camera during heat treatment, with reactive and non-reactive wetting occurring depending on the substrate type. The dependence of the average wetting angles on temperature and time was evaluated, and it was found that boron oxide decreased the average wetting angles of molten oxide droplets. The analyses were accompanied by the SEM/EDX analysis of the substrate and FTIR analysis of the droplets after high-temperature experiments. The phase composition of the oxide systems was evaluated by XRD analysis. Full article
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11 pages, 1753 KiB  
Article
Optimization of a LaNiO3 Bottom Electrode for Flexible Pb(Zr,Ti)O3 Film-Based Ferroelectric Random Access Memory Applications
by Yeong Uk Choi, Hyun Soo Ahn, Jung Ehy Hong, Dong In Yang, Hwa-Pyeong Lee, Dae-Yong Jeong, Minbaek Lee, Jong Hun Kim and Jong Hoon Jung
Crystals 2023, 13(12), 1613; https://doi.org/10.3390/cryst13121613 - 21 Nov 2023
Cited by 1 | Viewed by 2055
Abstract
The direct growth of ferroelectric films onto flexible substrates has garnered significant interest in the advancement of portable and wearable electronic devices. However, the search for an optimized bottom electrode that can provide a large and stable remnant polarization is still ongoing. In [...] Read more.
The direct growth of ferroelectric films onto flexible substrates has garnered significant interest in the advancement of portable and wearable electronic devices. However, the search for an optimized bottom electrode that can provide a large and stable remnant polarization is still ongoing. In this study, we report the optimization of an oxide-based LaNiO3 (LNO) electrode for high-quality Pb(Zr0.52Ti0.48)O3 (PZT) thick films. The surface morphology and electrical conductivity of sol-gel-grown LNO films on a fluorophlogopite mica (F-mica) substrate were optimized at a crystallization temperature of 800 °C and a film thickness of 120 nm. Our approach represents the promising potential pairing between PZT and LNO electrodes. While LNO-coated F-mica maintains stable electrical conductivity during 1.0%-strain and 104-bending cycles, the upper PZT films exhibit a nearly square-like polarization–electric field behavior under those stress conditions. After 104 cycles at 0.5% strain, the remnant polarization shows decreases as small as ~14%. Under flat (bent) conditions, the value decreases to just 81% (49%) after 1010 fatigue cycles and to 96% (85%) after 105 s of a retention test, respectively. Full article
(This article belongs to the Special Issue Ferroelectric and Multiferroic Thin Films)
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23 pages, 9437 KiB  
Article
Additive Manufacturing and Mechanical Properties of Auxetic and Non-Auxetic Ti24Nb4Zr8Sn Biomedical Stents: A Combined Experimental and Computational Modelling Approach
by Sudipta Pramanik, Dennis Milaege, Maxwell Hein, Kay-Peter Hoyer and Mirko Schaper
Crystals 2023, 13(11), 1592; https://doi.org/10.3390/cryst13111592 - 17 Nov 2023
Cited by 2 | Viewed by 2044
Abstract
The effect of plaque deposition (atherosclerosis) on blood flow behaviour is investigated via computational fluid dynamics and structural mechanics simulations. To mitigate the narrowing of coronary artery atherosclerosis (stenosis), the computational modelling of auxetic and non-auxetic stents was performed in this study to [...] Read more.
The effect of plaque deposition (atherosclerosis) on blood flow behaviour is investigated via computational fluid dynamics and structural mechanics simulations. To mitigate the narrowing of coronary artery atherosclerosis (stenosis), the computational modelling of auxetic and non-auxetic stents was performed in this study to minimise or even avoid these deposition agents in the future. Computational modelling was performed in unrestricted (open) conditions and restricted (in an artery) conditions. Finally, stent designs were produced by additive manufacturing, and mechanical testing of the stents was undertaken. Auxetic stent 1 and auxetic stent 2 exhibit very little foreshortening and radial recoil in unrestricted deployment conditions compared to non-auxetic stent 3. However, stent 2 shows structural instability (strut failure) during unrestricted deployment conditions. For the restricted deployment condition, stent 1 shows a higher radial recoil compared to stent 3. In the tensile test simulations, short elongation for stent 1 due to strut failure is demonstrated, whereas no structural instability is noticed for stent 2 and stent 3 until 0.5 (mm/mm) strain. The as-built samples show a significant thickening of the struts of the stents resulting in short elongations during tensile testing compared to the simulations (stent 2 and stent 3). A modelling framework for the stent deployment system that enables the selection of appropriate stent designs before in vivo testing is required. This leads to the acceleration of the development process and a reduction in time, resulting in less material wastage. The modelling framework shall be useful for doctors designing patient-specific stents. Full article
(This article belongs to the Special Issue New Materials and Concepts for Additive Manufacturing with Metals II)
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18 pages, 5329 KiB  
Article
Growth, Structure, Spectroscopy, and Laser Operation of a “Mixed” Yb:(Y,Lu)3Al5O12 Garnet Crystal
by Sami Slimi, Pavel Loiko, Mingyan Pan, Pauline Lehoux, Venkatesan Jambunathan, Martin Smrz, Tomas Mocek, Yicheng Wang, Weidong Chen, Valentin Petrov, Rosa Maria Solé, Magdalena Aguiló, Francesc Díaz, Patrice Camy and Xavier Mateos
Crystals 2023, 13(11), 1588; https://doi.org/10.3390/cryst13111588 - 15 Nov 2023
Cited by 3 | Viewed by 1935
Abstract
A single crystal of ytterbium-doped “mixed” yttrium–lutetium aluminum garnet with a stoichiometric composition of (Y0.601Lu0.233Yb0.166)3Al5O12 was grown by the Czochralski method and its structure, vibronic, spectroscopic, and laser properties were studied. The [...] Read more.
A single crystal of ytterbium-doped “mixed” yttrium–lutetium aluminum garnet with a stoichiometric composition of (Y0.601Lu0.233Yb0.166)3Al5O12 was grown by the Czochralski method and its structure, vibronic, spectroscopic, and laser properties were studied. The stimulated-emission cross-section for Yb3+ ions was maximized to 2.53 × 10−20 cm2 at 1031 nm. The emission bandwidth was ~8 nm, and the reabsorption-free luminescence lifetime of the 2F5/2 state was 1.063 ms. Pumped at 941 nm, the Yb laser generated a maximum output power of 1.04 W at 1.03 and 1.05 μm with a high slope efficiency of 76.4% and a laser threshold of 76 mW. A continuous wavelength tuning over a range of 51.6 nm (1026.4–1078.0 nm) was also achieved. Power scaling was achieved using a 969 nm diode-pumped microchip cavity. A maximum output power of ~9 W was obtained at 1.05 μm with a slope efficiency of 76% and an almost circular laser beam profile. Full article
(This article belongs to the Special Issue Rare Earths-Doped Materials (3rd Edition))
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8 pages, 2227 KiB  
Article
Innovative Method for the Mass Preparation of α″-Fe16N2 Powders via Gas Atomization
by Marian Grigoras, Mihaela Lostun, Marieta Porcescu, George Stoian, Gabriel Ababei and Nicoleta Lupu
Crystals 2023, 13(11), 1578; https://doi.org/10.3390/cryst13111578 - 9 Nov 2023
Cited by 3 | Viewed by 2494
Abstract
The iron nitride materials, especially α″-Fe16N2, are considered one of the most promising candidates for future rare-earth-free magnets. However, the mass production of α″-Fe16N2 powders as a raw material for permanent magnets is still challenging. In [...] Read more.
The iron nitride materials, especially α″-Fe16N2, are considered one of the most promising candidates for future rare-earth-free magnets. However, the mass production of α″-Fe16N2 powders as a raw material for permanent magnets is still challenging. In this work, starting from iron lumps as a raw material, we have managed to prepare the α″-Fe16N2 powders via the gas atomization method, followed by subsequent nitriding in an ammonia–hydrogen gas mixture stream. The particle size was controlled by changing the gas atomization preparation conditions. X-ray diffractograms (XRD) analyses show that the prepared powders are composed of α″-Fe16N2 and α-Fe phases. The α″-Fe16N2 volume ratio increases with decreasing powder size and increasing nitriding time, reaching a maximum of 57% α″-Fe16N2 phase in powders with size below 32 ± 3 μm after 96 h nitridation. The saturation magnetization reaches the value of 237 emu/g and a reasonable coercivity value of 884 Oe. Compared to the saturation magnetization values of α-Fe powders, the α″-Fe16N2 powders prepared through our proposed approach show an increase of up to 10% in saturation and demonstrate the possibility of mass production of α″-Fe16N2 powders as precursors of permanent magnets without rare earths. Full article
(This article belongs to the Special Issue Exploring the Magnetic World: Advances in Synthesis, Characterization, and Revolutionary Applications of Magnetic Nanoparticles)
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16 pages, 5574 KiB  
Article
Single-Crystal Structure Analysis of Three Novel Iron(II) Coordination Polymers with Bridging 1,3,5-Tris((1H-1,2,4-triazol-1-yl)methyl)benzene
by Aysenur Limon, Dustin N. Jordan, Till Strothmann, Laure P. Cuignet, Yann Garcia and Christoph Janiak
Crystals 2023, 13(11), 1574; https://doi.org/10.3390/cryst13111574 - 7 Nov 2023
Viewed by 2193
Abstract
Three novel iron(II) coordination polymers, namely [Fe(H2O)2(ttmb)2](ClO4)2·4H2O (1), [Fe(H2O)2(ttmb)2](BF4)2·4H2O (2) and [Fe(NCS)2(ttmb)2 [...] Read more.
Three novel iron(II) coordination polymers, namely [Fe(H2O)2(ttmb)2](ClO4)2·4H2O (1), [Fe(H2O)2(ttmb)2](BF4)2·4H2O (2) and [Fe(NCS)2(ttmb)2] (3), were synthesized with the linker 1,3,5-tris((1H-1,2,4-triazol-1-yl)methyl)benzene (ttmb). The single-crystal structures show that all three compounds form a double-chain structure with the adjacent iron atoms being bridged by two ttmb linkers. The iron(II) ions are octahedrally surrounded by four N4 donor atoms from the 1,2,4-triazol-1-yl groups of four different ttmb linkers which form an equatorial plane and two trans-coordinated aqua ligands in 1 and 2 or isothiocyanato ligands in 3 in the axial positions. In view of the neutral bridging ttmb linker, there is a non-coordinated counter-anion in 1 and 2 (ClO4 and BF4, respectively), and a coordinated NCS anion in 3. Compounds 1 and 2 are isostructural. Interestingly, the ttmb linker only utilizes two of its three potentially coordinating triazole groups. All iron(II) coordination networks are colorless or have a light-yellow color, being indicative of the high-spin state. Full article
(This article belongs to the Special Issue Coordination Complexes: Synthesis, Characterization and Application)
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13 pages, 2168 KiB  
Article
Unveiling the Magnetic and Structural Properties of (X2YZ; X = Co and Ni, Y = Fe and Mn, and Z = Si) Full-Heusler Alloy Microwires with Fixed Geometrical Parameters
by Mohamed Salaheldeen, Valentina Zhukova, Mihail Ipatov and Arcady Zhukov
Crystals 2023, 13(11), 1550; https://doi.org/10.3390/cryst13111550 - 29 Oct 2023
Cited by 7 | Viewed by 1489
Abstract
We studied Ni2FeSi-, Co2FeSi-, and Co2MnSi-based full-Heusler alloy glass-coated microwires with the same geometric parameters, i.e., fixed nucleus and total diameters, prepared using the Taylor–Ulitovsky method. The fabrication of X2YZ (X = Co and Ni, [...] Read more.
We studied Ni2FeSi-, Co2FeSi-, and Co2MnSi-based full-Heusler alloy glass-coated microwires with the same geometric parameters, i.e., fixed nucleus and total diameters, prepared using the Taylor–Ulitovsky method. The fabrication of X2YZ (X = Co and Ni, Y = Fe and Mn, and Z = Si)-based glass-coated microwires with fixed geometric parameters is quite challenging due to the different sample preparation conditions. The XRD analysis showed a nanocrystalline microstructure for all the samples. The space groups Fm3¯m (FCC) and Im3¯m (BCC) with disordered B2 and A2 types are observed for Ni2FeSi and Co2FeSi, respectively. Meanwhile, a well-defined, ordered L21 type was observed for Co2MnSi GCMWs. The change in the positions of Ni, Co and Mn, Fe in X2YSi resulted in a variation in the lattice cell parameters and average grain size of the sample. The room-temperature magnetic behavior showed a dramatic change depending on the chemical composition, where Ni2FeSi MWs showed the highest coercivity (Hc) compared to Co2FeSi and Co2MnSi MWs. The Hc value of Ni2FeSi MWs was 16 times higher than that of Co2MnSi MWs and 3 times higher than that of Co2FeSi MWs. Meanwhile, the highest reduced remanence was reported for Co2FeSi MWs (Mr = 0.92), being about 0.82 and 0.22 for Ni2FeSi and Co2MnSi MWs, respectively. From the analysis of the temperature dependence of the magnetic properties (Hc and Mr) of X2YZ MWs, we deduced that the Hc showed a stable tendency for Co2MnSi and Co2FeSi MWs. Meanwhile, two flipped points were observed for Ni2FeSi MWs, where the behavior of Hc changed with temperature. For Mr, a monotonic increase on decreasing the temperature was observed for Co2FeSi and Ni2FeSi MWs, and it remained roughly stable for Co2MnSi MWs. The thermomagnetic curves at low magnetic field showed irreversible magnetic behavior for Co2MnSi and Co2FeSi MWs and regular ferromagnetic behavior for Ni2FeSi MWs. The current result illustrates the ability to tailor the structure and magnetic behavior of X2YZ MWs at fixed geometric parameters. Additionally, a different behavior was revealed in X2YZ MWs depending on the degree of ordering and element distribution. The tunability of the magnetic properties of X2YZ MWs makes them suitable for sensing applications. Full article
(This article belongs to the Topic Advanced Magnetic Alloys)
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11 pages, 984 KiB  
Article
Raman Spectroscopic Study of Ruddlesden—Popper Tetragonal Sr2VO4
by Romain Viennois, David Bourgogne and Julien Haines
Crystals 2023, 13(11), 1541; https://doi.org/10.3390/cryst13111541 - 27 Oct 2023
Cited by 2 | Viewed by 1488
Abstract
The lattice dynamics of tetragonal Sr2VO4 with a Ruddlesden—Popper-layered crystal structure was studied via Raman spectroscopy. We observed three of the four expected Raman-active modes under ambient conditions. Mode Grüneisen parameters and the implicit fractions of two A1g Raman-active [...] Read more.
The lattice dynamics of tetragonal Sr2VO4 with a Ruddlesden—Popper-layered crystal structure was studied via Raman spectroscopy. We observed three of the four expected Raman-active modes under ambient conditions. Mode Grüneisen parameters and the implicit fractions of two A1g Raman-active modes were determined from high-pressure and high-temperature Raman spectroscopy experiments. The low-energy A1g Raman-active mode involving Sr motions along the c direction has a large isothermal Grüneisen parameter about seven times larger than that of the high-energy A1g Raman-active mode involving apical O motions along the c direction and is, therefore, more anharmonic. The thermodynamic Grüneisen parameter is significantly smaller in Sr2VO4 than in Sr2TiO4 due to the smaller Grüneisen parameter of the high-energy A1g Raman-active mode and other vibrational modes that still need to be identified. The explicit contribution of the low-energy A1g Raman-active mode is negative, and the implicit contribution due to volume change is much larger. Both volume implicit and anharmonic explicit contributions of the high-energy A1g Raman-active mode have similar positive values. The Raman experiment in the air shows that Sr2VO4 begins to decompose above 200 °C. Full article
(This article belongs to the Special Issue Raman Scattering in Optical Crystals (Volume II))
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12 pages, 3460 KiB  
Article
Fixed-Target Pink-Beam Serial Synchrotron Crystallography at Pohang Light Source II
by Yongsam Kim and Ki Hyun Nam
Crystals 2023, 13(11), 1544; https://doi.org/10.3390/cryst13111544 - 27 Oct 2023
Cited by 4 | Viewed by 1741
Abstract
Serial crystallography (SX) enables the determination of the structure of macromolecules or small molecules with minimal radiation damage. In particular, biomolecule structures determined using the SX technique have the advantage of providing room-temperature crystal structures with high biological relevance. The SX technique requires [...] Read more.
Serial crystallography (SX) enables the determination of the structure of macromolecules or small molecules with minimal radiation damage. In particular, biomolecule structures determined using the SX technique have the advantage of providing room-temperature crystal structures with high biological relevance. The SX technique requires numerous crystals to be collected to complete three-dimensional structural information. To minimize crystal sample consumption, we introduced SX data collection with fixed-target (FT) pink-beam serial synchrotron crystallography (SSX) at the 1C beamline of Pohang Light Source II. A new sample holder consisting of a magnetic frame with a nylon mesh was developed for easy sample handling. The FT-pink-SSX diffraction data were collected by continuously scanning X-rays using a stepping motor. The room-temperature structures of glucose isomerase and lysozyme were successfully determined at a resolution of 1.7 and 2.2 Å, respectively. The use of pink-beam FT-SSX in experimental applications and data acquisition for large beam sizes is discussed. Our results provide useful information for future pink-beam SSX and SX data collection using large X-ray beams. Full article
(This article belongs to the Special Issue X-Ray Protein Crystallography)
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15 pages, 8814 KiB  
Article
Crystal Growth and the Structure of a New Quaternary Adamantine Cu☐GaGeS4
by Yvonne Tomm, Daniel M. Többens, Galina Gurieva and Susan Schorr
Crystals 2023, 13(11), 1545; https://doi.org/10.3390/cryst13111545 - 27 Oct 2023
Viewed by 1457
Abstract
Single crystals of quaternary adamantine-type Cu☐GaGeS4 were grown using the chemical vapor transport technique, with iodine as the transport agent. Dark red transparent crystals were grown in a temperature gradient of ΔT = 900–750 °C. Chemical characterization by X-ray fluorescence showed the [...] Read more.
Single crystals of quaternary adamantine-type Cu☐GaGeS4 were grown using the chemical vapor transport technique, with iodine as the transport agent. Dark red transparent crystals were grown in a temperature gradient of ΔT = 900–750 °C. Chemical characterization by X-ray fluorescence showed the off-stoichiometric composition of Cu☐GaGeS4 crystals—in particular, a slight Ge deficiency was observed. By X-ray diffraction, Cu☐GaGeS4 was found to adopt the chalcopyrite-type structure with the space group I4¯2d. Cation distribution in this structure was analyzed by multiple energy anomalous synchrotron X-ray diffraction, and it was found that Cu and vacancies occupied the 4a site, whereas Ga and Ge occupied the 4b site. The band gap energies of several off-stoichiometric Cu☐GaGeS4 crystals were determined by UV-Vis spectroscopy and ranged from 2.1 to 2.4 eV. A non-linear correlation of the band gap energy with the Ge content of the compound was shown to follow the usual bowing behavior of semiconductor alloys, with a bowing parameter of b = −1.45 (0.08). Full article
(This article belongs to the Section Materials for Energy Applications)
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12 pages, 1856 KiB  
Review
Nitride Wide-Bandgap Semiconductors for UV Nonlinear Optics
by Shihang Li and Lei Kang
Crystals 2023, 13(11), 1536; https://doi.org/10.3390/cryst13111536 - 26 Oct 2023
Cited by 1 | Viewed by 1875
Abstract
Nitride wide-bandgap semiconductors possess a wide tunable energy bandgap and abundant coordination anionic groups. This suggests their potential to display nonlinear optical (NLO) properties in the UV wavelength spectrum. This paper reports recent progress and material discoveries in exploring UV NLO structures using [...] Read more.
Nitride wide-bandgap semiconductors possess a wide tunable energy bandgap and abundant coordination anionic groups. This suggests their potential to display nonlinear optical (NLO) properties in the UV wavelength spectrum. This paper reports recent progress and material discoveries in exploring UV NLO structures using nitrides. The study emphasizes their underlying structure–property correlations in order to provide a summary of the potential performance and application value of important nitride NLO crystals. Additionally, the text underscores the benefits of nitrides in terms of optical transparency, second-harmonic-generation effects, and the birefringent phase matching output wavelength limits, while addressing current issues in terms of theoretical outlook and experimental exploration. Full article
(This article belongs to the Special Issue Advances of Nonlinear Optical Materials)
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15 pages, 2426 KiB  
Article
EXtra-Xwiz: A Tool to Streamline Serial Femtosecond Crystallography Workflows at European XFEL
by Oleksii Turkot, Fabio Dall’Antonia, Richard J. Bean, Juncheng E, Hans Fangohr, Danilo E. Ferreira de Lima, Sravya Kantamneni, Henry J. Kirkwood, Faisal H. M. Koua, Adrian P. Mancuso, Diogo V. M. Melo, Adam Round, Michael Schuh, Egor Sobolev, Raphaël de Wijn, James J. Wrigley and Luca Gelisio
Crystals 2023, 13(11), 1533; https://doi.org/10.3390/cryst13111533 - 24 Oct 2023
Cited by 3 | Viewed by 2023
Abstract
X-ray free electron lasers deliver photon pulses that are bright enough to observe diffraction from extremely small crystals at a time scale that outruns their destruction. As crystals are continuously replaced, this technique is termed serial femtosecond crystallography (SFX). Due to its high [...] Read more.
X-ray free electron lasers deliver photon pulses that are bright enough to observe diffraction from extremely small crystals at a time scale that outruns their destruction. As crystals are continuously replaced, this technique is termed serial femtosecond crystallography (SFX). Due to its high pulse repetition rate, the European XFEL enables the collection of rich and extensive data sets, which are suited to study various scientific problems, including ultra-fast processes. The enormous data rate, data complexity, and the nature of the pixelized multimodular area detectors at the European XFEL pose severe challenges to users. To streamline the analysis of the SFX data, we developed the semiautomated pipeline EXtra-Xwiz around the established CrystFEL program suite, thereby processing diffraction patterns on detector frames into structure factors. Here we present EXtra-Xwiz, and we introduce its architecture and use by means of a tutorial. Future plans for its development and expansion are also discussed. Full article
(This article belongs to the Special Issue Diffractive Imaging of Crystalline Materials at XFELs and Synchrotrons)
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9 pages, 3772 KiB  
Article
Spin-Polarized 2D Electron Gas at the EuTiO3/EuO Interface
by Jonathan Gjerde, Mahmoud Hammouri and Radi A. Jishi
Crystals 2023, 13(10), 1511; https://doi.org/10.3390/cryst13101511 - 18 Oct 2023
Viewed by 1509
Abstract
Perovskite oxide heterostructures have provided opportunities for new technologies and materials with novel properties.In particular, researchers have been interested in the magnetism and two-dimensional electron gases that form at the interface of many of these heterostructures. Often, these properties are due to polar [...] Read more.
Perovskite oxide heterostructures have provided opportunities for new technologies and materials with novel properties.In particular, researchers have been interested in the magnetism and two-dimensional electron gases that form at the interface of many of these heterostructures. Often, these properties are due to polar discontinuities, but here we use first-principles calculations to examine a heterostructure whose elements, EuO and EuTiO3, are both non-polar, yet are still conductive due to oxygen vacancies. Furthermore, the free electrons at the interface of this heterostructure are predicted to be spin-polarized, opening up possibilities for future research and devices. Full article
(This article belongs to the Section Materials for Energy Applications)
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11 pages, 3330 KiB  
Article
Ultrahigh-Density Superhard Hexagonal BN and SiC with Quartz Topology from Crystal Chemistry and First Principles
by Samir F. Matar and Vladimir L. Solozhenko
Crystals 2023, 13(10), 1498; https://doi.org/10.3390/cryst13101498 - 14 Oct 2023
Cited by 3 | Viewed by 1506
Abstract
Based on superdense C6 with a quartz (qtz) topology, new ultrahigh-density hexagonal binary phases, qtz BN and qtz SiC, were identified via full geometry structure relaxations and ground state energies using calculations based on the quantum density functional theory (DFT) [...] Read more.
Based on superdense C6 with a quartz (qtz) topology, new ultrahigh-density hexagonal binary phases, qtz BN and qtz SiC, were identified via full geometry structure relaxations and ground state energies using calculations based on the quantum density functional theory (DFT) with a gradient GGA exchange–correlation XC functional. Like qtz C6, with respect to diamond, the resulting binary qtz BN and qtz SiC were found to be less cohesive than cubic BN and cubic SiC, respectively, but were confirmed to be mechanically (elastic constants) and dynamically (phonon band structures) stable. Higher densities of the new phases correlate with higher hardness values compared to cubic BN and cubic SiC. In contrast to the regular tetrahedra that characterize the cubic BN and SiC phases, the corner-sharing tetrahedra in the new phases are distorted, which accounts for their exceptional density and hardness. All three qtz phases were found to be semiconducting to insulators, with reduced band gaps compared to diamond, cubic BN, and cubic SiC. Full article
(This article belongs to the Special Issue First Principles Calculation for Crystalline Materials)
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11 pages, 6967 KiB  
Article
Side-Chain Labeling Strategy for Forming Self-Sorted Columnar Liquid Crystals from Binary Discotic Systems
by Tsuneaki Sakurai, Kenichi Kato and Masaki Shimizu
Crystals 2023, 13(10), 1473; https://doi.org/10.3390/cryst13101473 - 10 Oct 2023
Cited by 1 | Viewed by 2107
Abstract
The spontaneous formation of self-sorted columnar structures of electron-donating and accepting π-conjugated molecules is attractive for photoconducting and photovoltaic properties. However, the simple mixing of donor–acceptor discotic molecules usually results in the formation of mixed-stacked or alternating-stacked columns. As a new strategy for [...] Read more.
The spontaneous formation of self-sorted columnar structures of electron-donating and accepting π-conjugated molecules is attractive for photoconducting and photovoltaic properties. However, the simple mixing of donor–acceptor discotic molecules usually results in the formation of mixed-stacked or alternating-stacked columns. As a new strategy for overcoming this problem, here, we report the “side-chain labeling” approach using binary discotic systems and realize the preferential formation of such self-sorted columnar structures in a thermodynamically stable phase. The demonstrated key strategy involves the use of hydrophobic and hydrophilic side chains. The prepared blend is composed of liquid crystalline phthalocyanine with branched alkyl chains (H2Pc) and perylenediimide (PDI) carrying alkyl chains at one side and triethyleneglycol (TEG) chains at the other side (PDIC12/TEG). To avoid the thermodynamically unfavorable contact among hydrophobic and hydrophilic chains, PDIC12/TEG self-assembles to stack up on top of each other and H2Pc as well, forming a homo-stacked pair of columns (self-sort). Importantly, H2Pc and PDIC12/TEG in the blend are macroscopically miscible and uniform, and mesoscopically segregated. The columnar liquid crystalline microdomains of H2Pc and PDIC12/TEG are homeotropically aligned in a glass sandwiched cell. The “labeling” strategy demonstrated here is potentially applicable to any binary discotic system and enables the preferential formation of self-sorted columnar structures. Full article
(This article belongs to the Special Issue State-of-the-Art Liquid Crystals Research in Japan)
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14 pages, 3462 KiB  
Article
Off-Eutectic Growth Model for Solidifying Alloy from an Undercooled State
by Junfeng Xu and Peter K. Galenko
Crystals 2023, 13(10), 1453; https://doi.org/10.3390/cryst13101453 - 29 Sep 2023
Viewed by 1491
Abstract
Classical eutectic growth models are based on the use of eutectic composition. These models neglect the effect of primary phase formation, and their direct use in the rapid solidification process of off-eutectic (hypoeutectic and hypereutectic) alloys is absent. Combining the effect of the [...] Read more.
Classical eutectic growth models are based on the use of eutectic composition. These models neglect the effect of primary phase formation, and their direct use in the rapid solidification process of off-eutectic (hypoeutectic and hypereutectic) alloys is absent. Combining the effect of the primary phase in the eutectic transformation and an off-eutectic composition, the solidification growth model is derived in the present work. The effect of the model and material parameters on solidification kinetics is discussed in comparison with experimental data. Computational results on the off-eutectic growth model show that the model agrees well with experimental data on the solidification kinetics of Ni–B and Ti–Si alloys. Full article
(This article belongs to the Special Issue Phase Transition in External Fields (2nd Edition))
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11 pages, 4133 KiB  
Article
Flux Growth and Characterization of Bulk InVO4 Crystals
by Olesia Voloshyna, Mikhail V. Gorbunov, Daria Mikhailova, Andrey Maljuk, Silvia Seiro and Bernd Büchner
Crystals 2023, 13(10), 1439; https://doi.org/10.3390/cryst13101439 - 28 Sep 2023
Cited by 1 | Viewed by 1537
Abstract
The flux growth of InVO4 bulk single crystals has been explored for the first time. The reported eutectic composition at a ratio of V2O5:InVO4 = 1:1 could not be used as a self-flux since no sign of [...] Read more.
The flux growth of InVO4 bulk single crystals has been explored for the first time. The reported eutectic composition at a ratio of V2O5:InVO4 = 1:1 could not be used as a self-flux since no sign of melting was observed up to 1100 °C. Crystals of InVO4 of typical size 0.5 × 1 × 7 mm3 were obtained using copper pyrovanadate (Cu2V2O7) as a flux, using Pt crucibles. X-ray powder diffraction confirmed the orthorhombic Cmcm structure. Rests of the flux material were observed on the sample surface, with occasional traces of Pt indicating some level of reaction with the crucible. X-ray absorption spectroscopy showed that oxidation states of indium and vanadium ions are +3 and +5, respectively. The size and high quality of the obtained InVO4 crystals makes them excellent candidates for further study of their physical properties. Full article
(This article belongs to the Special Issue Application of X-ray and Electron to Crystal Structure Characterization)
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13 pages, 6489 KiB  
Article
Room-Temperature, Nanoscale Multiferroic Pb(Fe0.5Ta0.5)1−x(Zr0.53Ti0.47)xO3 (x = 0.2, 0.3) Thin Films Grown via the Pulsed Laser Deposition Technique
by Dilsom A. Sanchez, Karuna Kara Mishra, Sujoy Saha, Gopalan Srinivasan and Ram S. Katiyar
Crystals 2023, 13(10), 1442; https://doi.org/10.3390/cryst13101442 - 28 Sep 2023
Viewed by 1746
Abstract
Multiferroic materials capable of robust magnetoelectric coupling at room temperature are currently being explored for their possible multifunctional device applications. Highly (100)-oriented Pb(Fe0.5Ta0.5)x(Zr0.53Ti0.47)1−x (PZTFTx) thin films (x = 0.2 and [...] Read more.
Multiferroic materials capable of robust magnetoelectric coupling at room temperature are currently being explored for their possible multifunctional device applications. Highly (100)-oriented Pb(Fe0.5Ta0.5)x(Zr0.53Ti0.47)1−x (PZTFTx) thin films (x = 0.2 and 0.3) with a thickness of about 300 nm were grown on La0.67Sr0.33CoO3 (LSCO)-buffered MgO 100-oriented substrates via the pulsed laser deposition method. An analysis of their X-ray diffraction patterns suggests the stabilization of the orthorhombic phase in the thin films at room temperature. Dielectric spectroscopic measurements of the metal–insulator–metal (Pt/PZTFTx/LSCO) thin-film capacitors as a function of temperature revealed a diffuse ferroelectric-to-paraelectric phase transition around Tm ~520 and 560 K for the x = 0.2 and 0.3 thin films, respectively. Well-saturated electrical hysteresis loops with large remanent (Pr) and saturation (Ps) polarizations were observed in these capacitors, which indicates the establishment of intrinsic ferroelectric ordering in the thin films at room temperature. These thin films retained ferromagnetic/ferrimagnetic ordering up to 300 K and showed saturation magnetization values of 8.3 (x = 0.2) and 6.1 (x = 0.3) emu/cm3 at room temperature. The magnetoelectric coupling constants of 2040 mV/cmOe (x = 0.2) and 850 mV/cmOe (x = 0.3), respectively, were obtained at an in-plane bias field at room temperature. The present study demonstrates that PZTFTx thin films are multiferroic at room temperature with large magnetoelectric couplings, and these materials may be suitable for use in magnetic sensors and spintronic device applications. Full article
(This article belongs to the Special Issue Research Progress of Perovskite Ferroelectric Materials)
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18 pages, 4236 KiB  
Article
A Coupled Approach to Compute the Dislocation Density Development during Czochralski Growth and Its Application to the Growth of High-Purity Germanium (HPGe)
by Wolfram Miller, Andrejs Sabanskis, Alexander Gybin, Kevin-P. Gradwohl, Arved Wintzer, Kaspars Dadzis, Jānis Virbulis and Radhakrishnan Sumathi
Crystals 2023, 13(10), 1440; https://doi.org/10.3390/cryst13101440 - 28 Sep 2023
Cited by 3 | Viewed by 1620
Abstract
The evolution of the dislocation density during Czochralski growth is computed by the combination of global thermal calculations and local computation of the stress and dislocation density in the crystal. The global simulation was performed using the open-source software Elmer (version 8.4) and [...] Read more.
The evolution of the dislocation density during Czochralski growth is computed by the combination of global thermal calculations and local computation of the stress and dislocation density in the crystal. The global simulation was performed using the open-source software Elmer (version 8.4) and the local simulation with the open-source software MACPLAS (version of 23.1.2023). Interpolation both in space and time was used to transfer the boundary conditions from the global simulations to the local model, which uses a different mesh discretization and a considerably smaller time step. We applied this approach to the Czochralski growth of a high-purity Ge crystal. The heater power change predicted by the global model as well as the final dislocation density distribution in the crystal simulated by the local model are correlated to the experimental results. Full article
(This article belongs to the Special Issue Advances in Crystal Growth: Pioneering Materials for Tomorrow's Technologies)
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