Crystals

38 pages, 10149 KiB

Open AccessEditor’s ChoiceReview

Crystallization of Polymers with a Reduced Density of Entanglements

by Andrzej Pawlak

Crystals 2024, 14(4), 385; https://doi.org/10.3390/cryst14040385 - 20 Apr 2024

Cited by 1 | Viewed by 1388

Since methods for reducing macromolecule entanglements have been developed, it has become possible to better understand the impact of polymer chain entanglement on the crystallization process. The article presents basic information about the disentangling of macromolecules and the characterization of the degree of [...] Read more.

Since methods for reducing macromolecule entanglements have been developed, it has become possible to better understand the impact of polymer chain entanglement on the crystallization process. The article presents basic information about the disentangling of macromolecules and the characterization of the degree of entanglement. The basic knowledge of polymer crystallization was also presented. Then, it was discussed how polymers crystallize during their disentangling. Non-isothermal and isothermal crystallization experiments using disentangled polymers, and for comparison using entangled polymers, are described in more detail. The influence of disentangling on both nucleation and crystal growth is highlighted. It is also shown how the crystallization of polymers changes when macromolecules re-entangle. Full article

(This article belongs to the Section Macromolecular Crystals)

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14 pages, 18119 KiB

Open AccessEditor’s ChoiceArticle

Novel Tetragonal Boron Pnictides BX (X = N, P, As, Sb, Bi) with Square B2X2 Motifs from Crystal Chemistry and First Principles

by Samir F. Matar and Vladimir L. Solozhenko

Crystals 2024, 14(4), 359; https://doi.org/10.3390/cryst14040359 - 11 Apr 2024

Viewed by 977

Abstract

Novel tetragonal (P4₂/mnm) boron pnictides BX (X = N, P, As, Sb, Bi) with chromium boride (crb) topology exhibiting a square B2X2 motif with resulting edge- and corner-sharing tetrahedra were predicted from crystal chemistry and [...] Read more.

Novel tetragonal (P4₂/mnm) boron pnictides BX (X = N, P, As, Sb, Bi) with chromium boride (crb) topology exhibiting a square B2X2 motif with resulting edge- and corner-sharing tetrahedra were predicted from crystal chemistry and extensively characterized by density functional theory (DFT) calculations. All new BX phases were found to be cohesive with decreasing cohesive energy along the series. Mechanically stable with positive sets of elastic constants, all crb phases exhibit slightly lower hardness than other BX polymorphs due to increased openness of the crystal structures. All-positive phonon frequencies characterize the crb BX family except for X = Bi, which shows a slight acoustic instability; also, the shape of the phonon spectra changes from band-like for X = N, P, As to flat bands for the heavier elements. The electronic band structures reveal insulating to semiconducting properties for crb BX, depending on the pnictogen nature along the series. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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21 pages, 8810 KiB

Open AccessEditor’s ChoiceArticle

Synthesis and Crystal Structures of Two Crystalline Silicic Acids: Hydrated H-Apophyllite, H₁₆Si₁₆O₄₀ • 8–10 H₂O and H-Carletonite, H₃₂Si₆₄O₁₄₄

by Bernd Marler and Isabel Grosskreuz

Crystals 2024, 14(4), 326; https://doi.org/10.3390/cryst14040326 - 30 Mar 2024

Viewed by 850

Abstract

Hydrated H-Apophyllite (HH-Apo) and H-carletonite (H-Car) were synthesized at 0 °C by leaching an apophyllite and a carletonite single crystal in a large surplus of 1.2 molar hydrochloric acid. The XRD powder patterns of HH-Apo and H-Car were indexed with space group symmetries [...] Read more.

Hydrated H-Apophyllite (HH-Apo) and H-carletonite (H-Car) were synthesized at 0 °C by leaching an apophyllite and a carletonite single crystal in a large surplus of 1.2 molar hydrochloric acid. The XRD powder patterns of HH-Apo and H-Car were indexed with space group symmetries of P4/ncc and I4/mcm and lattice parameters of a = 8.4872(2) Å, c = 16.8684(8) Å and a = 13.8972(3) Å, c = 20.4677(21) Å, respectively. The crystal structures were solved based on model building of the structures of the precursors and a physico-chemical characterization. Rietveld structure refinements confirmed the structure models. HH-Apo and H-Car are among the very few crystalline silicic acids whose structures have been determined and confirmed based on a structure refinement. The structure of HH-Apo contains thin silicate monolayers that can be regarded as constructed by rings of interconnected [SiO₃OH] tetrahedra which form a puckered silicate layer. A sheet of water molecules is intercalated between the silicate layers. There are no direct hydrogen bonds between the silanol groups, but there are hydrogen bonds of different strengths between the terminal O atoms of the silicate layers and the intercalated water molecules. The ¹H MAS NMR spectrum presents a strong signal at 4.9 ppm related to the aforementioned bonds and interactions between the water molecules, as well as a small signal at 22.5 ppm corresponding to an extremely strong hydrogen bond with d(O...O) ≈ 2.2 Å. The structure of H-Car is free of structural water and consists exclusively of microporous silicate double-layers with 4-connected [SiO₄] and 3-connected [SiO₃OH] tetrahedra in a ratio of 1:1 and a thickness of 9.2 Å. Neighboring layers are connected to each other by medium–strong hydrogen bonds with O...O distances of 2.56 Å. The structure of HH-Apo decays within several hours while H-Car is stable. A topotactic condensation reaction applied to H-Car forms an irregularly condensed silicate which still contains the layers in a distorted form as building blocks. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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20 pages, 12081 KiB

Open AccessEditor’s ChoiceArticle

Crystal Plasticity Modeling to Capture Microstructural Variations in Cold-Sprayed Materials

by Aulora Williams, YubRaj Paudel, Shiraz Mujahid, Marc Pepi, Peter Czech, Haitham El Kadiri and Hongjoo Rhee

Crystals 2024, 14(4), 329; https://doi.org/10.3390/cryst14040329 - 30 Mar 2024

Cited by 1 | Viewed by 887

Abstract

The high-velocity impact of powder particles in cold-spray additively manufactured (CSAM) parts creates intersplat boundaries with regions of high dislocation densities and sub-grain structures. Upon microstructure and mechanical characterization, CSAM Aluminum 6061 showed non-uniformity with spatial variation in the microstructure and mechanical properties, [...] Read more.

The high-velocity impact of powder particles in cold-spray additively manufactured (CSAM) parts creates intersplat boundaries with regions of high dislocation densities and sub-grain structures. Upon microstructure and mechanical characterization, CSAM Aluminum 6061 showed non-uniformity with spatial variation in the microstructure and mechanical properties, affecting the overall response of the additively manufactured parts. Post-processing treatments are conducted in as-printed samples to improve particle bonding, relieve residual stresses, and improve mechanical properties. In this work, we attempt to implement the effects of grain size and distribution of smaller grains along the intersplat boundaries using the grain size distribution function and powder size information to accurately predict the deformation response of cold-sprayed material using a mean-field viscoplastic self-consistent (VPSC) model. The incorporation of an intersplat boundary term in the VPSC model resulted in a stress–strain response closely matching the experimental findings, preventing the superficially high stresses observed due to Hall–Petch effects from ultra-fine-grain structures. Likewise, the results from the grain analysis showed the combined effects of grain size, orientation, and intersplat mechanisms that captured the stresses experienced and strain accommodated by individual grains. Full article

(This article belongs to the Special Issue Processing-Microstructure-Properties Relationship of Advanced Alloys)

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15 pages, 11726 KiB

Open AccessEditor’s ChoiceArticle

Two New Energetic Hexagonal Anti-Perovskites (N₂H₅)₃X[B₁₂H₁₂] · H₂O (X⁻ = [NO₃]⁻ and [ClO₄]⁻): Crystal Structure, Vibrational Spectra, and Thermal Decomposition

by Rouzbeh Aghaei Hakkak, Thomas M. Klapötke and Thomas Schleid

Crystals 2024, 14(4), 310; https://doi.org/10.3390/cryst14040310 - 27 Mar 2024

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Abstract

Two novel energetic anti-perovskite compounds with the chemical formula (N₂H₅)₃X[B₁₂H₁₂] · H₂O, where X⁻ is either [NO₃]⁻ or [ClO₄]⁻, were successfully [...] Read more.

Two novel energetic anti-perovskite compounds with the chemical formula (N₂H₅)₃X[B₁₂H₁₂] · H₂O, where X⁻ is either [NO₃]⁻ or [ClO₄]⁻, were successfully synthesized. Both dodecahydro-closo-dodecaborates crystallize orthorhombically in the space group Cmc2₁, exhibiting relatively similar lattice parameters ((N₂H₅)₃[NO₃][B₁₂H₁₂] · H₂O: a = 915.94(5), b = 1817.45(9), c = 952.67(5) pm, (N₂H₅)₃[ClO₄][B₁₂H₁₂] · H₂O: a = 1040.51(6), b = 1757.68(9), c = 942.34(5) pm both for Z = 4). Their synthesis involved a two-step process: first, Cs₂[B₁₂H₁₂] passed through a cation exchange column to yield the acidic form of the dodecahydro-closo-dodecaborate, (H₃O)₂[B₁₂H₁₂]. This aqueous solution was subsequently neutralized with hydrazinium hydroxide and mixed with the corresponding water-dissolved hydrazinium salt (nitrate or perchlorate). Characterization of the obtained crystals was performed by single-crystal X-ray diffraction and Raman spectroscopy as well as thermal analyses (TG-DTA and DSC). The crystal structure determinations revealed that both compounds adopt a hexagonal anti-perovskite structure, distorted by the presence of water molecules. These compounds containing oxidizing oxoanions demonstrate a remarkable ability to release large amounts of energy (almost 2100 J/g) upon thermal decomposition. Full article

(This article belongs to the Section Materials for Energy Applications)

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10 pages, 4921 KiB

Open AccessEditor’s ChoiceArticle

The Effect of Sputtering Target Density on the Crystal and Electronic Structure of Epitaxial BaTiO₃ Thin Films

by Fugang Qi, Shaoqin Peng, Jiachang Bi, Shunda Zhang, Guanhua Su, Peiyi Li, Jiahui Zhang, Tengteng Zhang, Weisong Zhou, Ruyi Zhang and Yanwei Cao

Crystals 2024, 14(4), 304; https://doi.org/10.3390/cryst14040304 - 26 Mar 2024

Viewed by 1175

Abstract

Barium titanate (BaTiO₃) is a promising material for silicon-integrated photonics due to its large electro-optical coefficients, low loss, high refractive index, and fast response speed. Several deposition methods have been employed to synthesize BaTiO₃ films. Magnetron sputtering is one of [...] Read more.

Barium titanate (BaTiO₃) is a promising material for silicon-integrated photonics due to its large electro-optical coefficients, low loss, high refractive index, and fast response speed. Several deposition methods have been employed to synthesize BaTiO₃ films. Magnetron sputtering is one of these methods, which offers specific advantages for growing large-scale films. However, there is a scarcity of studies investigating the effect of sputtering target density on the quality of BaTiO₃ films. Therefore, this study aims to uncover the effect of sputtering targets on the crystal and electronic structures of epitaxial BaTiO₃ thin films. Two BaTiO₃ ceramic targets were sintered at different densities by altering the sintering temperatures. The crystal structure and chemical composition of the targets were then characterized using X-ray diffraction, Raman spectroscopy, and scanning electron microscopy with energy-dispersive X-ray spectroscopy. Subsequently, BaTiO₃ epitaxial films were grown by magnetron sputtering using these two targets. The crystal and electronic structures of the BaTiO₃ films were analyzed using high-resolution X-ray diffraction, X-ray photoemission spectroscopy, atomic force microscopy, and spectroscopic ellipsometry. Notably, the BaTiO₃ films grown with high-density targets show superior quality but contain oxygen vacancies, whereas those films synthesized with low-density targets display high surface roughness. These findings provide insights into the effect of sputtering target density on the crystal and electronic structures of epitaxial BaTiO₃ thin films. Full article

(This article belongs to the Special Issue Epitaxial Growth and Application of Metallic Oxide Thin Films)

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26 pages, 3846 KiB

Open AccessEditor’s ChoiceReview

Nanostructured Materials for Enhanced Performance of Solid Oxide Fuel Cells: A Comprehensive Review

by Hicham Helal, Mohammadi Ahrouch, Abdelaziz Rabehi, Dario Zappa and Elisabetta Comini

Crystals 2024, 14(4), 306; https://doi.org/10.3390/cryst14040306 - 26 Mar 2024

Viewed by 1445

Abstract

Solid oxide fuel cells (SOFCs) have emerged as promising candidates for efficient and environmentally friendly energy conversion technologies. Their high energy conversion efficiency and fuel flexibility make them particularly attractive for various applications, ranging from stationary power generation to portable electronic devices. Recently, [...] Read more.

Solid oxide fuel cells (SOFCs) have emerged as promising candidates for efficient and environmentally friendly energy conversion technologies. Their high energy conversion efficiency and fuel flexibility make them particularly attractive for various applications, ranging from stationary power generation to portable electronic devices. Recently, research has focused on utilizing nanostructured materials to enhance the performance of SOFCs. This comprehensive review summarizes the latest advancements in the design, fabrication, and characterization of nanostructured materials integrated in SOFC. The review begins by elucidating the fundamental principles underlying SOFC operation, emphasizing the critical role of electrode materials, electrolytes, and interfacial interactions in overall cell performance, and the importance of nanostructured materials in addressing key challenges. It provides an in-depth analysis of various types of nanostructures, highlighting their roles in improving the electrochemical performance, stability, and durability of SOFCs. Furthermore, this review delves into the fabrication techniques that enable precise control over nanostructure morphology, composition, and architecture. The influence of nanoscale effects on ionic and electronic transport within the electrolyte and electrodes is thoroughly explored, shedding light on the mechanisms behind enhanced performance. By providing a comprehensive overview of the current state of research on nanostructured materials for SOFCs, this review aims to guide researchers, engineers, and policymakers toward the development of high-performance, cost-effective, and sustainable energy conversion systems. Full article

(This article belongs to the Special Issue Advances of Solid Oxide Fuel Cells)

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16 pages, 4641 KiB

Open AccessEditor’s ChoiceArticle

The Impact of Grain Growth on the Functional Properties in Room-Temperature Powder Aerosol Deposited Free-Standing (Ba,Ca)(Zr,Ti)O₃ Thick Films

by Juliana G. Maier, Tim Fuggerer, Daisuke Urushihara, Alexander Martin, Neamul H. Khansur, Ken-ichi Kakimoto and Kyle G. Webber

Crystals 2024, 14(4), 296; https://doi.org/10.3390/cryst14040296 - 22 Mar 2024

Viewed by 1232

Abstract

This study investigates the development of freestanding thick films (FSFs) of lead-free (Ba,Ca)(Zr,Ti)O₃ and the role of grain growth on the electromechanical response. During deposition, room temperature powder aerosol deposition rapidly produces thick films with a nano-grain structure that limits the electromechanical [...] Read more.

This study investigates the development of freestanding thick films (FSFs) of lead-free (Ba,Ca)(Zr,Ti)O₃ and the role of grain growth on the electromechanical response. During deposition, room temperature powder aerosol deposition rapidly produces thick films with a nano-grain structure that limits the electromechanical properties. In this study, the films are removed from the substrate using a sacrificial buffering layer to avoid thermal treatment and allow for an initial as-processed state. Following this, FSFs were thermally treated at various annealing temperatures from 800 °C to 1400 °C to induce grain growth, which was characterized with scanning and transmission electron microscopy. X-ray diffraction revealed an increase in the crystallite size consistent with an increase in grain size and a decrease in internal residual stress. The temperature-dependent dielectric behavior and the large-field ferroelectric response were also characterized, revealing significant differences of the FSFs from the bulk properties. Full article

(This article belongs to the Special Issue Advanced Ferroelectric, Piezoelectric and Dielectric Ceramics)

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10 pages, 1429 KiB

Open AccessEditor’s ChoiceArticle

Revisiting the Crystallography of {225}_γ Martensite: How EBSD Can Help to Solve Long-Standing Controversy

by Loïc Malet and Stéphane Godet

Crystals 2024, 14(3), 287; https://doi.org/10.3390/cryst14030287 - 20 Mar 2024

Viewed by 951

Abstract

Explaining the crystallography of iron alloys martensite with a {225}_γ habit plane remains a challenging task within the phenomenological theory of martensite crystallography. The purpose of this study is to re-examine the martensite formed in a Fe-8Cr-1.1C alloy using EBSD, which has [...] Read more.

Explaining the crystallography of iron alloys martensite with a {225}_γ habit plane remains a challenging task within the phenomenological theory of martensite crystallography. The purpose of this study is to re-examine the martensite formed in a Fe-8Cr-1.1C alloy using EBSD, which has a better angular resolution than the conventional transmission electron diffraction techniques previously used. The results show that the single morphological plates, which hold a near {225}_γ habit plane, are bivariant composites made up of two twin-related variants. It is shown that a {113}_γ plane is systematically parallel to one of the three common

{\{112\}}_{α}

planes between the two twin-related crystals. This observation suggests that the lattice invariant strain of transformation occurs through a dislocation glide on the {113}_γ ⟨110⟩_γ system, rather than through twinning as is commonly accepted. Based on this assumption, the predictions of Bowles and Mackenzie’s original theory are in good agreement with the crystallographic features of {225}_γ martensite. Unexpectedly, it is the high shear solution of the theory that gives the most accurate experimental predictions. Full article

(This article belongs to the Section Crystalline Metals and Alloys)

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12 pages, 3561 KiB

Open AccessEditor’s ChoiceArticle

Comparative Analysis of Room Temperature Structures Determined by Macromolecular and Serial Crystallography

by Ki Hyun Nam

Crystals 2024, 14(3), 276; https://doi.org/10.3390/cryst14030276 - 14 Mar 2024

Cited by 2 | Viewed by 1334

Abstract

Temperature directly influences the function and structure of proteins. Crystal structures determined at room temperature offer more biologically relevant structural information regarding flexibility, rigidity, and thermal motion than those determined by conventional cryocrystallography. Crystal structures can be determined at room temperature using conventional [...] Read more.

Temperature directly influences the function and structure of proteins. Crystal structures determined at room temperature offer more biologically relevant structural information regarding flexibility, rigidity, and thermal motion than those determined by conventional cryocrystallography. Crystal structures can be determined at room temperature using conventional macromolecular crystallography (MX) or serial crystallography (SX) techniques. Among these, MX may theoretically be affected by radiation damage or X-ray heating, potentially resulting in differences between the room temperature structures determined by MX and SX, but this has not been fully elucidated. In this study, the room temperature structure of xylanase GH11 from Thermoanaerobacterium saccharolyticum was determined by MX (RT-TsaGH11-MX). The RT-TsaGH11-MX exhibited both the open and closed conformations of the substrate-binding cleft within the β-sandwich fold. The RT-TsaGH11-MX showed distinct structural changes and molecular flexibility when compared with the RT-TsaGH11 determined via serial synchrotron crystallography. The notable molecular conformation and flexibility of the RT-TsaGH11-MX may be induced by radiation damage and X-ray heating. These findings will broaden our understanding of the potential limitations of room temperature structures determined by MX. Full article

(This article belongs to the Section Macromolecular Crystals)

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13 pages, 6547 KiB

Open AccessEditor’s ChoiceReview

Floating Zone Growth of Pure and Pb-Doped Bi-2201 Crystals

by Maria Roslova, Bernd Büchner and Andrey Maljuk

Crystals 2024, 14(3), 270; https://doi.org/10.3390/cryst14030270 - 11 Mar 2024

Viewed by 1230

Abstract

In this review, we summarize recent progress in crystal growth and understanding of the influence of crystal structure on superconductivity in pure and Pb-doped Bi₂Sr₂CuO_y (Bi-2201) materials belonging to the overdoped region of high-temperature cuprate superconductors. The crystal [...] Read more.

In this review, we summarize recent progress in crystal growth and understanding of the influence of crystal structure on superconductivity in pure and Pb-doped Bi₂Sr₂CuO_y (Bi-2201) materials belonging to the overdoped region of high-temperature cuprate superconductors. The crystal growth of Bi-2201 superconductors faces challenges due to intricate materials chemistry and the lack of knowledge of corresponding phase diagrams. Historically, a crucible-free floating zone method emerged as the most promising growth approach for these materials, resulting in high-quality single crystals. This review outlines the described methods in the literature and the authors’ synthesis endeavors encompassing Pb-doped Bi-2201 crystals, provides a detailed structural characterization of as-grown and post-growth annealed samples, and highlights optimal growth conditions that yield large-size, single-phase, and compositionally homogeneous Bi-2201 single crystals. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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30 pages, 11194 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Exploring Various Crystal and Molecular Structures of Gabapentin—A Review

by Justyna Baranowska and Łukasz Szeleszczuk

Crystals 2024, 14(3), 257; https://doi.org/10.3390/cryst14030257 - 6 Mar 2024

Cited by 1 | Viewed by 1797

Abstract

Novel antiepileptic drugs have been developed at an unparalleled rate during the past 15 years. Gabapentin (GBP), which was approved for the treatment of refractory localization-related epilepsies in the U.K. and Europe in 1993, was one of the first drugs to come out [...] Read more.

Novel antiepileptic drugs have been developed at an unparalleled rate during the past 15 years. Gabapentin (GBP), which was approved for the treatment of refractory localization-related epilepsies in the U.K. and Europe in 1993, was one of the first drugs to come out of this era. Since then, GBP has become well-known across the world, not only for its antiepileptic qualities but also for its effectiveness in the treatment of chronic pain disorders, particularly neuropathic pain. In this review, the crystal structures of GBP and GBP-related compounds have been analyzed and compared. Particular attention has been paid to the polymorphism of GBP and its hydrates, their thermodynamic stability, and conformational differences. In addition, the puckering parameters for the cyclohexane ring of a total of 118 molecules of GBP found in the analyzed crystal structures have been calculated and analyzed. The results of recent high-pressure crystallization studies and quantum chemical calculations indicate that the entire landscape of GBP has not been revealed yet. Full article

(This article belongs to the Special Issue Structural Studies in Drug Discovery and Development: From the Lead to the Pharmaceutical Form)

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11 pages, 8080 KiB

Open AccessEditor’s ChoiceArticle

Synthesis and Crystal Structures of Rhomb-Shaped Dimeric Pd(II) Complexes with Arylethynyl-Substituted 2,2′-Bipyridine through CH⋯π Interactions in the Crystalline States

by Akiko Hori, Reo Ichisugi, Daiki Azegami, Naoki Toyama and Hidetaka Yuge

Crystals 2024, 14(3), 255; https://doi.org/10.3390/cryst14030255 - 5 Mar 2024

Cited by 1 | Viewed by 1068

Abstract

Two molecular structures of a complex C₂₆H₁₆Cl₂N₂Pd (1) with a benzene hemisolvate (1•0.5C₆H₆) and a complex C₃₄H₂₀Cl₂N₂Pd (2 [...] Read more.

Two molecular structures of a complex C₂₆H₁₆Cl₂N₂Pd (1) with a benzene hemisolvate (1•0.5C₆H₆) and a complex C₃₄H₂₀Cl₂N₂Pd (2) revealed similar conformations: one side of the arylethynyl group is flat to the bipyridine plane while the other side of the arylethynyl group is highly twisted to the plane because rhomb-like dimer fragments are formed between respective two complexes through CH⋯π interactions. The Hirshfeld surface analysis indicates that the most important contributions for the crystal packing of 1 are from H⋯H (33.6%), C⋯H/H⋯C (28.3%), Cl⋯H/H⋯Cl (17.8%), and C⋯C (10.6%) interactions and those of 2 are from H⋯H (36.5%), C⋯H/H⋯C (26.0%), Cl⋯H/H⋯Cl (15.7%), and C⋯C (12.3%) interactions, indicating the remarkable CH⋯π and electron distribution of molecules by Cl ions. The benzene solvate molecule of 1•0.5C₆H₆ performs to fill the internal space instead of the naphthyl group. Detailed crystallographic and DFT studies were performed to understand the molecular structures and the corresponding supramolecular associations. Full article

(This article belongs to the Section Organic Crystalline Materials)

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14 pages, 4766 KiB

Open AccessEditor’s ChoiceArticle

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

Viewed by 1236

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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19 pages, 7580 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Hydrate Formation with the Memory Effect Using Classical Nucleation Theory

by I. Yucel Akkutlu, Emre Arslan and Faisal Irshad Khan

Crystals 2024, 14(3), 243; https://doi.org/10.3390/cryst14030243 - 29 Feb 2024

Viewed by 1068

Abstract

Methane hydrate formation is analytically studied in the presence of the water memory effect using the classical nucleation theory. The memory effect is introduced as a change in nucleation site from a three-dimensional heterogenous nucleation on a solid surface with cap-shaped hydrate clusters [...] Read more.

Methane hydrate formation is analytically studied in the presence of the water memory effect using the classical nucleation theory. The memory effect is introduced as a change in nucleation site from a three-dimensional heterogenous nucleation on a solid surface with cap-shaped hydrate clusters (3D-HEN) to a two-dimensional nucleation on the solid hydrate residue surface with monolayer disk-shaped hydrate clusters (2D-NOH). The analysis on the stationary nucleation of methane hydrate under isobaric conditions shows that the memory effect caused an average decrease of 4.4 K in metastable zone width, or subcooling. This decrease can be erased at higher dissociation temperatures (ΔT > 17.2 K) due to a decrease in the concentration of 2D-NOH nucleation sites. Moreover, the probability of hydrate formation is estimated for the purpose of quantifying risk associated with methane hydrate formation in the presence of the memory effect. Full article

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14 pages, 10069 KiB

Open AccessEditor’s ChoiceArticle

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

Viewed by 1035

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

Δ T

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,

Δ T > 160

K (namely, for samples solidified with

Δ T = 170

K and

Δ T = 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

Δ T \approx 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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31 pages, 9156 KiB

Open AccessFeature PaperEditor’s ChoiceReview

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

Viewed by 3538

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

Open AccessFeature PaperEditor’s ChoiceArticle

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 1058

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

Open AccessEditor’s ChoiceArticle

The Crystal Structure and Physicochemical Properties of New Complexes Containing a Cu^II-Ln^III-Cu^II Core

by Beata Cristóvão, Dariusz Osypiuk and Barbara Mirosław

Crystals 2024, 14(2), 189; https://doi.org/10.3390/cryst14020189 - 14 Feb 2024

Viewed by 1145

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 Cu^II ions are five- and six-coordinate, with distorted square pyramidal and octahedral geometry, respectively, whereas the Ln^III 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 Cu^II and Tb^III/Ho^III 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

Open AccessEditor’s ChoiceArticle

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 1 | Viewed by 1587

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

Open AccessEditor’s ChoiceArticle

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 1767

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

10^{10}

/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

Open AccessEditor’s ChoiceArticle

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 2 | Viewed by 1024

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, 7575 KiB

Open AccessEditor’s ChoiceArticle

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

Viewed by 1112

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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22 pages, 8785 KiB

Open AccessEditor’s ChoiceArticle

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 2 | Viewed by 1289

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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21 pages, 10223 KiB

Open AccessEditor’s ChoiceArticle

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

Viewed by 904

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

Open AccessFeature PaperEditor’s ChoiceArticle

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

Viewed by 1271

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

Open AccessEditor’s ChoiceReview

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 2 | Viewed by 2389

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

Open AccessEditor’s ChoiceArticle

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

Viewed by 1725

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

Open AccessEditor’s ChoiceArticle

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

Viewed by 1400

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 (Ce_1−xZr_xO₂, [...] 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 (Ce_1−xZr_xO₂, 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

Open AccessEditor’s ChoiceReview

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 1846

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

Open AccessEditor’s ChoiceArticle

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

Viewed by 1032

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

Open AccessEditor’s ChoiceArticle

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

Viewed by 845

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

Open AccessEditor’s ChoiceArticle

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 1 | Viewed by 1458

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

Open AccessEditor’s ChoiceArticle

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

Viewed by 1430

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

Open AccessEditor’s ChoiceArticle

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 1029

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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15 pages, 6390 KiB

Open AccessEditor’s ChoiceArticle

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 1 | Viewed by 1305

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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13 pages, 1940 KiB

Open AccessEditor’s ChoiceArticle

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 1112

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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11 pages, 8281 KiB

Open AccessEditor’s ChoiceArticle

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

Viewed by 1055

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 RbTiOPO

_{4}

(RbTiPO

_{4}

F, 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 RbTiOPO

_{4}

(RbTiPO

_{4}

F, 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 KTiOPO

_{4}

(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 Ti

^{3 +}

to Ti

^{4 +}

) 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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15 pages, 5055 KiB

Open AccessFeature PaperEditor’s ChoiceReview

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 1360

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

Open AccessEditor’s ChoiceArticle

Synthesis and Structural Characterization of Layered Ni^+1/+2 Oxides Obtained by Topotactic Oxygen Release on Nd_2−xSr_xNiO_4−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

Viewed by 1193

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 d_z² vs. d_x²−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 Nd_2−xSr_xNiO_4+δ single crystals, which are then reduced by H₂ gas, forming Nd_2−xSr_xNiO_4−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

Open AccessEditor’s ChoiceArticle

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 1065

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

Open AccessEditor’s ChoiceArticle

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

Viewed by 1037

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

Open AccessEditor’s ChoiceArticle

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 1168

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

Open AccessEditor’s ChoiceArticle

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 3 | Viewed by 1498

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 SiN_X/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 SiN_X/SiO₂ dielectric field plate edge termination was employed to increase the breakdown voltage (V_B). These heterojunction rectifiers exhibit remarkable simultaneous achievement of high breakdown voltage and substantial conducting currents. In particular, the devices manifest V_B 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 V_B 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 V_B 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 V_B²/R_ON, reveals a value of 9.2 GW·cm⁻², where R_ON denotes the on-state resistance, measuring 5.4 mΩ·cm². The Coff was 4 nF/cm², leading to an R_ON × C_off of 34 ps and F_CO 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

Open AccessEditor’s ChoiceReview

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 2 | Viewed by 1717

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

Open AccessEditor’s ChoiceArticle

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

Viewed by 901

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

Open AccessEditor’s ChoiceArticle

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 1478

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(Zr_0.52Ti_0.48)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

Open AccessEditor’s ChoiceArticle

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 1324

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

Open AccessEditor’s ChoiceArticle

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 1 | Viewed by 1262

Abstract

A single crystal of ytterbium-doped “mixed” yttrium–lutetium aluminum garnet with a stoichiometric composition of (Y_0.601Lu_0.233Yb_0.166)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 (Y_0.601Lu_0.233Yb_0.166)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 ²F_5/2 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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Open AccessEditor’s ChoiceArticle

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 1 | Viewed by 1265

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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