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A Themed Issue in Honour of Professor Alexandra Navrotsky on the Occasion of Her 80th Birthday

A special issue of Solids (ISSN 2673-6497).

Deadline for manuscript submissions: closed (30 June 2024) | Viewed by 13848

Special Issue Editor


E-Mail Website1 Website2
Guest Editor
CIRIMAT (Centre InterUniversitaire de Recherche et d’Ingénierie des Matériaux), Université de Toulouse 3 Paul Sabatier, CNRS, UPS, INP, 31062 Toulouse Cedex 9, France
Interests: ceramics; sintering; 3D shaping; capacitors; substrate; electronics & power electronics; environment

Special Issue Information

Dear Colleagues,

This special issue of Solids celebrates the accomplishment of Professor Alexandra Navrotsky on the occasion of her 80th birthday, for her long and outstanding career. Alexandra has made major contributions to both mineralogy/geochemistry and to solid state chemistry/materials science in the fields of ceramics, mantle mineralogy and deep earth geophysics, melt and glass science, nanomaterials and porous materials.

Alexandra was educated at the Bronx High School of Science and received her B.S., M.S. and Ph.D. in Physical Chemistry from the University of Chicago. After postdoctoral work in Germany and at Penn State University, she joined the faculty of Chemistry at Arizona State University, where she remained until her move to the Department of Geological and Geophysical Sciences at Princeton University in 1985. She chaired that department from 1988 to 1991 and was active at the Princeton Materials Institute. In 1997, she became an interdisciplinary Professor of Ceramic, Earth and Environment Materials Chemistry at the University of California at Davis and was appointed Edward Roessler Chair in Mathematical and Physical Sciences in 2001. She served as interim Dean of Mathematical and Physical Sciences, College of Letters and Science, UC Davis from 2013 to 2017. She organized the NEAT (Nano and New Materials in Energy, the Environment, Agriculture, and Technology) research group in 2002 and has directed the Peter A. Rock Thermochemistry Laboratory since her arrival in 1997. In 2019, Alexandra moved back to Arizona State University as a Professor and Regents Professor (since 2022) in the School of Molecular Sciences and the School for Engineering of Matter, Transport and Energy at ASU. She is also the Director of the Navrotsky Eyring Center for Materials of the Universe.

Alexandra's research interests have centered on relating microscopic features of structure and bonding to macroscopic thermodynamic behavior in minerals, ceramics, and other complex materials. Since 1997, Alexandra has designed, enhanced and built a unique high-temperature calorimetry facility. She introduced and applied the method for measuring the energetics of numerous materials, which provides insight into chemical bounding, order-disorder reactions, and phase transitions.

Throughout her exceptional career, Alexandra has always collaborated with scientists from all over the world. She has published over 1100 publications and her h factor = 87 testifies her celebrity and her huge contribution in many fields.

As acknowledgment of her outstanding contributions, Alexandra has received tremendous honors including an Alfred P. Sloan Fellowship (1973); Mineralogical Society of America Award (1981); American Geophysical Union Fellow (1988); Vice-President, Mineralogical Society of America (1991–1992), President (1992–1993); Geochemical Society Fellow (1997). She spent five years (1986–1991) as Editor, Physics and Chemistry of Minerals, and serves on numerous advisory committees and panels in both government and academy. She was elected to the National Academy of Sciences in 1993. In 1995 she received the Ross Coffin Purdy Award from the American Ceramic Society and was awarded the degree of Doctor Honoris Causa from Uppsala University, Sweden. In 2002 she was awarded the Benjamin Franklin Medal in Earth Science. In 2004, she was elected a Fellow of The Mineralogical Society (Great Britain) and awarded the Urey Medal (the highest career honor of the European Association of Geochemistry). In 2005, she received the Spriggs Phase Equilibria Award. In 2006, she received the Harry H. Hess Medal of the American Geophysical Union. In October 2009, she received the Roebling Medal (the highest honor of the Mineralogical Society of America). In 2011, she became a member of the American Philosophical Society. In 2016 she received the Victor M. Goldschmidt Award from the Geochemical Society and the W. David Kingery Award from the American Ceramic Society. The World Academy of Ceramics elected Prof. Navrotsky to Science Professional Member in 2017.

Recently, a newly discovered mineral K2Na10(UO2)3(SO4)9•2H2O was named Navrotskyite in her honor.

On the occasion of her 80th birthday we are delighted to have compiled in this Special Issue of Solids contributions from friends and colleagues from all over the world, covering a wide range of areas.

This compilation is the witness of the gratitude and the great honor to have work with Alexandra, and the inspiration she is for many scientists.

The aim of the special issue is to put together articles from the biomineralization, geochemistry, mineralogy and materials community that show new achievements, and moving steps towards understanding of the structure and stability of nanomaterials along with their dependance of temperature and pressure, the energy of phase transformation, etc.

In this Special Issue, original research articles and reviews are welcome. We look forward to receiving your contributions in the different fields mentioned above including, but not limited to:

  • Phase structure and stability;
  • Energy and transformation in complex systems;
  • Surfaces and interfaces;
  • Experimental Thermodynamics;
  • Energetics of nanomaterials.

Prof. Dr. Sophie Guillemet-Fritsch
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Solids is an international peer-reviewed open access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • energetics
  • phase transformation
  • complex system
  • solids
  • surfaces
  • interfaces
  • experimental thermodynamics

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Published Papers (12 papers)

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Research

19 pages, 3927 KiB  
Article
Kinetics of γ-LiAlO2 Formation out of Li2O-Al2O3 Melt—A Molecular Dynamics-Informed Non-Equilibrium Thermodynamic Study
by Sanchita Chakrabarty, Danilo Alencar De Abreu, Iyad Alabd Alhafez, Olga Fabrichnaya, Nina Merkert, Alena Schnickmann, Thomas Schirmer, Ursula E. A. Fittschen and Michael Fischlschweiger
Solids 2024, 5(4), 561-579; https://doi.org/10.3390/solids5040038 - 12 Nov 2024
Viewed by 449
Abstract
Slags generated from pyrometallurgical processing of spent Li-ion batteries are reservoirs of Li compounds that, on recycling, can reintegrate Li into the material stream. In this context, γ-LiAlO2 is a promising candidate that potentially increases recycling efficiency due to its high Li [...] Read more.
Slags generated from pyrometallurgical processing of spent Li-ion batteries are reservoirs of Li compounds that, on recycling, can reintegrate Li into the material stream. In this context, γ-LiAlO2 is a promising candidate that potentially increases recycling efficiency due to its high Li content and favorable morphology for separation. However, its solidification kinetics depends on melt compositions and cooling strategies. The Engineered Artificial Minerals approach aims to optimize process conditions that maximize the desired solid phases. To realize this goal, understanding the coupled influence of external cooling kinetics and internal kinetics of solid/liquid interface migration and mass and thermal diffusion on solidification is critical. In this work, the solidification of γ-LiAlO2 from a Li2O-Al2O3 melt is computationally investigated by applying a non-equilibrium thermodynamic model to understand the influence of varying processing conditions on crystallization kinetics. A strategy is illustrated that allows the effective utilization of thermodynamic information obtained by the CALPHAD approach and molecular dynamics-generated diffusion coefficients to simulate kinetic-dependent solidification. Model calculations revealed that melts with compositions close to γ-LiAlO2 remain comparatively unaffected by the external heat extraction strategies due to rapid internal kinetic processes. Kinetic limitations, especially diffusion, become significant for high cooling rates as the melt composition deviates from the stoichiometric compound. Full article
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12 pages, 3213 KiB  
Article
Pressure-Induced YbFe2O4-Type to Spinel Structural Change of InGaMgO4
by Takehiro Koike, Hena Das, Kengo Oka, Yoshihiro Kusano, Fernando Cubillas, Francisco Brown Bojorqez, Victor Emmanuel Alvarez-Montano, Shigekazu Ito, Kei Shigematsu, Hayato Togano, Ikuya Yamada, Hiroki Ishibashi, Yoshiki Kubota, Shigeo Mori, Noboru Kimizuka and Masaki Azuma
Solids 2024, 5(3), 422-433; https://doi.org/10.3390/solids5030028 - 19 Aug 2024
Viewed by 847
Abstract
Spinel-type InGaMgO4 with a = 8.56615(3) Å was prepared by treating layered YbFe2O4-type InGaMgO4 at 6 GPa and 1473 K. DFT calculation and Rietveld analysis of synchrotron X-ray powder diffraction data revealed the inverse spinel structure with [...] Read more.
Spinel-type InGaMgO4 with a = 8.56615(3) Å was prepared by treating layered YbFe2O4-type InGaMgO4 at 6 GPa and 1473 K. DFT calculation and Rietveld analysis of synchrotron X-ray powder diffraction data revealed the inverse spinel structure with In3+:Ga3+/Mg2+ = 0.726:0.274 in the tetrahedral site and 0.137:0.863 in the octahedral site. InGaMgO4 spinel is an insulator with an experimental band gap of 2.80 eV, and the attempt at hole doping by post-annealing in a reducing atmosphere to introduce an oxygen defect was unsuccessful. This is the first report of the bulk synthesis of AB2O4 compounds with both YbFe2O4 and spinel polymorphs. Full article
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18 pages, 4363 KiB  
Article
Point-Defect Segregation and Space-Charge Potentials at the Σ5(310)[001] Grain Boundary in Ceria
by Adrian L. Usler, Henrik J. Heelweg, Roger A. De Souza and Annalena R. Genreith-Schriever
Solids 2024, 5(3), 404-421; https://doi.org/10.3390/solids5030027 - 3 Aug 2024
Viewed by 944
Abstract
The atomistic structure and point-defect thermodynamics of the model Σ5(310)[001] grain boundary in CeO2 were explored with atomistic simulations. An interface with a double-diamond-shaped structural repeat unit was found to have the lowest energy. Segregation [...] Read more.
The atomistic structure and point-defect thermodynamics of the model Σ5(310)[001] grain boundary in CeO2 were explored with atomistic simulations. An interface with a double-diamond-shaped structural repeat unit was found to have the lowest energy. Segregation energies were calculated for oxygen vacancies, electron polarons, gadolinium and scandium acceptor cations, and tantalum donor cations. These energies deviate strongly from their bulk values over the same length scale, thus indicating a structural grain-boundary width of approximately 1.5 nm. However, an analysis revealed no unambiguous correlation between segregation energies and local structural descriptors, such as interatomic distance or coordination number. From the segregation energies, the grain-boundary space-charge potential in Gouy–Chapman and restricted-equilibrium regimes was calculated as a function of temperature for dilute solutions of (i) oxygen vacancies and acceptor cations and (ii) electron polarons and donor cations. For the latter, the space-charge potential is predicted to change from negative to positive in the restricted-equilibrium regime. For the former, the calculation of the space-charge potential from atomistic segregation energies is shown to require the inclusion of the segregation energies for acceptor cations. Nevertheless, the space-charge potential in the restricted-equilibrium regime can be described well with an empirical model employing a single effective oxygen-vacancy segregation energy. Full article
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10 pages, 2000 KiB  
Article
Synthesis and Crystal Structure of Ilmenite-Type Silicate with Pyrope Composition
by Takayuki Ishii, Ryosuke Sinmyo and Tomoo Katsura
Solids 2024, 5(3), 394-403; https://doi.org/10.3390/solids5030026 - 2 Aug 2024
Viewed by 846
Abstract
Akimotoite, ilmenite-type MgSiO3 high-pressure polymorph can be stable in the lower-mantle transition zone along average mantle and subducting slab geotherms. Significant amounts of Al2O3 can be incorporated into the structure, having the pyrope (Mg3Al2Si3 [...] Read more.
Akimotoite, ilmenite-type MgSiO3 high-pressure polymorph can be stable in the lower-mantle transition zone along average mantle and subducting slab geotherms. Significant amounts of Al2O3 can be incorporated into the structure, having the pyrope (Mg3Al2Si3O12) composition. Previous studies have investigated the effect of Al2O3 on its crystal structure at nearly endmember compositions. In this study, we synthesized high-quality ilmenite-type Mg3Al2Si3O12 phase at 27 GPa and 1073 K by means of a Kawai-type multi-anvil press and refined the crystal structure at ambient conditions using a synchrotron X-ray diffraction data via the Rietveld method to examine the effect of Al2O3. The unit-cell lattice parameters were determined to be a = 4.7553(7) Å, c = 13.310(2) Å, and V = 260.66(6) Å3, with Z = 6 (hexagonal, R3¯). The volume of the present phase was placed on the akimotoite-corundum endmember join. However, the refined structure showed a strong nonlinear behavior of the a- and c-axes, which can be explained by Al incorporation into the MgO6 and SiO6 octahedral sites, which are distinctly different each other. Ilmenite-type Mg3Al2Si3O12 phase may be found in shocked meteorites and can be a good indicator for shock conditions at relatively low temperatures of 1027–1127 K. Full article
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20 pages, 7850 KiB  
Article
Study of the Structure of Zn and Na Borophosphate Glasses Using X-ray and Neutron Scattering Techniques
by Uwe Hoppe, Parker T. Freudenberger, Richard K. Brow, Jozef Bednarčik and Alex C. Hannon
Solids 2024, 5(3), 355-374; https://doi.org/10.3390/solids5030024 - 1 Jul 2024
Viewed by 782
Abstract
The atomic structures of Zn and Na borophosphate glasses were studied using X-ray and neutron scattering techniques. Peaks assigned to the B−O, P−O, and O−O distances confirm that only BO4 units co-exist with the PO4 tetrahedra. The Zn−O and Na−O coordination [...] Read more.
The atomic structures of Zn and Na borophosphate glasses were studied using X-ray and neutron scattering techniques. Peaks assigned to the B−O, P−O, and O−O distances confirm that only BO4 units co-exist with the PO4 tetrahedra. The Zn−O and Na−O coordination numbers are found to be a little larger than four. The narrowest peaks of the Zn−O first-neighbor distances exist for the glasses along a line connecting the Zn(PO3)2 and BPO4 compositions (50 mol% P2O5), which is explained by networks of ZnO4, BO4, and PO4 tetrahedra with twofold coordinated oxygens. The calculated amounts of available oxygen support this interpretation. Broadened peaks occur for glasses with lower P2O5 contents, which is consistent with the presence of threefold coordinated oxygens. The two distinct P−O peak components of the Zn and Na borophosphate glasses differ in their relative abundances. This is interpreted as follows: Na+ cations coordinate oxygens in some P−O−B bridges, which is something not seen for the Zn2+ ions. Full article
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8 pages, 2732 KiB  
Article
High-Pressure Synthesis of the Iodide Carbonate Na5(CO3)2I
by Yuqing Yin, Leonid Dubrovinsky, Andrey Aslandukov, Alena Aslandukova, Fariia Iasmin Akbar, Wenju Zhou, Michael Hanfland, Igor A. Abrikosov and Natalia Dubrovinskaia
Solids 2024, 5(2), 333-340; https://doi.org/10.3390/solids5020022 - 18 Jun 2024
Viewed by 953
Abstract
Here, we present the synthesis of a novel quaternary compound, iodide carbonate Na5(CO3)2I, at 18(1) and 25.1(5) GPa in laser-heated diamond anvil cells. Single-crystal synchrotron X-ray diffraction provides accurate structural data for Na5(CO3) [...] Read more.
Here, we present the synthesis of a novel quaternary compound, iodide carbonate Na5(CO3)2I, at 18(1) and 25.1(5) GPa in laser-heated diamond anvil cells. Single-crystal synchrotron X-ray diffraction provides accurate structural data for Na5(CO3)2I and shows that the structure of the material can be described as built of INa8 square prisms, distorted NaO6 octahedra, and trigonal planar CO32− units. Decompression experiments show that the novel iodide carbonate is recoverable in the N2 atmosphere to ambient conditions. Our ab initio calculations agree well with the experimental structural data, provide the equation of state, and shed light on the chemical bonding and electronic properties of the new compound. Full article
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18 pages, 6373 KiB  
Article
Critical Experiments and Thermodynamic Modeling of the Li2O-SiO2 System
by Danilo Alencar de Abreu and Olga Fabrichnaya
Solids 2024, 5(2), 303-320; https://doi.org/10.3390/solids5020020 - 1 Jun 2024
Cited by 1 | Viewed by 860
Abstract
Phase equilibria studies were performed in the Li2O-SiO2 system for heat-treated samples using Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD). The temperature of the eutectic reaction (Liq. ⇌ Li4SiO4 + Li2SiO3) was [...] Read more.
Phase equilibria studies were performed in the Li2O-SiO2 system for heat-treated samples using Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD). The temperature of the eutectic reaction (Liq. ⇌ Li4SiO4 + Li2SiO3) was experimentally determined at 1289 K using Differential Thermal Analysis (DTA). No evidences of the Li6Si2O7 formation was found by the experimental investigation and therefore, it was not considered. Heat capacity of the Li8SiO6 phase was measured using Differential Scanning Calorimetry (DSC). Solid phases of the Li2O-SiO2 system were described as stoichiometric compounds and liquid phases by two-sublattice partially ionic liquid model. Four stoichiometric intermediate compounds were considered to be stable (Li8SiO6, Li4SiO4, Li2SiO3 and Li2Si2O5). The polymorphic transformation in Li2Si2O5 phase was accounted and the metastable liquid miscibility gap on SiO2-rich side was reproduced. The calculated phase diagram satisfactorily agrees with the experimental phase equilibria as well as calculated thermodynamic properties reproduces experimental values within uncertainty limits. Full article
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13 pages, 6456 KiB  
Article
Uncovering the Effects of Non-Hydrostaticity on Pressure-Induced Phase Transformation in Xenotime-Structured TbPO4
by Jai Sharma and Corinne E. Packard
Solids 2024, 5(1), 110-122; https://doi.org/10.3390/solids5010008 - 16 Feb 2024
Cited by 1 | Viewed by 879
Abstract
The pressure-induced phase transformations of rare earth orthophosphates (REPO4s) have become increasingly relevant in ceramic matrix composite (CMC) research; however, understanding of the shear-dependence of these transformations remains limited. This study employs diamond anvil cell experiments with three pressure media (neon, [...] Read more.
The pressure-induced phase transformations of rare earth orthophosphates (REPO4s) have become increasingly relevant in ceramic matrix composite (CMC) research; however, understanding of the shear-dependence of these transformations remains limited. This study employs diamond anvil cell experiments with three pressure media (neon, KCl, sample itself/no medium) to systematically assess the effect of shear on the phase transformations of TbPO4. Results show a lowering of the TbPO4 transformation onset pressure (Ponset) as well as an extension of the xenotime–monazite phase coexistence range under non-hydrostatic conditions. The TbPO4 Ponset under no medium (4.4(3) GPa) is the lowest REPO4 Ponset reported to date and represents a ~50% drop from the hydrostatic Ponset. Enthalpic differences likely account for lower Ponset values in TbPO4 compared to DyPO4. Experiments also show scheelite may be the post-monazite phase of TbPO4; this phase is consistent with observed and predicted REPO4 transformation pathways. Full article
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12 pages, 4701 KiB  
Article
Synthesis and Crystal and Electronic Structures of the Zintl Phase Sr21Cd4Sb18
by Kowsik Ghosh and Svilen Bobev
Solids 2023, 4(4), 344-355; https://doi.org/10.3390/solids4040022 - 17 Nov 2023
Cited by 1 | Viewed by 1338
Abstract
Reported herein are the synthesis and crystal chemistry analysis of the Zintl phase Sr21Cd4Sb18. Single crystals of this compound were grown using the Sn-flux method, and structural characterization was carried out using single-crystal X-ray diffraction. Crystal data: [...] Read more.
Reported herein are the synthesis and crystal chemistry analysis of the Zintl phase Sr21Cd4Sb18. Single crystals of this compound were grown using the Sn-flux method, and structural characterization was carried out using single-crystal X-ray diffraction. Crystal data: Monoclinic space group C2/m (No. 12, Z = 4); a = 18.2536(6) Å, b = 17.4018(5) Å, and c = 17.8979(6) Å, β = 92.024(1)°. The structure is based on edge- and corner-shared CdSb4 tetrahedra, which ultimately form octameric [Cd8Sb22] fragments, where two symmetry-equivalent subunits are connected via a homoatomic Sb–Sb interaction. The electronic band structure calculations contained herein reveal the emergence of a direct gap between the valence and the conduction bands. Full article
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17 pages, 1498 KiB  
Article
Thermodynamic Properties as a Function of Temperature of AlMoNbV, NbTaTiV, NbTaTiZr, AlNbTaTiV, HfNbTaTiZr, and MoNbTaVW Refractory High-Entropy Alloys from First-Principles Calculations
by Danielsen E. Moreno and Chelsey Z. Hargather
Solids 2023, 4(4), 327-343; https://doi.org/10.3390/solids4040021 - 6 Nov 2023
Viewed by 1818
Abstract
Refractory high-entropy alloys (RHEAs) are strong candidates for use in high-temperature engineering applications. As such, the thermodynamic properties as a function of temperature for a variety of RHEA systems need to be studied. In the present work, thermodynamic quantities such as entropy, enthalpy, [...] Read more.
Refractory high-entropy alloys (RHEAs) are strong candidates for use in high-temperature engineering applications. As such, the thermodynamic properties as a function of temperature for a variety of RHEA systems need to be studied. In the present work, thermodynamic quantities such as entropy, enthalpy, heat capacity at constant volume, and linear thermal expansion are calculated for three quaternary and three quinary single-phase, BCC RHEAs: AlMoNbV, NbTaTiV, NbTaTiZr, AlNbTaTiV, HfNbTaTiZr, and MoNbTaVW. First-principle calculations based on density functional theory are used for the calculations, and special quasirandom structures (SQSs) are used to represent the random solid solution nature of the RHEAs. A code for the finite temperature thermodynamic properties using the Debye-Grüneisen model is written and employed. For the first time, the finite temperature thermodynamic properties of all 24 atomic configuration permutations of a quaternary RHEA are calculated. At most, 1.7% difference is found between the resulting properties as a function of atomic configuration, indicating that the atomic configuration of the SQS has little effect on the calculated thermodynamic properties. The behavior of thermodynamic properties among the RHEAs studied is discussed based on valence electron concentration and atomic size. Among the quaternary RHEAs studied, namely AlMoNbV, NbTaTiZr, and NbTaTiV, it is found that the presence of Zr contributes to higher entropy. Additionally, at lower temperatures, Zr contributes to higher heat capacity and thermal expansion compared to the alloys without Zr, possibly due to its valence electron concentration. At higher temperatures, Al contributes to higher heat capacity and thermal expansion, possibly due its ductility. Among the quinary systems, the presence of Mo, W, and/or V causes the RHEA to have a lower thermal expansion than the other systems studied. Finally, when comparing the systems with the NbTaTi core, the addition of Al increases thermal expansion, while the removal of Zr lowers the thermal expansion. Full article
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17 pages, 1894 KiB  
Article
Evaluating Phonon Characteristics by Varying the Layer and Interfacial Thickness in Novel Carbon-Based Strained-Layer Superlattices
by Devki N. Talwar and Piotr Becla
Solids 2023, 4(4), 287-303; https://doi.org/10.3390/solids4040018 - 1 Oct 2023
Cited by 1 | Viewed by 1230
Abstract
Systematic results of lattice dynamical calculations are reported as a function of m and n for the novel (SiC)m/(GeC)n superlattices (SLs) by exploiting a modified linear-chain model and a realistic rigid-ion model (RIM). A bond polarizability method is employed to [...] Read more.
Systematic results of lattice dynamical calculations are reported as a function of m and n for the novel (SiC)m/(GeC)n superlattices (SLs) by exploiting a modified linear-chain model and a realistic rigid-ion model (RIM). A bond polarizability method is employed to simulate the Raman intensity profiles (RIPs) for both the ideal and graded (SiC)10-Δ/(Si0.5Ge0.5C)Δ/(GeC)10-Δ/(Si0.5Ge0.5C)Δ SLs. We have adopted a virtual-crystal approximation for describing the interfacial layer thickness, Δ (≡0, 1, 2, and 3 monolayers (MLs)) by selecting equal proportions of SiC and GeC layers. Systematic variation of Δ has initiated considerable upward (downward) shifts of GeC-(SiC)-like Raman peaks in the optical phonon frequency regions. Our simulated results of RIPs in SiC/GeC SLs are agreed reasonably well with the recent analyses of Raman scattering data on graded short-period GaN/AlN SLs. Maximum changes in the calculated optical phonons (up to ±~47 cm−1) with Δ = 3, are proven effective for causing accidental degeneracies and instigating localization of atomic displacements at the transition regions of the SLs. Strong Δ-dependent enhancement of Raman intensity features in SiC/GeC are considered valuable for validating the interfacial constituents in other technologically important heterostructures. By incorporating RIM, we have also studied the phonon dispersions [ωjSLq] of (SiC)m/(GeC)n SLs along the growth [001] as well as in-plane [100], [110] directions [i.e., perpendicular to the growth]. In the acoustic mode regions, our results of ωjSLq  have confirmed the formation of mini-gaps at the zone center and zone edges while providing strong evidences of the anti-crossing and phonon confinements. Besides examining the angular dependence of zone-center optical modes, the results of phonon folding, confinement, and anisotropic behavior in (SiC)m/(GeC)n are compared and contrasted very well with the recent first-principles calculations of (GaN)m/(AlN)n strained layer SLs. Full article
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19 pages, 1307 KiB  
Article
Pressure-Dependent Crystal Radii
by Oliver Tschauner
Solids 2023, 4(3), 235-253; https://doi.org/10.3390/solids4030015 - 28 Aug 2023
Cited by 3 | Viewed by 1501
Abstract
This article reports the pressure-dependent crystal radii of Mg, Si, Ge, Be, Fe, Ca, Sr, Ba, Al, Ti, Li, Na, K, Cs, and of some rare earths, that is: the major Earth mantle elements, important minor, and some trace elements. Pressure dependencies of [...] Read more.
This article reports the pressure-dependent crystal radii of Mg, Si, Ge, Be, Fe, Ca, Sr, Ba, Al, Ti, Li, Na, K, Cs, and of some rare earths, that is: the major Earth mantle elements, important minor, and some trace elements. Pressure dependencies of O2−, Cl, and Br are also reported. It is shown that all examined cation radii vary linearly with pressure. Cation radii obey strict correlations between ionic compressibilities and reference 0 GPa radii, thus reducing previous empirical rules of the influence of valence, ion size, and coordination to a simple formula. Both cation and anion radii are functions of nuclear charge number and a screening function which for anions varies with pressure, and for cations is pressure-independent. The pressure derivative of cation radii and of the anion radii at high pressure depends on electronegativity with power −1.76. Full article
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