Crystals

12 pages, 6459 KiB

Open AccessArticle

Design, Manufacturing, Microstructure, and Surface Properties of Brazed Co-Based Composite Coatings Reinforced with Tungsten Carbide Particles

by Ion-Dragoș Uțu, Iasmina-Mădălina Anghel (Petculescu), Iosif Hulka and Gabriela Marginean

Crystals 2024, 14(6), 576; https://doi.org/10.3390/cryst14060576 - 20 Jun 2024

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Abstract

Brazing is a joining process that involves melting a filler metal and flowing it into the joint between two closely fitting parts. While brazing is primarily used for joining metals, it can also be adapted for certain coating deposition applications. The present study [...] Read more.

Brazing is a joining process that involves melting a filler metal and flowing it into the joint between two closely fitting parts. While brazing is primarily used for joining metals, it can also be adapted for certain coating deposition applications. The present study investigates the microstructure and corrosion behavior and sliding wear resistance of WC (Tungsten Carbide)-CoCr-Ni reinforced Co-based composite coatings deposited onto the surface of AISI 904L stainless steel using a vacuum brazing method. The primary objective of this experimental work was to evaluate the influence of WC-based particles added to the microstructure and the properties of the brazed Co composite coating. The focus was on enhancing the sliding wear resistance of the coatings while ensuring that their corrosion resistance in chloride media was not adversely affected. The morphology and microstructure of the composite coatings were investigated using scanning electron microscopy (SEM) and phase identification by X-ray diffraction (XRD). The SEM analysis revealed in the coating the presence of intermetallic compounds and carbides, which increase the hardness of the material. The sliding wear resistance was assessed using the pin-on-disk method, and the corrosion properties were determined using electrochemical measurements. The results obtained showed that as the WC particle ratio in the Co-based composite coating increased, the mechanical properties improved, the alloy became harder, and the tribological properties were improved. The evaluation of the electrochemical tests revealed no significant alterations of the manufactured composite in comparison with the Co-based alloys. In all cases, the corrosion behavior was better compared with that of the stainless-steel substrate. Full article

(This article belongs to the Special Issue Modern Technologies in the Manufacturing of Metal Matrix Composites)

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14 pages, 6653 KiB

Open AccessArticle

An Effect of Boric Acid on the Structure and Luminescence of Yttrium Orthoborates Doped with Europium Synthesized by Two Different Routines

by Irena P. Kostova, Tinko A. Eftimov, Katya Hristova, Stefka Nachkova, Slava Tsoneva and Alexandar Peltekov

Crystals 2024, 14(6), 575; https://doi.org/10.3390/cryst14060575 - 20 Jun 2024

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Abstract

In this paper, we present the characteristics of photoluminescent YBO₃ successfully synthesized through a solid-state reaction and a microwave-assisted method. We used yttrium oxide and boric acid in excess as the starting reagents. The synthesis conditions were reflected in the fluorescent characteristics [...] Read more.

In this paper, we present the characteristics of photoluminescent YBO₃ successfully synthesized through a solid-state reaction and a microwave-assisted method. We used yttrium oxide and boric acid in excess as the starting reagents. The synthesis conditions were reflected in the fluorescent characteristics and the structure. Excess boric acid caused structural changes, as observed by the FTIR spectroscopy analysis. Powder X-ray diffraction (XRD) analysis confirmed the crystalline phases and purity of the samples. We observed improved photoluminescence properties in the samples synthesized by the microwave-assisted method. These findings enhance the understanding of the material’s properties and indicate potential applications in illumination, displays, and narrow-band fluorescent smartphone-readable markers. Full article

(This article belongs to the Special Issue Rare Earths-Doped Materials (3rd Edition))

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18 pages, 6189 KiB

Open AccessArticle

Mechanical Properties of Ti Grade 2 Manufactured Using Laser Beam Powder Bed Fusion (PBF-LB) with Checkerboard Laser Scanning and In Situ Oxygen Strengthening

by Bartlomiej Adam Wysocki, Agnieszka Chmielewska-Wysocka, Piotr Maj, Rafał Maksymilian Molak, Barbara Romelczyk-Baishya, Łukasz Żrodowski, Michał Ziętala, Wojciech Nowak, Wojciech Święszkowski and Marek Muzyk

Crystals 2024, 14(6), 574; https://doi.org/10.3390/cryst14060574 - 20 Jun 2024

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Abstract

Additive manufacturing (AM) technologies have advanced from rapid prototyping to becoming viable manufacturing solutions, offering users both design flexibility and mechanical properties that meet ISO/ASTM standards. Powder bed fusion using a laser beam (PBF-LB), a popular additive manufacturing process (aka 3D printing), is [...] Read more.

Additive manufacturing (AM) technologies have advanced from rapid prototyping to becoming viable manufacturing solutions, offering users both design flexibility and mechanical properties that meet ISO/ASTM standards. Powder bed fusion using a laser beam (PBF-LB), a popular additive manufacturing process (aka 3D printing), is used for the cost-effective production of high-quality products for the medical, aviation, and automotive industries. Despite the growing variety of metallic powder materials available for the PBF-LB process, there is still a need for new materials and procedures to optimize the processing parameters before implementing them into the production stage. In this study, we explored the use of a checkerboard scanning strategy to create samples of various sizes (ranging from 130 mm³ to 8000 mm³ using parameters developed for a small 125 mm³ piece). During the PBF-LB process, all samples were fabricated using Ti grade 2 and were in situ alloyed with a precisely controlled amount of oxygen (0.1–0.4% vol.) to enhance their mechanical properties using a solid solution strengthening mechanism. The samples were fabricated in three sets: I. Different sizes and orientations, II. Different scanning strategies, and III. Rods for high-cycle fatigue (HCF). For the tensile tests, micro samples were cut using WEDM, while for the HCF tests, samples were machined to eliminate the influence of surface roughness on their mechanical performance. The amount of oxygen in the fabricated samples was at least 50% higher than in raw Ti grade 2 powder. The O₂-enriched Ti produced in the PBF-LB process exhibited a tensile strength ranging from 399 ± 25 MPa to 752 ± 14 MPa, with outcomes varying based on the size of the object and the laser scanning strategy employed. The fatigue strength of PBF-LB fabricated Ti was 386 MPa, whereas the reference Ti grade 2 rod samples exhibited a fatigue strength of 312 MPa. Our study revealed that PBF-LB parameters optimized for small samples could be adapted to fabricate larger samples using checkerboard (“island”) scanning strategies. However, some additional process parameter changes are needed to reduce porosity. Full article

(This article belongs to the Special Issue Laser–Material Interaction: Principles, Phenomena, and Applications)

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12 pages, 5475 KiB

Open AccessArticle

Printing Direction Effects on the Sliding Contact Response of a Binder Jetting 3D-Printed WC-Co Hardmetal

by Laura Cabezas, Christian Berger, Emilio Jiménez-Piqué, Johannes Pötschke and Luis Llanes

Crystals 2024, 14(6), 573; https://doi.org/10.3390/cryst14060573 - 20 Jun 2024

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Abstract

Binder jetting additive manufacturing offers a promising route to produce complex geometries in cemented carbides (WC-Co), but it may introduce direction-dependent microstructural variations potentially affecting wear resistance. This study investigates the influence of printing direction on the sliding contact response of 3D-printed and [...] Read more.

Binder jetting additive manufacturing offers a promising route to produce complex geometries in cemented carbides (WC-Co), but it may introduce direction-dependent microstructural variations potentially affecting wear resistance. This study investigates the influence of printing direction on the sliding contact response of 3D-printed and subsequently sintered (BJT) WC-12%Co. Prismatic specimens were printed along two orientations and subjected to single and repetitive scratch tests on three orthogonal faces. The microstructure, Vickers and scratch hardness, and wear rate were analyzed. The results showed a heterogeneous microstructure consisting of a matrix of fine carbides where several large particles where embedded. It was different from the homogenous microstructural scenarios exhibited by conventionally pressed and sintered fine- and coarse-grained hardmetals, used as reference for comparison purposes. The influence of printing direction on either the microstructure or mechanical properties of BJT specimens was found to be negligible. Interestingly, BJT samples exhibited superior wear resistance than the reference hardmetals, even though the hardness levels were alike for all the studied hardmetal grades. Such behavior is attributed to the co-existence of coarse and fine carbides within the microstructure, combining the energy absorption capability of the former with the inherent strength of the latter. These findings, together with the intrinsic flexibility and versatility advantages associated with additive manufacturing, highlight the potential of BJT hardmetals to be used in applications where contact load bearing or wear resistance are critical design parameters. Finally, the effectiveness of implementing an iterative sliding contact test for evaluating wear behavior in cemented carbides was also validated. Full article

(This article belongs to the Special Issue Advances in New Multifunctional Hard Materials)

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13 pages, 3371 KiB

Open AccessArticle

Tuning Fe₂Ti Distribution to Enhance Extrinsic Magnetic Properties of SmFe₁₂-Based Magnets

by Jinbo Wei, Shuainan Xu, Chengyuan Xu, Xiaolian Liu, Yu Pan, Wei Wang, Yue Wu, Ping Chen, Jun Liu, Lizhong Zhao and Xuefeng Zhang

Crystals 2024, 14(6), 572; https://doi.org/10.3390/cryst14060572 - 20 Jun 2024

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Abstract

The ThMn₁₂-type SmFe₁₂-based rare-earth permanent magnet has attracted widespread attention due to its excellent intrinsic magnetic properties and high-temperature stability. However, the challenge in realizing continuous non-magnetic or weakly magnetic grain boundary phases equilibrated with the SmFe₁₂ main [...] Read more.

The ThMn₁₂-type SmFe₁₂-based rare-earth permanent magnet has attracted widespread attention due to its excellent intrinsic magnetic properties and high-temperature stability. However, the challenge in realizing continuous non-magnetic or weakly magnetic grain boundary phases equilibrated with the SmFe₁₂ main phase hinders the enhancement in extrinsic magnetic properties of the SmFe₁₂-based permanent magnet, especially for the coercivity. In this work, by controlling the cooling rate, the uniform distribution of paramagnetic Fe₂Ti phases at grain boundaries is achieved in the SmFe₁₂-based alloy ribbon, resulting in a high coercivity of 7.95 kOe. This improvement is attributed to the elimination of the impurity phase within the SmFe₁₂ main phase and the magnetic isolation effect of the grain boundary phase composed of paramagnetic Fe₂Ti, which is directly observed by transmission electron microscopy and further confirmed by micromagnetic simulation. Moreover, first-principles calculations show that the V element can dope into Fe₂Ti and facilitate the transition of its paramagnetic state at room temperature. This study provides new insights into constructing weakly magnetic grain boundary phases for SmFe₁₂-based permanent magnets, offering a novel approach to enhance coercivity. Full article

(This article belongs to the Special Issue The Synthesis and Prospects of Magnetic Materials)

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13 pages, 4121 KiB

Open AccessArticle

The Impact of Curing Temperature and UV Light Intensity on the Performance of Polymer-Dispersed Liquid Crystal Devices Exhibiting a Permanent Memory Effect

by Ana Mouquinho and João Sotomayor

Crystals 2024, 14(6), 571; https://doi.org/10.3390/cryst14060571 - 20 Jun 2024

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Abstract

PDLC films, synthesized via polymerization-induced phase separation (PIPS) utilizing both temperature and UV monochromatic radiation, were derived from a blend of E7 nematic liquid crystal (LC) and PolyEGDMA875 (polyethyleneglycoldimethacrylate) oligomers, serving as the precursor for the polymeric matrix. The influence of the curing [...] Read more.

PDLC films, synthesized via polymerization-induced phase separation (PIPS) utilizing both temperature and UV monochromatic radiation, were derived from a blend of E7 nematic liquid crystal (LC) and PolyEGDMA875 (polyethyleneglycoldimethacrylate) oligomers, serving as the precursor for the polymeric matrix. The influence of the curing temperature on thermal polymerization, UV light intensity on photochemical polymerization, and exposure time during these processes on the electro-optical characteristics of PDLC films was thoroughly examined. Observations revealed that employing thermal polymerization during device preparation notably enhanced the permanent memory effect of the PDLC films. Sustained high transparency (T_OFF = 45%) over an extended duration at room temperature, even subsequent to voltage cessation, was achieved. This transition initiated from an opaque state (T₀ = 0%) through to a transparent state (T_MAX = 65%), resulting in a substantial 70% permanent memory effect. Full article

(This article belongs to the Special Issue Optoelectronics of Thin Films and Nanoparticles (2nd Edition))

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15 pages, 3621 KiB

Open AccessArticle

Completing the Ba–As Compositional Space: Synthesis and Characterization of Three New Binary Zintl Arsenides, Ba₃As₄, Ba₅As₄, and Ba₁₆As₁₁

by Spencer R. Watts, Lindsey M. Wingate, Svilen Bobev and Sviatoslav Baranets

Crystals 2024, 14(6), 570; https://doi.org/10.3390/cryst14060570 - 20 Jun 2024

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Abstract

Three novel binary barium arsenides, Ba₃As₄, Ba₅As₄, and Ba₁₆As₁₁, were synthesized and their crystal and electronic structures were investigated. Structural data collected via the single-crystal X-ray diffraction method indicate that the [...] Read more.

Three novel binary barium arsenides, Ba₃As₄, Ba₅As₄, and Ba₁₆As₁₁, were synthesized and their crystal and electronic structures were investigated. Structural data collected via the single-crystal X-ray diffraction method indicate that the anionic substructures of all three novel compounds are composed of structural motifs based on the homoatomic As–As contacts, with [As₂]⁴⁻ dimers found in Ba₅As₄ and Ba₁₆As₁₁, and an [As₄]⁶⁻ tetramer found in Ba₃As₄. Ba₃As₄ and Ba₅As₄ crystallize in the orthorhombic crystal system—with the non-centrosymmetric space group Fdd2 (a = 15.3680(20) Å, b = 18.7550(30) Å, c = 6.2816(10) Å) for the former, and the centrosymmetric space group Cmce (a = 16.8820(30) Å, b = 8.5391(16) Å, and c = 8.6127(16) Å) for the latter—adopting Eu₃As₄ and Eu₅As₄ structure types, respectively. The heavily disordered Ba₁₆As₁₁ structure was solved in the tetragonal crystal system with the space group

P \bar{4} 2_{1} m

(a = 12.8944(12) Å and c = 11.8141(17) Å). The Zintl concept can be applied to each of these materials as follows: Ba₃As₄ = (Ba²⁺)₃[As₄]⁶⁻, Ba₅As₄ = (Ba²⁺)₅(As³⁻)₂[As₂]⁴⁻, and 2 × Ba₁₆As₁₁ = (Ba²⁺)₃₂(As³⁻) ≈ ₂₀[As₂]⁴⁻ ≈ 1, pointing to the charge-balanced nature of these compounds. Electronic structure calculations indicate narrow bandgap semiconducting behavior, with calculated bandgaps of 0.47 eV for Ba₃As₄, 0.34 eV for Ba₅As₄, and 0.33 eV for Ba₁₆As₁₁. Full article

(This article belongs to the Special Issue Research on Thermoelectric Materials: Waste Heat into Renewable Energy)

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18 pages, 28935 KiB

Open AccessArticle

The Effect of Varying Parameters of Laser Surface Alloying Post-Treatment on the Microstructure and Hardness of Additively Manufactured 17-4PH Stainless Steel

by Alexander S. Chaus, Oleg G. Devoino, Martin Sahul, Ľubomír Vančo and Ivan Buranský

Crystals 2024, 14(6), 569; https://doi.org/10.3390/cryst14060569 - 20 Jun 2024

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Abstract

In the present work, the evolution of the microstructure in additively manufactured 17-4PH stainless steel, which was subjected to laser surface alloying with amorphous boron and nitrogen at the varying process parameters, was studied. The main aim was to improve surface hardness and [...] Read more.

In the present work, the evolution of the microstructure in additively manufactured 17-4PH stainless steel, which was subjected to laser surface alloying with amorphous boron and nitrogen at the varying process parameters, was studied. The main aim was to improve surface hardness and hence potential wear resistance of the steel. Scanning electron microscopy, wavelength-dispersive X-ray spectroscopy (WDS), and Auger electron spectroscopy (AES) were used. It was shown that the final microstructure developed in the laser-melted zone (LMZ) is dependent on a variety of processing parameters (1 and 1.5 mm laser beam spot diameters; 200, 400, and 600 mm/min laser scan speeds), which primarily influence the morphology and orientation of the eutectic dendrites in the LMZ. It was metallographically proven that a fully eutectic microstructure, except for one sample containing 60 ± 4.2% of the eutectic, was revealed in the LMZ in the studied samples. The results of WDS and AES also confirmed alloying the LMZ with nitrogen. The formation of the boron eutectic and the supersaturation of the α-iron solid solution with boron and nitrogen (as a part of the eutectic mixture) led to enhanced microhardness, which was significantly higher compared with that of the heat-treated substrate (545.8 ± 12.59–804.7 ± 19.4 vs. 276.8 ± 10.1–312.7 ± 11.7 HV0.1). Full article

(This article belongs to the Special Issue Advances in Surface Modifications of Metallic Materials)

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11 pages, 3370 KiB

Open AccessArticle

Enantiopurification by Co-Crystallization within Cyclodextrin Metal–Organic Framework

by Masoud Kazem-Rostami, Pardis Shirdast and Kalidas Mainali

Crystals 2024, 14(6), 568; https://doi.org/10.3390/cryst14060568 - 19 Jun 2024

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Abstract

Tröger’s base analogs (TBAs) and their derivatives are versatile, Λ-shaped, tetracyclic chiral building blocks utilized in numerous fields of research. Although various methods for the enantiopurification of TBAs have been demonstrated in the literature, none has achieved it with the use of metal–organic [...] Read more.

Tröger’s base analogs (TBAs) and their derivatives are versatile, Λ-shaped, tetracyclic chiral building blocks utilized in numerous fields of research. Although various methods for the enantiopurification of TBAs have been demonstrated in the literature, none has achieved it with the use of metal–organic frameworks (MOFs). This investigation introduces a convenient and scalable method to obtain enantiopure TBAs with the formation and digestion of a chiral MOF composed of fully recoverable and non-hazardous starting materials, namely, cyclodextrin-based metal–organic framework (CD-MOF). Full article

(This article belongs to the Section Organic Crystalline Materials)

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16 pages, 3433 KiB

Open AccessCommunication

Metal Ion Microwave-Assisted Depolymerization of Poly(Ethylene Terephthalate): A Zinc Salts-Based Deep Eutectic Solvent as Case Study

by Cosimo Ricci, Lorenzo Gontrani, Elvira Maria Bauer, Giorgia Ciufolini, Angelo Lembo, Lorenzo Casoli and Marilena Carbone

Crystals 2024, 14(6), 567; https://doi.org/10.3390/cryst14060567 - 19 Jun 2024

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Abstract

In this study, a new and very quick method to depolymerize PET plastics is reported. The depolymerization experiments were conducted using a type-IV deep eutectic solvent containing ZnCl₂ and urea, and a microwave oven as reactor. Different combinations of power and reaction [...] Read more.

In this study, a new and very quick method to depolymerize PET plastics is reported. The depolymerization experiments were conducted using a type-IV deep eutectic solvent containing ZnCl₂ and urea, and a microwave oven as reactor. Different combinations of power and reaction times were employed while keeping the total energy constant. Successful conversions were obtained carrying out the process at 180 W for 2 min and 360 W for 1 min, whereas at higher powers and shorter times, an inclusion likely occurs of some solvent into the structure of the recovered PET flakes, as suggested by the porosity of the flakes, imaged by SEM microscopy. The flakes increase their crystalline character during the treatment, as indicated by the appearance of narrow diffraction peaks in the XRD patterns, at variance with the broad signals observed in the case of the pristine amorphous polymer. The NMR analysis of the supernatant liquid above the partially solubilized PET shows the presence of terephthalic acid peaks. The infrared spectra of the solid powder achieved upon the acidic treatment of the extract reveal the presence of C=O stretching peaks and the absence of typical CH₂ wagging absorptions that satisfactorily comply with the presence of terephthalic acid. Full article

(This article belongs to the Section Macromolecular Crystals)

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19 pages, 9184 KiB

Open AccessArticle

Investigating the Role of CNP and CNP Aggregates in the Rheological Breakdown of Triglyceride Systems

by Ivana A. Penagos, Fien De Witte, Tom Rimaux, Koen Dewettinck and Filip Van Bockstaele

Crystals 2024, 14(6), 566; https://doi.org/10.3390/cryst14060566 - 19 Jun 2024

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Abstract

In many food applications, the mechanical properties of fats play a critical role in determining the processing performance of fat-rich products. In fact, fat crystal networks form a particular class of soft materials that exhibit viscoelastic properties. The uniqueness of the mechanical response [...] Read more.

In many food applications, the mechanical properties of fats play a critical role in determining the processing performance of fat-rich products. In fact, fat crystal networks form a particular class of soft materials that exhibit viscoelastic properties. The uniqueness of the mechanical response is intricately linked to the hierarchical nature of the system, as fats possess a complex architecture encompassing features at different scale levels (i.e., length scales). Since the discovery of crystalline nanoplatelets (CNPs), it has been hypothesized that CNPs are the basic building blocks of lipid networks and that CNPs are the responsible units for the mechanical properties of fats. This hypothesis, however, has only been partially tested. In this article, we examine which units could be responsible (e.g., lamellae, CNP, CNP aggregates) for the mechanical breakdown of fat crystal networks, through Rheo-USAXS in beamline ID02 (ESRF, Grenoble, France). Time-resolved USAXS profiles were acquired during the three steps of a three-interval thixotropy test (3iTT), namely, pre-shear, shear and recovery. The results were then utilized to evidence which specific length scale is arranged (i.e., orientated) during rheological breakdown. The findings suggest that, at the tested shear rates, orientation is only visible from 250 nm onwards, suggesting that the rheological breakdown of triglycerides is primarily driven by the orientation, and possible disruption, of CNP aggregates. These results reveal the critical role of CNP aggregates in the mechanical properties of fats. In the longer term, we believe this study will steer future research toward a more focused understanding of CNP aggregation and disaggregation dynamics. Full article

(This article belongs to the Special Issue Green Approach in Synthesis of Bio-Inspired Materials (Second Edition))

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14 pages, 3921 KiB

Open AccessArticle

The Electrical Resistivity of Liquid Fe-16wt%S-2wt%Si at High Pressures and the Effect of S and Si on the Dynamo in the Ancient Vestan Core

by Erin M. Lenhart, Wenjun Yong and Richard A. Secco

Crystals 2024, 14(6), 565; https://doi.org/10.3390/cryst14060565 - 19 Jun 2024

Viewed by 444

Abstract

A critical component of predicting thermal convection and dynamo action in the cores of terrestrial planetary bodies is the adiabatic heat flux at the top of the core. Powders of Fe, FeS, and Fe-9wt%Si were mixed to imitate the core of Asteroid 4 [...] Read more.

A critical component of predicting thermal convection and dynamo action in the cores of terrestrial planetary bodies is the adiabatic heat flux at the top of the core. Powders of Fe, FeS, and Fe-9wt%Si were mixed to imitate the core of Asteroid 4 Vesta, which studies of HED meteorites indicate is comprised of 13–16wt%S and 1–2wt%Si. In a 1000-ton cubic anvil press, the voltage drop across an Fe-16wt%S-2wt%Si sample of 8–10 mm³ was measured at 2, 3, 4, and 5 GPa and ~300–2000 K. The resistivity of Fe-16wt%S-2wt%Si is 400 ± 50 μΩ·cm for 2–5 GPa for the complete liquid state. Using the Wiedemann–Franz Law, this gives an electronic thermal conductivity of 11 ± 1.5 W/m/K for 2–4 GPa at complete melting and an adiabatic heat flow of 55 ± 15 MW at the top of an early Fe-16wt%S-2wt%Si Vestan core. The 2 GPa boundary of the miscibility of Fe-16wt%S-2wt%Si is observed. The adiabatic heat flow through an Fe-16wt%S-2wt%Si core of variable size is discussed, as well as the resistivity of liquid Fe alloy at small planetary core conditions as a function of S and Si alloying composition. On the basis of previous studies on binary and ternary alloys of Fe with S and/or Si, we interpolate the separate effects of S and Si on the resistivity (and inversely on thermal conductivity and core adiabatic heat flow). Full article

(This article belongs to the Special Issue New Trends in Magnetic, Dielectric, Electrical, Optical, and Thermal Properties of Crystalline Materials)

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12 pages, 3985 KiB

Open AccessArticle

Modelling and Control of Thermal Stress in TSLAG (Tb₃Sc_1.95Lu_0.05Al₃O₁₂) Magneto-Optical Crystals Grown by Czochralski Method

by Junling Ding, Yu Zhang, Yuankai Hao and Xiuwei Fu

Crystals 2024, 14(6), 564; https://doi.org/10.3390/cryst14060564 - 18 Jun 2024

Viewed by 261

Abstract

Tb₃Sc_1.95Lu_0.05Al₃O₁₂ (TSLAG) crystals are novel and high-quality magneto-optical materials with the most promising application as the core component of Faraday devices. Cracking is an obstacle to TSLAG crystal growth and is closely influenced by [...] Read more.

Tb₃Sc_1.95Lu_0.05Al₃O₁₂ (TSLAG) crystals are novel and high-quality magneto-optical materials with the most promising application as the core component of Faraday devices. Cracking is an obstacle to TSLAG crystal growth and is closely influenced by crystal thermal stress distribution. In this work, the evolution of thermal stress during TSLAG crystal growth in the initial Czochralski (Cz) furnace is numerically studied. The reasons for high thermal stress in TSLAG crystal are explained based on the results about the melt flow, the temperature distribution in the furnace, and the crystal/melt interface shape. A large crucible with a shallow melt is proposed to address the problem of significant variations in melt depth during TSLAG crystal growth. Based on the numerical results, the proposed design can stabilize the melt flow structure, suppressing changes in the crystal/melt interface shape and effectively improving thermal stress in the TSLAG crystal growth process, which contributes to precisely regulating the preparation of large-sized high-quality TSLAG crystals. Full article

(This article belongs to the Special Issue Crystallization Process and Simulation Calculation, Second Edition)

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9 pages, 1587 KiB

Open AccessArticle

In Situ Calculation of the Rotation Barriers of the Methyl Groups of Tribromomesitylene Crystals: Theory Meets Experiment

by Anissa Amar, Soria Zeroual, Xavier Rocquefelte and Abdou Boucekkine

Crystals 2024, 14(6), 563; https://doi.org/10.3390/cryst14060563 - 18 Jun 2024

Viewed by 282

Abstract

The computation of the rotation barriers of the methyl groups (Me) of tribromomesitylene (TBM) crystals has been carried out. Experimentally, the barriers of the three Me groups of TBM are found to be high and different. These groups do not experience the same [...] Read more.

The computation of the rotation barriers of the methyl groups (Me) of tribromomesitylene (TBM) crystals has been carried out. Experimentally, the barriers of the three Me groups of TBM are found to be high and different. These groups do not experience the same hindering environment in the crystal state. For an isolated TBM molecule, the three barriers are equal and very low. We found that a cluster of 21 TBM molecules permits the reproduction of the crystal symmetry and structure of the bulk, with a central molecule surrounded by six molecules in the same plane and seven other molecules in two planes above and below. DFT computations including dispersion corrections have been carried out using the ONIOM procedure. The Me groups of the central TBM molecule were rotated step by step to determine the conformations of lowest and highest energy for each Me, thus allowing estimation of the rotation barriers as the difference between these energies. In doing so, we found the following barrier values, namely 105, 173, and 205 cm⁻¹, whereas the experimental values were 111, 180 and 200 cm⁻¹. Full article

(This article belongs to the Special Issue Advances in Machine Learning for Atomistic Simulations: Paving the Way for Next-Generation Material Design)

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24 pages, 66534 KiB

Open AccessArticle

Effect of Preparation Process on the Microstructure and Characteristics of TiAl Pre-Alloyed Powder Fabricated by Plasma Rotating Electrode Process

by Yu Zhang, Meihui Song, Yan Li, Yanchun Li, Shulin Gong and Bin Zhang

Crystals 2024, 14(6), 562; https://doi.org/10.3390/cryst14060562 - 18 Jun 2024

Viewed by 267

Abstract

TiAl pre-alloyed powder is the foundation for additive manufacturing of TiAl alloys. In this work, TiAl pre-alloyed powder was prepared using a plasma rotating electrode process (PREP). The effects of electrode rotating speeds and current intensity on the microstructure and characteristics of TiAl [...] Read more.

TiAl pre-alloyed powder is the foundation for additive manufacturing of TiAl alloys. In this work, TiAl pre-alloyed powder was prepared using a plasma rotating electrode process (PREP). The effects of electrode rotating speeds and current intensity on the microstructure and characteristics of TiAl pre-alloyed powder have been investigated in detail. The results show that the electrode rotating speeds mainly affected the average particle size of the powder (D50). As the electrode rotating speed increased, the D50 of the powder decreased. The current intensity mainly affected the particle size distribution of the powder. As the current intensity increased, the particle size distribution of the powder became narrower, which was concentrated at 45~105 μm. In addition, the current intensity had a significant effect on the sphericity degree of the powder with the particle size > 105 μm, but it had little effect on that <105 μm powder. TiAl pre-alloyed powder with a particle size > 45 μm demonstrated a dendritic + cellular structure, and the <45 μm powder had a microcrystalline structure. The powder was mainly composed of the α₂ phase and γ phase. There were two kinds of phase structure inside the powder, namely the α₂ + γ lamellar microstructure (particle size < 45 µm) and the α₂ + γ network microstructure (particle size > 45 µm). The phase structure of the powder was related to the solidification path and cooling rate of molten droplets in the PREP. The average thickness of the α₂ + γ lamellar was about 200 nm, in which the lamellar γ phases were arranged in an orderly manner in the α₂ phase matrix with a thickness of about 20 nm. The network phase structure was corrugated, and the morphology of the γ phase was not obvious. Full article

(This article belongs to the Special Issue Progress in Light Alloys)

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19 pages, 10925 KiB

Open AccessArticle

Optimization of Process Parameters and Microscopic Morphology of Multi-Walled Carbon Nanotubes/PEEK Films Using the Vacuum Suction Filtration Method

by Mingyu Liu, Hongya Fu, Songsong Yu, Ziang Jin, Zhenyu Han and Shouzheng Sun

Crystals 2024, 14(6), 561; https://doi.org/10.3390/cryst14060561 - 17 Jun 2024

Viewed by 392

Abstract

Multi-walled carbon nanotubes (MWCNTs) are a high-quality interlamination reinforcement material, but the high viscosity of polyetheretherketone (PEEK) prevents good fusion between MWCNTs and PEEK. This study proposes a method to achieve the complete integration of MWCNTs and PEEK through the preparation of a [...] Read more.

Multi-walled carbon nanotubes (MWCNTs) are a high-quality interlamination reinforcement material, but the high viscosity of polyetheretherketone (PEEK) prevents good fusion between MWCNTs and PEEK. This study proposes a method to achieve the complete integration of MWCNTs and PEEK through the preparation of a composite film using the vacuum suction filtration (VSF) method and optimizes the process parameters. An orthogonal experiment with three factors (filter paper pore size, ultrasonic dispersion time, and PEEK content) at three levels is designed, and mechanical performance testing and microscopic morphology observation are conducted. The influence of the three factors of filter paper pore size, ultrasonic time, and PEEK content on the elastic modulus and tensile strength of the film is investigated. The results are a filter paper pore size of 0.45 μm, ultrasonic time of 8.3 h, and PEEK content of 336.524 mg. The mechanical performance obtained under the optimal process parameters are an elastic modulus of 2437.5723 MPa and a tensile strength of 46.5196 MPa. This optimal process increases the elastic modulus by 12.3152% while maintaining a high tensile strength. Full article

(This article belongs to the Special Issue Recent Advances in the Mechanical Properties of Fiber Composite Materials)

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16 pages, 6322 KiB

Open AccessArticle

X-ray Single-Crystal Analysis, Pharmaco-Toxicological Profile and Enoyl-ACP Reductase-Inhibiting Activity of Leading Sulfonyl Hydrazone Derivatives

by Yoanna Teneva, Rumyana Simeonova, Orlin Besarboliev, Hristina Sbirkova-Dimitrova and Violina T. Angelova

Crystals 2024, 14(6), 560; https://doi.org/10.3390/cryst14060560 - 17 Jun 2024

Viewed by 382

Abstract

Taking into consideration the growing resistance towards currently available antimycobacterials, there is still an unmet need for the development of new chemotherapeutic agents to combat the infectious agents. This study presents X-ray single-crystal analysis to verify the structure of leading sulfonyl hydrazone 3b [...] Read more.

Taking into consideration the growing resistance towards currently available antimycobacterials, there is still an unmet need for the development of new chemotherapeutic agents to combat the infectious agents. This study presents X-ray single-crystal analysis to verify the structure of leading sulfonyl hydrazone 3b, which has proven its potent antimycobacterial activity against Mycobacterium tuberculosis H37Rv with an MIC value of 0.0716 μM, respectively, low cytotoxicity, and very high selectivity indexes (SI = 2216), and which has been fully characterized by Nuclear Magnetic Resonance (NMR) and High-Resolution Mass Spectrometry (HRMS) methods. Furthermore, this study assessed the ex vivo antioxidant activity, acute and subacute toxicity, and in vitro inhibition capacity against enoyl-ACP reductase of hydrazones 3a and 3b, as 3a was identified as the second leading compound in our previous research. Compared to isoniazid, compounds 3a and 3b demonstrated lower acute toxicity for intraperitoneal administration, with LD₅₀ values of 866 and 1224.7 mg/kg, respectively. Subacute toxicity tests, involving the repeated administration of a single dose of the test samples per day, revealed no significant deviations in hematological and biochemical parameters or pathomorphological tissues. The compounds exhibited potent antioxidant capabilities, reducing malondialdehyde (MDA) levels and increasing reduced glutathione (GSH). Enzyme inhibition assays of the sulfonyl hydrazones 3a and 3b with IC₅₀ values of 18.2 µM and 10.7 µM, respectively, revealed that enoyl acyl carrier protein reductase (InhA) could be considered as their target enzyme to exhibit their antitubercular activities. In conclusion, the investigated sulfonyl hydrazones display promising drug-like properties and warrant further investigation. Full article

(This article belongs to the Section Organic Crystalline Materials)

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9 pages, 5570 KiB

Open AccessArticle

Influence of Powder Size on Pore Characteristics and Intermetallic Phase Kinetics in Porous Ti-Al Alloys

by Saif Haider Kayani, Hafiz Muhammad Salman Ajmal, Byung-Joo Kim, Nho-Kwang Park and Kwangjun Euh

Crystals 2024, 14(6), 559; https://doi.org/10.3390/cryst14060559 - 17 Jun 2024

Viewed by 332

Abstract

This study investigates the impact of varying powder size on porosity, pore parameters, and intermetallic phase reaction during the reactive sintering of porous TiAl alloys. Ti52Al48 alloys were prepared using coarse (200 mesh) and fine (325 mesh) Ti powders through elemental powder metallurgy [...] Read more.

This study investigates the impact of varying powder size on porosity, pore parameters, and intermetallic phase reaction during the reactive sintering of porous TiAl alloys. Ti52Al48 alloys were prepared using coarse (200 mesh) and fine (325 mesh) Ti powders through elemental powder metallurgy and were subsequently sintered at different temperatures, 600 and 1200 °C. Our findings reveal a consistent pore morphology and intermetallic phase microstructure across both alloys. However, samples containing fine Ti powder exhibited a higher number density of small pores compared to those incorporating coarse Ti powders. Additionally, alloys prepared with fine Ti powders demonstrated a higher porosity than those prepared with coarse powders. Consequently, fine Ti powder promoted enhanced diffusion between Ti and Al during sintering, as reflected by the lower onset temperature and enthalpy of intermetallic reaction during sintering. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Behaviour of Structural Materials)

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23 pages, 30432 KiB

Open AccessArticle

Application of Organo-Modified Silica Nanoparticles to Improve the Load-Bearing Capacity of Bonded Joints of Dissimilar Steel Substrates

by Anna Guzanová, Dagmar Draganovská, Miroslav Tomáš, Petr Szelag, Nikita Veligotskyi, Miroslav Džupon and Marek Vojtko

Crystals 2024, 14(6), 558; https://doi.org/10.3390/cryst14060558 - 17 Jun 2024

Viewed by 514

Abstract

The paper deals with the joining of dissimilar steels by adhesive bonding. The base materials for the experimental work were deep-drawn low-carbon steel DC04, and hot-dip galvanized HSLA steel HX340LAD+Z. Adhesive bonding was performed using rubber-based and epoxy-based adhesives. The research aimed to [...] Read more.

The paper deals with the joining of dissimilar steels by adhesive bonding. The base materials for the experimental work were deep-drawn low-carbon steel DC04, and hot-dip galvanized HSLA steel HX340LAD+Z. Adhesive bonding was performed using rubber-based and epoxy-based adhesives. The research aimed to verify the importance of surface preparation of steel substrates using a formulation with organically modified silica nanoparticles and epoxy organic functional groups, where one end of the functional group can be incorporated into the organic binder of the coating material and the other end can be firmly bonded to substances of an inorganic nature (metals). Since the binder base of adhesives is very similar to that of coatings, verifying the performance of this surface preparation when interacting with the adhesive is necessary. The load-bearing tensile shear capacity of single-lapped joints and the resistance of the joints against corrosion-induced disbanding in a climate chamber were tested. The energy dissipated by the joints up to fracture was calculated from the load-displacement curves. Bonded joints with organosilane were compared with joints without surface preparation and joints prepared by chroman-free zirconate passivation treatment. Exposure of the joints in the climatic chamber did not cause a relevant reduction in the characteristics of the joints. Organosilicate formulation was proved effective when bonding ungalvanized steels with a rubber-based structural adhesive, where it improves the bond quality between the adhesive and the substrate. Full article

(This article belongs to the Special Issue Advanced Crystalline Materials, Mechanical Properties and Innovative Production Systems (2nd Edition))

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11 pages, 3082 KiB

Open AccessArticle

High Mechanical Property and Texture Degree of Hot-Extruded Bi_0.905Sb_0.095

by Linghao Zhao, Hongcheng Zhang, Degang Zhao, Dawei Wang, Ruiheng Liu and Jianghe Feng

Crystals 2024, 14(6), 557; https://doi.org/10.3390/cryst14060557 - 16 Jun 2024

Viewed by 580

Abstract

Bi_1−xSb_x crystal is one of the best n-type thermoelectric materials below 200 K, but its weak mechanical strength hinders practical applications for deep refrigeration. Herein, we adopted the mechanical enhancement method of hot extrusion to investigate the comprehensive mechanical and [...] Read more.

Bi_1−xSb_x crystal is one of the best n-type thermoelectric materials below 200 K, but its weak mechanical strength hinders practical applications for deep refrigeration. Herein, we adopted the mechanical enhancement method of hot extrusion to investigate the comprehensive mechanical and thermoelectric properties of Bi_0.905Sb_0.095. It revealed that reducing the grain size of the matrix and increasing the extrusion ratio can improve the gain size uniformity and mechanical properties. Meanwhile, the thermoelectric performance depends on the texture, grain size, and local composition. The extruded sample prepared by ingot with the high extrusion ratio of 9:1 generated uniform small grains, which resulted in the high bending strength of Bi_1−xSb_x~130 Mpa and a high power factor of ~68 μW·cm⁻¹·K⁻²@173 K, as well as the relatively high figure of merit of 0.25@173K. This work highlights the importance of the uniform distribution of the grain size and the compositions for Bi_1−xSb_x, as well as the required universal key parameter for the hot extrusion method. Full article

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

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28 pages, 11931 KiB

Open AccessArticle

Chloride-Induced Stress Corrosion Cracking of Friction Stir-Welded 304L Stainless Steel: Effect of Microstructure and Temperature

by Anirban Naskar, Madhumanti Bhattacharyya, Saumyadeep Jana, Jens Darsell, Krishnan S. Raja and Indrajit Charit

Crystals 2024, 14(6), 556; https://doi.org/10.3390/cryst14060556 - 16 Jun 2024

Viewed by 309

Abstract

Dry storage canisters of used nuclear fuels are fabricated using SUS 304L stainless steel. Chloride-induced stress corrosion cracking (CISCC) is one of the major failure modes of dry storage canisters. The cracked canisters can be repaired by friction stir welding (FSW), a low-heat [...] Read more.

Dry storage canisters of used nuclear fuels are fabricated using SUS 304L stainless steel. Chloride-induced stress corrosion cracking (CISCC) is one of the major failure modes of dry storage canisters. The cracked canisters can be repaired by friction stir welding (FSW), a low-heat input ‘solid-phase’ welding process. It is important to evaluate the ClSCC resistance of the friction stir welded material. Stress corrosion cracking (SCC) studies were carried out on mill-annealed base materials and friction stir welded 304L stainless U-bend specimens in 3.5% NaCl + 5 N H₂SO₄ solution at room temperature and boiling MgCl₂ solution at 155 °C. The engineering stress on the outer fiber of the FSW U-bend specimen was ~60% higher than that of the base metal (BM). In spite of the higher stress level of the FSW, both materials (FSW and BM) showed almost similar SCC failure times in the two different test solutions. The SCC occurred in the thermo-mechanically affected zone (TMAZ) of the FSW specimens in the 3.5% NaCl + 5 N H₂SO₄ solution at room temperature, while the stirred zone (SZ) was relatively crack-free. The failure occurred at the stirred zone when tested in the boiling MgCl₂ solution. Hydrogen reduction was the cathodic reaction in the boiling MgCl₂ solution, which promoted hydrogen-assisted cracking of the heavily deformed stirred zone. The emergence of the slip step followed by passive film rupture and dissolution of the slip step could be the SCC events in the 3.5% NaCl + 5 N H₂SO₄ solution at room temperature. However, the slip step height was not sufficient to cause passivity breakdown in the fine-grained SZ. Therefore, the SCC occurred in the partially recrystallized softer TMAZ. Overall, the friction-stirred 304L showed higher tolerance to ClSCC than the 304L base metal. Full article

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

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11 pages, 3270 KiB

Open AccessArticle

Synthesis, Structure and Magnetic Properties of Low-Dimensional Copper(II) trans-1,4-cyclohexanedicarboxylate

by Pavel A. Demakov, Anna A. Ovchinnikova, Pavel V. Dorovatovskii, Vladimir A. Lazarenko, Alexander N. Lavrov, Danil N. Dybtsev and Vladimir P. Fedin

Crystals 2024, 14(6), 555; https://doi.org/10.3390/cryst14060555 - 15 Jun 2024

Viewed by 396

Abstract

A reaction between copper(II) nitrate and trans-1,4-cyclohexanedicarboxylic acid (H₂chdc) carried out under hydrothermal conditions led to a new metal-organic coordination polymer [Cu₂(Hchdc)₂(chdc)]_n. According to single-crystal XRD data, the compound is based on bi-nuclear paddlewheel-type [...] Read more.

A reaction between copper(II) nitrate and trans-1,4-cyclohexanedicarboxylic acid (H₂chdc) carried out under hydrothermal conditions led to a new metal-organic coordination polymer [Cu₂(Hchdc)₂(chdc)]_n. According to single-crystal XRD data, the compound is based on bi-nuclear paddlewheel-type carboxylate blocks that are joined with polymeric chains due to the (μ₃-κ¹:κ²) coordination of carboxylate groups. The chains are interconnected by chdc²⁻ bridging ligands into layers containing free COOH groups of terminal Hchdc⁻. The neighboring layers adopt a RCOOH···OOCR hydrogen bond-assisted arrangement into a dense-packed structure. Magnetization measurements showed the presence of a strong antiferromagnetic exchange interaction (J/k_B = −495 K) inside the bi-nuclear blocks. At the same time, no significant interaction was found between the {-Cu₂(OOCR)₄-} units in spite of their polymeric in-chain packing. Patterns of magnetic behavior of [Cu₂(Hchdc)₂(chdc)]_n were thoroughly analyzed and explained from a structural point of view. Full article

(This article belongs to the Section Hybrid and Composite Crystalline Materials)

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21 pages, 5316 KiB

Open AccessArticle

Superlattice Symmetries Reveal Electronic Topological Transition in CaC₆ with Pressure

by Bruce Wang, Antonio Bianconi, Ian D. R. Mackinnon and Jose A. Alarco

Crystals 2024, 14(6), 554; https://doi.org/10.3390/cryst14060554 - 14 Jun 2024

Viewed by 779

Abstract

The electronic properties of calcium-intercalated graphite (CaC₆) as a function of pressure are revisited using density functional theory (DFT). The electronic band structures of CaC₆, like many other layered superconducting materials, display cosine-shaped bands at or near the Fermi [...] Read more.

The electronic properties of calcium-intercalated graphite (CaC₆) as a function of pressure are revisited using density functional theory (DFT). The electronic band structures of CaC₆, like many other layered superconducting materials, display cosine-shaped bands at or near the Fermi level (FL). Such bands encompass bonding/antibonding information with a strong connection to superconducting properties. Using a hexagonal cell representation for CaC₆, the construction of a double supercell in the c-direction effects six-folding in the reciprocal space of the full cosine function, explicitly revealing the bonding/antibonding relationship divide at the cosine midpoint. Similarly, folding of the Fermi surface (FS) reveals physical phenomena relevant to electronic topological transitions (ETTs) with the application of pressure. The ETT is characterised by a transition of open FS loops to closed loops as a function of pressure. As the highest transition temperature is reached with pressure, the dominant continuous, open FS loops shift to a different region of the FS. For CaC₆, the peak value for the superconducting transition temperature, T_c, occurs at about 7.5 GPa, near the observed pressure of the calculated ETT. At this pressure, the radius of the nearly spherical Ca 4s-orbital FS coincides with three times the distance from the Γ centre point to the Brillouin zone (BZ) boundary of the 2c supercell. In addition, the ETT coincides with the alignment of the nonbonding (inflection) point of the cosine band with the FL. At other calculated pressure conditions, the Ca 4s-orbital FS undergoes topological changes that correspond and can be correlated with experimentally determined changes in T_c. The ETT is a key mechanism that circumscribes the known significant drop in T_c for CaC₆ as a function of increasing pressure. Consistent calculated responses of the ETT to pressure match experimental measurements and validate the examination of superlattices as important criteria for understanding mechanisms driving superconductivity. Full article

(This article belongs to the Special Issue Computational and Theoretical Insights into Superconductors Advancements)

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13 pages, 5877 KiB

Open AccessArticle

Study of Leakage Current Transport Mechanisms in Pseudo-Vertical GaN-on-Silicon Schottky Diode Grown by Localized Epitaxy

by Mohammed El Amrani, Julien Buckley, Thomas Kaltsounis, David Plaza Arguello, Hala El Rammouz, Daniel Alquier and Matthew Charles

Crystals 2024, 14(6), 553; https://doi.org/10.3390/cryst14060553 - 14 Jun 2024

Viewed by 428

Abstract

In this work, a GaN-on-Si quasi-vertical Schottky diode was demonstrated on a locally grown n-GaN drift layer using Selective Area Growth (SAG). The diode achieved a current density of 2.5 kA/cm², a specific on-resistance

R_{O N, s p}

of [...] Read more.

In this work, a GaN-on-Si quasi-vertical Schottky diode was demonstrated on a locally grown n-GaN drift layer using Selective Area Growth (SAG). The diode achieved a current density of 2.5 kA/cm², a specific on-resistance

R_{O N, s p}

of 1.9 mΩ cm² despite the current crowding effect in quasi-vertical structures, and an on/off current ratio (I_on/I_off) of 10¹⁰. Temperature-dependent current–voltage characteristics were measured in the range of 313–433 K to investigate the mechanisms of leakage conduction in the device. At near-zero bias, thermionic emission (TE) was found to dominate. By increasing up to 10 V, electrons gained enough energy to excite into trap states, leading to the dominance of Frenkel–Poole emission (FPE). For a higher voltage range (−10 V to −40 V), the increased electric field facilitated the hopping of electrons along the continuum threading dislocations in the “bulk” GaN layers, and thus, variable range hopping became the main mechanism for the whole temperature range. This work provides an in-depth insight into the leakage conduction transport on pseudo-vertical GaN-on-Si Schottky barrier diodes (SBDs) grown by localized epitaxy. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor: GaN and SiC Material and Device)

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21 pages, 11142 KiB

Open AccessReview

Recent Progress of Floating-Zone Techniques for Bulk Single-Crystal Growth

by Naoki Kikugawa

Crystals 2024, 14(6), 552; https://doi.org/10.3390/cryst14060552 - 14 Jun 2024

Viewed by 688

Abstract

This review describes the recent progress of floating-zone techniques for bulk single-crystal growth. The most crucial point of the crucible-free technique is to keep the molten zone stable. It has been investigated and reported to yield a steeper temperature gradient at the liquid–solid [...] Read more.

This review describes the recent progress of floating-zone techniques for bulk single-crystal growth. The most crucial point of the crucible-free technique is to keep the molten zone stable. It has been investigated and reported to yield a steeper temperature gradient at the liquid–solid interface along the growth direction and a homogeneous molten liquid along the rotation axis. This article overviews several recent achievements starting from the conventional setup, particularly for lamps equipped in horizontal or vertical configurations, tilting mirrors, shielding the irradiation, and filament sizes for the optical-lamp floating-zone furnaces. Also, the recently advancing laser-heated floating-zone furnaces are described. Throughout the article, the author emphasizes that the floating-zone technique has been a powerful tool for crystal growth since the 1950s with its roots in the zone-melting method, and it has still been advancing for further materials’ growth such as quantum materials with modern scientific concepts. Full article

(This article belongs to the Special Issue Advances in Crystal Growth: Pioneering Materials for Tomorrow's Technologies)

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13 pages, 2173 KiB

Open AccessArticle

Abundant Catalytic Edge Sites in Few-Layer Horizontally Aligned MoS₂ Nanosheets Grown by Space-Confined Chemical Vapor Deposition

by Alin Velea, Angel-Theodor Buruiana, Claudia Mihai, Elena Matei, Teddy Tite and Florinel Sava

Crystals 2024, 14(6), 551; https://doi.org/10.3390/cryst14060551 - 14 Jun 2024

Viewed by 481

Abstract

Recently, a smart strategy for two-dimensional (2D) materials synthesis has emerged, namely space-confined chemical vapor deposition (CVD). Its extreme case is the microreactor method, in which the growth substrate is face-to-face stacked on the source substrate. In order to grow 2D transition metal [...] Read more.

Recently, a smart strategy for two-dimensional (2D) materials synthesis has emerged, namely space-confined chemical vapor deposition (CVD). Its extreme case is the microreactor method, in which the growth substrate is face-to-face stacked on the source substrate. In order to grow 2D transition metal dichalcogenides by this method, transition metal oxides, dispersed in very small amounts on the source substrate, are used as source materials in most of the published reports. In this paper, a colloidal dispersion of MoS₂ in saline solution is used and MoS₂ nanosheets with various shapes, sizes (between 5 and 60 μm) and thicknesses (2–4 layers) have been synthesized. Small MoS₂ flakes (regular or defective) are present on the surface of the nanosheets. Catalytic sites, undercoordinated atoms located at the edges of MoS₂ flakes and nanosheets, are produced in a high number by a layer-plus-island (Stranski–Krastanov) growth mechanism. Several double-resonance Raman bands (at 147, 177, 187, 225, 247, 375 cm⁻¹) are assignable to single phonon processes in which the excited electron is elastically scattered on a defect. The narrow 247 cm⁻¹ peak is identified as a topological defect-activated peak. These findings highlight the potential of defect engineering in material property optimization, particularly for solar water splitting applications. Full article

(This article belongs to the Special Issue Advanced Materials for Applications in Water Splitting)

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19 pages, 12474 KiB

Open AccessArticle

Unveiling the Synthesis of Strontium Ferrites by Sol-Gel and Laser Floating Zone Methods for Energy Application

by Silvia Soreto Teixeira, Rafael Ferreira, João Carvalho and Nuno M. Ferreira

Crystals 2024, 14(6), 550; https://doi.org/10.3390/cryst14060550 - 13 Jun 2024

Viewed by 349

Abstract

This work proposes the synthesis of strontium ferrite by two different methods: sol-gel (SG), using powdered coconut water (PCW) as a precursor, and laser floating zone (LFZ). The SG samples were after treated at temperatures of 700, 1000, and 1200 °C, while the [...] Read more.

This work proposes the synthesis of strontium ferrite by two different methods: sol-gel (SG), using powdered coconut water (PCW) as a precursor, and laser floating zone (LFZ). The SG samples were after treated at temperatures of 700, 1000, and 1200 °C, while the samples obtained by LFZ were grown at pulling rates of 10, 50, and 100 mm/h. All samples studied were subjected to structural characterization techniques, as well as electrical (AC and DC) and magnetic characterization. Through X-ray diffraction, it was possible to observe that all the samples presented strontium ferrites, but none were single phase. The phases detected in XRD were confirmed by Raman spectroscopy. Scanning electron micrography allowed the observation of an increase in grain size with the temperature of SG samples and the reduction of the porosity with the decrease in growth rate for LFZ fibers. Through electrical analysis, it was observed that the most suitable samples for energy storage were the samples grown at 100 mm/h (

ε_{r}^{'}

= 430,712;

ε_{r}^{″}

= 11,577; tan

δ

= 0.84; σ_ac = 0.0006 S/m, at 1 kHz). The remaining samples had high dielectric losses and can be applied in electromagnetic shielding. The SG 700 °C sample presented the highest magnetization (38.5 emu/g at T = 5 K). Full article

(This article belongs to the Special Issue Advanced Research of Electroceramics for Energy Conversion, Storage and Devices)

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9 pages, 9146 KiB

Open AccessArticle

The Temperature-Dependent Thermal Conductivity of C- and O-Doped Si₃N₄: First-Principles Calculations

by Hongfei Shao, Jiahao Qiu, Xia Liu, Xuejun Hou and Jinyong Zhang

Crystals 2024, 14(6), 549; https://doi.org/10.3390/cryst14060549 - 13 Jun 2024

Viewed by 351

Abstract

Silicon nitride (Si₃N₄) possesses excellent mechanical properties and high thermal conductivity, which is an important feature in many applications. However, achieving the theoretically high thermal conductivity of Si₃N₄ in practice is challenging. In this study, we [...] Read more.

Silicon nitride (Si₃N₄) possesses excellent mechanical properties and high thermal conductivity, which is an important feature in many applications. However, achieving the theoretically high thermal conductivity of Si₃N₄ in practice is challenging. In this study, we adopted a first-principles calculation method to assess the effects of doping β-Si₃N₄ and γ-Si₃N₄ with carbon and oxygen atoms. Applying geometric structure optimization combined with calculation of the electronic phonon properties generated a stable doped structure. The results revealed that carbon and oxygen doping have little effect on the Si₃N₄ unit cell size, but that oxygen doping increases the unit cell volume. Energy band structure and state density calculation results showed that carbon doping reduces the nitride band gap width, whereas oxygen doping results in an n-type Si₃N₄ semiconductor. The findings from this study are significant in establishing a basis for targeted increase of the thermal conductivity of Si₃N₄. Full article

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

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13 pages, 2542 KiB

Open AccessArticle

Lactonization of α-Ferrocenyl Ketocarboxylic Acids via Nucleophilic Attack of Carbonyl Oxygen

by Uttam R. Pokharel, Brennan J. Curole, Autumn M. Andras, Brandon P. LeBlanc and Frank R. Fronczek

Crystals 2024, 14(6), 548; https://doi.org/10.3390/cryst14060548 - 12 Jun 2024

Viewed by 552

Abstract

The effects of the ferrocenyl moiety to enhance the nucleophilicity of the carbonyl group, situated at its adjacent position, have been explored in a series of α-ferrocenyl ketocarboxylic acids. In the presence of trifluoroacetic anhydride, 3-ferrocenoylpropionic acid and 4-ferrocenoylbutyric acid gave 5-ferrocenyl-4-trifluoroacetyl-2(3H [...] Read more.

The effects of the ferrocenyl moiety to enhance the nucleophilicity of the carbonyl group, situated at its adjacent position, have been explored in a series of α-ferrocenyl ketocarboxylic acids. In the presence of trifluoroacetic anhydride, 3-ferrocenoylpropionic acid and 4-ferrocenoylbutyric acid gave 5-ferrocenyl-4-trifluoroacetyl-2(3H)-furanone and 6-ferrocenyl-5-trifluoroacetyl-3,4-dihydropyran-2-one, respectively. Under similar reaction conditions, 2-ferrocenylcarbonylbenzoic acid, a keto carboxylic acid without a β-hydrogen, gave a dimerized lactone, 3,3′-diferrocenyl-3,3′-diphthalide, possibly due to radical coupling. The nucleophilic attack of carbonyl oxygen, activated by the ferrocenyl moiety, on the carboxylic carbon is assumed to be the crucial mechanistic step in forming these lactones. When the carbonyl group was reduced to an alcohol to break its conjugation with the ferrocenyl moiety, saturated lactones were isolated after the acidic workup. These results indicate that the α-ferrocenyl carbinols readily undergo solvolysis under acidic conditions, giving ferrocenylcarbenium ions, which are attacked by the carboxy oxygen to give lactones. Full article

(This article belongs to the Special Issue Coordination Complexes: Synthesis, Characterization and Application)

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12 pages, 2070 KiB

Open AccessArticle

Investigations on the Carrier Mobility of Cs₂NaFeCl₆ Double Perovskites

by Jiyuan Xing, Yiting Zhao, Wei-Yan Cong, Chengbo Guan, Zhongchen Wu, Dong Liu and Ying-Bo Lu

Crystals 2024, 14(6), 547; https://doi.org/10.3390/cryst14060547 - 12 Jun 2024

Viewed by 353

Abstract

Double perovskite materials have gradually become widely studied due to their potential applications in solar cells and other optoelectronic devices. We take Cs₂NaFeCl₆ as an example to investigate the carrier mobility with respect to the acoustic phonon and the optical [...] Read more.

Double perovskite materials have gradually become widely studied due to their potential applications in solar cells and other optoelectronic devices. We take Cs₂NaFeCl₆ as an example to investigate the carrier mobility with respect to the acoustic phonon and the optical phonon scattering mechanisms. By considering the deformation potential, carrier effective mass, and bulk modulus, the longitudinal acoustic (LA) phonon-determined mobilities for electrons and holes in Cs₂NaFeCl₆ are found to be μ_e = 2886.08 cm² v⁻¹ s⁻¹ and μ_h = 39.09 cm² v⁻¹ s⁻¹, respectively. The optical scattering mechanism involves calculating the Fröhlich coupling constant, dielectric constant, and polaron mass to determine the multiple polar optical (PO) phonon-scattering-determined mobilities, resulting in μ_e = 279.25 cm² v⁻¹ s⁻¹ and μ_h = 21.29 cm² v⁻¹ s⁻¹, respectively. By combining both interactions, the total electron mobility and hole mobility are determined to be 254.61 cm² v⁻¹ s⁻¹ and 13.78 cm² v⁻¹ s⁻¹, respectively. The findings suggest that the polarization of both electrons and ions, small coupling constant, and bulk modulus in Cs₂NaFeCl₆’s lattice make PO scattering a significant contribution to carrier mobility in this specific double perovskite, highlighting the importance of considering this in enhancing the optoelectronic properties of Cs₂NaFeCl₆ and other double perovskites. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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