Pressure-Induced Phase Transformations (Volume II)

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Inorganic Crystalline Materials".

Deadline for manuscript submissions: closed (30 June 2023) | Viewed by 31808

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Special Issue Editors

Departamento de Física Aplicada-ICMUV, MALTA Consolider Team, Universidad de Valencia, 46010 València, Spain
Interests: high-pressure; phase transitions; oxides; X-ray diffraction; novel technological materials
Special Issues, Collections and Topics in MDPI journals
Departamento de Física Aplicada-ICMUV, MALTA Consolider Team, Universidad de Valencia, Valencia, Spain
Interests: solid state physics; high-pressure physics; phase transitions

Special Issue Information

Dear Colleagues,

The study of phase transitions in solids under high pressure and high temperature is a very active research field. In the last few decades, thanks to the development of experimental techniques and computer simulations, there have been many important discoveries. Many of the achievements made in recent years affect various research fields ranging from solid-state physics, chemistry, and materials science to geophysics. They not only involve the deepening of the knowledge on solid–solid phase transitions but also a better understanding of melting under compression. The impact of pressure on structural, chemical, and physical properties and several modern discoveries are the principal reasons for producing the current Special Issue.

This Special Issue on “Pressure-Induced Phase Transformations” aims to provide a forum for describing and discussing contemporary achievements. The goal is to give special emphasis to phase transitions and their effects on different physical properties, but other topics (especially melting studies) are not excluded. Authors are invited to contribute to the Special Issue with articles presenting new experimental and theoretical advances. Contributions discussing the relationships of phase transformations in solids under high pressure, the mechanism of these transformations, and their influence on physical and chemical properties are welcome.

Researchers working in a wide range of disciplines are invited to contribute to this Special Issue. The topics summarized under the keywords given below are only broad examples of the greater number of topics in mind. The volume is open not only to original manuscripts but also to feature and short review articles of current hot topics.

Prof. Dr. Daniel Errandonea
Dr. Enrico Bandiello
Guest Editors

Manuscript Submission Information

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Keywords

  • high pressure research
  • phase transitions
  • structural properties
  • transition mechanisms
  • equation of state
  • symmetry-breaking
  • melting curves

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Published Papers (20 papers)

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10 pages, 2031 KiB  
Article
High-Pressure Vibrational and Structural Studies of the Chemically Engineered Ferroelectric Phase of Sodium Niobate
by Sanjay Kumar Mishra, Nandini Garg, Smita Gohil, Ranjan Mittal and Samrath Lal Chaplot
Crystals 2023, 13(8), 1181; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst13081181 - 29 Jul 2023
Viewed by 825
Abstract
Pure NaNbO3 has an antiferroelectric phase at ambient pressure. The structural behaviour of the chemically engineered ferroelectric phase of sodium niobate, NNBT05: [(0.95) NaNbO3-(0.05) BaTiO3], under high-pressure has been studied using Raman scattering and angle-dispersive synchrotron X-ray diffraction [...] Read more.
Pure NaNbO3 has an antiferroelectric phase at ambient pressure. The structural behaviour of the chemically engineered ferroelectric phase of sodium niobate, NNBT05: [(0.95) NaNbO3-(0.05) BaTiO3], under high-pressure has been studied using Raman scattering and angle-dispersive synchrotron X-ray diffraction techniques. At pressure > 1 GPa, noticeable changes in the Raman spectra can be seen in the low wavenumber modes (150–300 cm−1). Large changes in the positions and intensities of the Raman bands as a function of pressure provide evidence for structural phase transition. The results indicate significant changes in the bond-lengths and the orientation of the NbO6 octahedra at ~1 GPa, and a transition to the paraelectric phase at ~5 GPa, which are at lower pressures than previously found in pure NaNbO3. The powder X-ray diffraction pattern shows an appreciable change in the peak profile in terms of position and width on increasing pressure. The pressure dependences of the structural parameters show that the response of the lattice parameters to pressure is strongly anisotropic. By fitting the pressure–volume data using the Birch–Murnaghan equation of state, the isothermal bulk modulus was estimated. The experimental results suggest that on doping BaTiO3 in NaNbO3, the bulk modulus increases. The bulk modulus of NNBT05 has been estimated to be 164.5 GPa, which is fairly close to 157.5 GPa, as previously observed in NaNbO3. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Volume II))
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11 pages, 2301 KiB  
Article
Pressure-Induced Structural Phase Transition of Co-Doped SnO2 Nanocrystals
by Vinod Panchal, Laura Pampillo, Sergio Ferrari, Vitaliy Bilovol, Catalin Popescu and Daniel Errandonea
Crystals 2023, 13(6), 900; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst13060900 - 31 May 2023
Cited by 1 | Viewed by 935
Abstract
Co-doped SnO2 nanocrystals (with a particle size of 10 nm) with a tetragonal rutile-type (space group P42/mnm) structure have been investigated for their use in in situ high-pressure synchrotron angle dispersive powder X-ray diffraction up to 20.9 [...] Read more.
Co-doped SnO2 nanocrystals (with a particle size of 10 nm) with a tetragonal rutile-type (space group P42/mnm) structure have been investigated for their use in in situ high-pressure synchrotron angle dispersive powder X-ray diffraction up to 20.9 GPa and at an ambient temperature. An analysis of experimental results based on Rietveld refinements suggests that rutile-type Co-doped SnO2 undergoes a structural phase transition at 14.2 GPa to an orthorhombic CaCl2-type phase (space group Pnnm), with no phase coexistence during the phase transition. No further phase transition is observed until 20.9 GPa, which is the highest pressure covered by the experiments. The low-pressure and high-pressure phases are related via a group/subgroup relationship. However, a discontinuous change in the unit-cell volume is detected at the phase transition; thus, the phase transition can be classified as a first-order type. Upon decompression, the transition has been found to be reversible. The results are compared with previous high-pressure studies on doped and un-doped SnO2. The compressibility of different phases will be discussed. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Volume II))
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21 pages, 4754 KiB  
Article
Theoretical Study of Pressure-Induced Phase Transitions in Sb2S3, Bi2S3, and Sb2Se3
by Estelina Lora da Silva, Mario C. Santos, Plácida Rodríguez-Hernández, Alfonso Muñoz and Francisco Javier Manjón
Crystals 2023, 13(3), 498; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst13030498 - 14 Mar 2023
Cited by 3 | Viewed by 1601
Abstract
We report an ab initio study of Sb2S3, Sb2Se3, and Bi2S3 sesquichalcogenides at hydrostatic pressures of up to 60 GPa. We explore the possibility that the C2/m, C2/c, the disordered [...] Read more.
We report an ab initio study of Sb2S3, Sb2Se3, and Bi2S3 sesquichalcogenides at hydrostatic pressures of up to 60 GPa. We explore the possibility that the C2/m, C2/c, the disordered Im-3m, and the I4/mmm phases observed in sesquichalcogenides with heavier cations, viz. Bi2Se3, Bi2Te3, and Sb2Te3, could also be formed in Sb2S3, Sb2Se3, and Bi2S3, as suggested from recent experiments. Our calculations show that the C2/c phase is not energetically favorable in any of the three compounds, up to 60 GPa. The C2/m system is also unfavorable for Sb2S3 and Bi2S3; however, it is energetically favorable with respect to the Pnma phase of Sb2Se3 above 10 GPa. Finally, the I4/mmm and the disordered body-centered cubic-type Im-3m structures are competitive in energy and are energetically more stable than the C2/m phase at pressures beyond 30 GPa. The dynamical stabilities of the Pnma, Im-3m, C2/m, and I4/mmm structural phases at high pressures are discussed for the three compounds. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Volume II))
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15 pages, 3447 KiB  
Article
Pressure-Induced Monoclinic to Tetragonal Phase Transition in RTaO4 (R = Nd, Sm): DFT-Based First Principles Studies
by Saheli Banerjee, Amit Tyagi and Alka B. Garg
Crystals 2023, 13(2), 254; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst13020254 - 01 Feb 2023
Cited by 2 | Viewed by 1285
Abstract
In this manuscript, we report the density functional theory-based first principles study of the structural and vibrational properties of technologically relevant M′ fergusonite (P2/c)-structured NdTaO4 and SmTaO4 under compression. For NdTaO4 and SmTaO4, ambient unit [...] Read more.
In this manuscript, we report the density functional theory-based first principles study of the structural and vibrational properties of technologically relevant M′ fergusonite (P2/c)-structured NdTaO4 and SmTaO4 under compression. For NdTaO4 and SmTaO4, ambient unit cell parameters, along with constituent polyhedral volume and bond lengths, have been compared with earlier reported parameters for EuTaO4 and GdTaO4 for a better understanding of the role of lanthanide radii on the primitive unit cell. For both the compounds, our calculations show the presence of first-order monoclinic to tetragonal phase transition accompanied by nearly a 1.3% volume collapse and an increase in oxygen coordination around the tantalum (Ta) cation from ambient six to eight at phase transition. A lower bulk modulus obtained in the high-pressure tetragonal phase when compared to the ambient monoclinic phase is indicative of the more compressible unit cell under pressure. Phonon modes are calculated for the ambient and high-pressure phases with compression for both the compounds along with their pressure coefficients. One particular IR mode has been observed to show red shift in the ambient monoclinic phase, possibly leading to the instability in the compounds under compression. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Volume II))
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11 pages, 9939 KiB  
Article
Strain-Rate Dependence of Plasticity and Phase Transition in [001]-Oriented Single-Crystal Iron
by Nourou Amadou, Abdoul Razak Ayouba Abdoulaye, Thibaut De Rességuier and André Dragon
Crystals 2023, 13(2), 250; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst13020250 - 01 Feb 2023
Cited by 3 | Viewed by 1210
Abstract
Non-equilibrium molecular dynamics simulations have been used to investigate strain-rate dependence of plasticity and phase transition in [001]-oriented single-crystal iron under ramp compression. Here, plasticity is governed by deformation twinning, in which kinetics is tightly correlated with the loading rate. Over the investigated [...] Read more.
Non-equilibrium molecular dynamics simulations have been used to investigate strain-rate dependence of plasticity and phase transition in [001]-oriented single-crystal iron under ramp compression. Here, plasticity is governed by deformation twinning, in which kinetics is tightly correlated with the loading rate. Over the investigated range of strain rates, a hardening-like effect is found to shift the onset of the structural bcc-to-hcp phase transformation to a high, almost constant stress during the ramp compression regime. However, when the ramp evolves into a shock wave, the bcc–hcp transition is triggered whenever the strain rate associated with the plastic deformation reaches some critical value, which depends on the loading rate, leading to a constitutive functional dependence of the transition onset stress on the plastic deformation rate, which is in overall consistence with the experimental data under laser compression. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Volume II))
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12 pages, 4364 KiB  
Article
Phase Transformation Pathway of DyPO4 to 21.5 GPa
by Jai Sharma, Henry Q. Afful and Corinne E. Packard
Crystals 2023, 13(2), 249; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst13020249 - 01 Feb 2023
Cited by 2 | Viewed by 1441
Abstract
Interest in the deformation behavior and phase transformations of rare earth orthophosphates (REPO4s) spans several fields of science—from geological impact analysis to ceramic matrix composite engineering. In this study, the phase behavior of polycrystalline, xenotime DyPO4 is studied up to [...] Read more.
Interest in the deformation behavior and phase transformations of rare earth orthophosphates (REPO4s) spans several fields of science—from geological impact analysis to ceramic matrix composite engineering. In this study, the phase behavior of polycrystalline, xenotime DyPO4 is studied up to 21.5(16) GPa at ambient temperature using in situ diamond anvil cell synchrotron X-ray diffraction. This experiment reveals a large xenotime–monazite phase coexistence pressure range of 7.6(15) GPa and evidence for the onset of a post-monazite transformation at 13.9(10) GPa to scheelite. The identification of scheelite as the post-monazite phase of DyPO4, though not definitive, is consistent with REPO4 phase transformation pathways reported in both the experimental and the computational literature. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Volume II))
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19 pages, 2882 KiB  
Article
Pressure-Induced Structural Phase Transitions in the Chromium Spinel LiInCr4O8 with Breathing Pyrochlore Lattice
by Meera Varma, Markus Krottenmüller, H. K. Poswal and C. A. Kuntscher
Crystals 2023, 13(2), 170; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst13020170 - 18 Jan 2023
Cited by 1 | Viewed by 1443
Abstract
This study reports high-pressure structural and spectroscopic studies on polycrystalline cubic chromium spinel compound LiInCr4O8. According to pressure-dependent X-ray diffraction measurements, three structural phase transitions occur at ∼14 GPa, ∼19 GPa, and ∼36 GPa. The first high-pressure phase is [...] Read more.
This study reports high-pressure structural and spectroscopic studies on polycrystalline cubic chromium spinel compound LiInCr4O8. According to pressure-dependent X-ray diffraction measurements, three structural phase transitions occur at ∼14 GPa, ∼19 GPa, and ∼36 GPa. The first high-pressure phase is indexed to the low-temperature tetragonal phase of the system which coexists with the ambient phase before transforming to the second high-pressure phase at ∼19 GPa. The pressure-dependent Raman and infrared spectroscopic measurements show a blue-shift of the phonon modes and the crystal field excitations and an increase in the bandgap under compression. During pressure release, the sample reverts to its ambient cubic phase, even after undergoing multiple structural transitions at high pressures. The experimental findings are compared to the results of first principles based structural and phonon calculations. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Volume II))
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17 pages, 4952 KiB  
Article
Ab Initio Theoretical Study of DyScO3 at High Pressure
by Enrique Zanardi, Silvana Radescu, Andrés Mujica, Plácida Rodríguez-Hernández and Alfonso Muñoz
Crystals 2023, 13(2), 165; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst13020165 - 17 Jan 2023
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Abstract
DyScO3 is a member of a family of compounds (the rare-earth scandates) with exceptional properties and prospective applications in key technological areas. In this paper, we study theoretically the behavior of DyScO3 perovskite under pressures up to about 65 GPa, including [...] Read more.
DyScO3 is a member of a family of compounds (the rare-earth scandates) with exceptional properties and prospective applications in key technological areas. In this paper, we study theoretically the behavior of DyScO3 perovskite under pressures up to about 65 GPa, including its structural and vibrational properties (with an analysis of the Raman and infrared activity), elastic response, and stability. We have worked within the ab initio framework of the density functional theory, using projector-augmented wave potentials and a generalized gradient approximation form to the exchange-correlation functional, including dispersive corrections. We compare our results with existing theoretical and experimental published data and extend the range of previous studies. We also propose a candidate high-pressure phase for this material. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Volume II))
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19 pages, 5288 KiB  
Article
Structural and Luminescence Properties of Cu(I)X-Quinoxaline under High Pressure (X = Br, I)
by Javier Gonzalez-Platas, Ulises R. Rodriguez-Mendoza, Amagoia Aguirrechu-Comeron, Rita R. Hernandez-Molina, Robin Turnbull, Placida Rodriguez-Hernandez and Alfonso Muñoz
Crystals 2023, 13(1), 100; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst13010100 - 05 Jan 2023
Viewed by 1334
Abstract
A study of high-pressure single-crystal X-ray diffraction and luminescence experiments together with ab initio simulations based on the density functional theory has been performed for two isomorphous copper(I) halide compounds with the empirical formula [C8H6Cu2X2N [...] Read more.
A study of high-pressure single-crystal X-ray diffraction and luminescence experiments together with ab initio simulations based on the density functional theory has been performed for two isomorphous copper(I) halide compounds with the empirical formula [C8H6Cu2X2N2] (X = Br, I) up to 4.62(4) and 7.00(4) GPa for X-ray diffraction and 6.3(4) and 11.6(4) GPa for luminescence, respectively. An exhaustive study of compressibility has been completed by means of determination of the isothermal equations of state and structural changes with pressure at room temperature, giving bulk moduli of K0 = 14.4(5) GPa and K0 = 7.7(6) for the bromide compound and K0 = 13.0(2) GPa and K0 = 7.4(2) for the iodide compound. Both cases exhibited a phase transition of second order around 3.3 GPa that was also detected in luminescence experiments under the same high-pressure conditions, wherein redshifts of the emission bands with increasing pressure were observed due to shortening of the Cu–Cu distances. Additionally, ab initio studies were carried out which confirmed the results obtained experimentally, although unfortunately, the phase transition was not predicted. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Volume II))
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17 pages, 5947 KiB  
Article
First-Principle Study of Ca3Y2Ge3O12 Garnet: Dynamical, Elastic Properties and Stability under Pressure
by Alfonso Muñoz and Plácida Rodríguez-Hernández
Crystals 2023, 13(1), 29; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst13010029 - 24 Dec 2022
Viewed by 1452
Abstract
We present here an ab initio study under the framework of the Density Functional Theory of the Ca3Y2Ge3O12 garnet. Our study focuses on the analysis of the structural, electronic, dynamic, and elastic properties of this material [...] Read more.
We present here an ab initio study under the framework of the Density Functional Theory of the Ca3Y2Ge3O12 garnet. Our study focuses on the analysis of the structural, electronic, dynamic, and elastic properties of this material under hydrostatic pressure. We report information regarding the equation of state, the compressibility, and the structural evolution of this compound. The dynamical properties and the evolution under pressure of infrared, silent, and Raman frequencies and their pressure coefficients are also presented. The dependence on the pressure of the elastic constants and the mechanical and elastic properties are analyzed. From our results, we conclude that this garnet becomes mechanically unstable at 45.7 GPa; moreover, we also find evidence of soft phonons at 34.4 GPa, showing the dynamical instability of this compound above this pressure. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Volume II))
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10 pages, 2532 KiB  
Article
Phase Relations of Ni2In-Type and CaC2-Type Structures Relative to Fe2P-Type Structure of Titania at High Pressure: A Comparative Study
by Khaldoun Tarawneh and Yahya Al-Khatatbeh
Crystals 2023, 13(1), 9; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst13010009 - 21 Dec 2022
Viewed by 1219
Abstract
Density functional theory (DFT) based on first-principles calculations was used to study the high-pressure phase stability of various phases of titanium dioxide (TiO2) at extreme pressures. We explored the phase relations among the following phases: the experimentally identified nine-fold hexagonal Fe [...] Read more.
Density functional theory (DFT) based on first-principles calculations was used to study the high-pressure phase stability of various phases of titanium dioxide (TiO2) at extreme pressures. We explored the phase relations among the following phases: the experimentally identified nine-fold hexagonal Fe2P-type phase, the previously predicted ten-fold tetragonal CaC2-type phase of TiO2, and the recently proposed eleven-fold hexagonal Ni2In-type phase of the similar dioxides zirconia (ZrO2) and hafnia (HfO2). Our calculations, using the generalized gradient approximation (GGA), predicted the Fe2P → Ni2In transition to occur at 564 GPa and Fe2P → CaC2 at 664 GPa. These transitions were deeply investigated with reference to the volume reduction, coordination number decrease, and band gap narrowing to better determine the favorable post-Fe2P phase. Furthermore, it was found that both transitions are mostly driven by the volume reduction across transitions in comparison with the small contribution of the electronic energy gain. Additionally, our computed Birch–Murnaghan equation of state for the three phases reveals that CaC2 is the densest phase, while Ni2In is the most compressible phase. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Volume II))
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13 pages, 1467 KiB  
Article
Stability of FeVO4-II under Pressure: A First-Principles Study
by Pricila Betbirai Romero-Vázquez, Sinhué López-Moreno and Daniel Errandonea
Crystals 2022, 12(12), 1835; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12121835 - 15 Dec 2022
Cited by 4 | Viewed by 2210
Abstract
In this work, we report first-principles calculations to study FeVO4 in the CrVO4-type (phase II) structure under pressure. Total-energy calculations were performed in order to analyze the structural parameters, the electronic, elastic, mechanical, and vibrational properties of FeVO4 [...] Read more.
In this work, we report first-principles calculations to study FeVO4 in the CrVO4-type (phase II) structure under pressure. Total-energy calculations were performed in order to analyze the structural parameters, the electronic, elastic, mechanical, and vibrational properties of FeVO4-II up to 9.6 GPa for the first time. We found a good agreement in the structural parameters with the experimental results available in the literature. The electronic structure analysis was complemented with results obtained from the Laplacian of the charge density at the bond critical points within the Quantum Theory of Atoms in Molecules methodology. Our findings from the elastic, mechanic, and vibrational properties were correlated to determine the elastic and dynamic stability of FeVO4-II under pressure. Calculations suggest that beyond the maximum pressure covered by our study, this phase could undergo a phase transition to a wolframite-type structure, such as in CrVO4 and InVO4. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Volume II))
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13 pages, 1484 KiB  
Article
Corresponding States for Volumes of Elemental Solids at Their Pressures of Polymorphic Transformations
by Oliver Tschauner
Crystals 2022, 12(12), 1698; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12121698 - 23 Nov 2022
Viewed by 1049
Abstract
Many non-molecular elemental solids exhibit common features in their structures over the range of 0 to 0.5 TPa that have been correlated with equivalent valence electron configurations. Here, it is shown that the pressures and volumes at polymorphic transitions obey corresponding states given [...] Read more.
Many non-molecular elemental solids exhibit common features in their structures over the range of 0 to 0.5 TPa that have been correlated with equivalent valence electron configurations. Here, it is shown that the pressures and volumes at polymorphic transitions obey corresponding states given by a single, empirical universal step-function Vtr/L = −0.0208(3) · Ptr + Ni, where Vtr is the atomic volume in Å3 at a given transformation pressure Ptr in GPa, and L is the principal quantum number. Ni assumes discrete values of approximately 20, 30, 40, etc. times the cube of the Bohr radius, thus separating all 113 examined polymorphic elements into five discrete sets. The separation into these sets is not along L. Instead, strongly contractive polymorphic transformations of a given elemental solid involve changes to different sets. The rule of corresponding states allows for predicting atomic volumes of elemental polymorphs of hitherto unknown structures and the transitions from molecular into non-molecular phases such as for hydrogen. Though not an equation of state, this relation establishes a basic principle ruling over a vast range of simple and complex solid structures that confirms that effective single-electron-based calculations are good approximations for these materials and pressures The relation between transformation pressures and volumes paves the way to a quantitative assessment of the state of very dense matter intermediate between the terrestrial pressure regime and stellar matter. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Volume II))
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14 pages, 932 KiB  
Article
Effects of Physical and Chemical Pressure on Charge Density Wave Transitions in LaAg1−xAuxSb2 Single Crystals
by Li Xiang, Dominic H. Ryan, Paul C. Canfield and Sergey L. Bud’ko
Crystals 2022, 12(12), 1693; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12121693 - 23 Nov 2022
Cited by 1 | Viewed by 1121
Abstract
The structural characterization and electrical transport measurements at ambient and applied pressures of the compounds of the LaAg1xAuxSb2 family are presented. Up to two charge density wave (CDW) transitions could be detected upon cooling from room [...] Read more.
The structural characterization and electrical transport measurements at ambient and applied pressures of the compounds of the LaAg1xAuxSb2 family are presented. Up to two charge density wave (CDW) transitions could be detected upon cooling from room temperature and an equivalence of the effects of chemical and physical pressure on the CDW ordering temperatures was observed with the unit cell volume being a salient structural parameter. As such LaAg1xAuxSb2 is a rare example of a non-cubic system that exhibits good agreement between the effects of applied, physical, pressure and changes in unit cell volume from steric changes induced by isovalent substitution. Additionally, for LaAg0.54Au0.46Sb2 anomalies in low temperature electrical transport were observed in the pressure range where the lower charge density wave is completely suppressed. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Volume II))
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11 pages, 3876 KiB  
Article
Understanding the Semiconducting-to-Metallic Transition in the CF2Si Monolayer under Shear Tensile Strain
by Tarik Ouahrani and Reda M. Boufatah
Crystals 2022, 12(10), 1476; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12101476 - 18 Oct 2022
Cited by 1 | Viewed by 1012
Abstract
With the ever-increasing interest in low-dimensional materials, it is urgent to understand the effect of strain on these kinds of structures. In this study, taking the CF2Si monolayer as an example, a computational study was carried out to investigate the effect [...] Read more.
With the ever-increasing interest in low-dimensional materials, it is urgent to understand the effect of strain on these kinds of structures. In this study, taking the CF2Si monolayer as an example, a computational study was carried out to investigate the effect of tensile shear strain on this compound. The structure was dynamically and thermodynamically stable under ambient conditions. By applying tensile shear, the structure showed a strain-driven transition from a semiconducting to a metallic behavior. This electronic transition’s nature was studied by means of the electron localization function index and an analysis of the noncovalent interactions. The result showed that the elongation of covalent bonds was not responsible for this metallization but rather noncovalent interactions governing the nonbonded bonds of the structure. This strain-tuned behavior might be capable of developing new devices with multiple properties involving the change in the nature of chemical bonding in low-dimensional structures. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Volume II))
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12 pages, 2499 KiB  
Article
Chinese Colorless HPHT Synthetic Diamond Inclusion Features and Identification
by Ying Ma, Zhili Qiu, Xiaoqin Deng, Ting Ding, Huihuang Li, Taijin Lu, Zhonghua Song, Wenfang Zhu and Jinlin Wu
Crystals 2022, 12(9), 1266; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12091266 - 06 Sep 2022
Cited by 2 | Viewed by 2592
Abstract
Chinese HPHT diamonds have improved dramatically in recent years. However, this brings a challenge in identifying type IIa colorless diamonds. In this study, eleven HPHT and three natural, colorless, gem-quality IIa diamonds were analyzed using magnified observation, Raman, PL and chemical element analysis. [...] Read more.
Chinese HPHT diamonds have improved dramatically in recent years. However, this brings a challenge in identifying type IIa colorless diamonds. In this study, eleven HPHT and three natural, colorless, gem-quality IIa diamonds were analyzed using magnified observation, Raman, PL and chemical element analysis. The results show that only HPHT samples possessed kite-like inclusions and lichenoid inclusions, as verified by their complex Raman spectra (100–750 cm−1). Through PL mapping, HPHT and natural IIa diamonds were distinguished by their growth environments, which were reflected by PL peaks at 503, 505, 575, 637, 693, 694 and 737 nm. The chemical components of HPHT IIa diamond carbide inclusions are mainly Fe, Co, Ni and Mn, but those of Natural IIa are mainly Fe and Ni. As a result, the chemical components can be used to distinguish a natural colorless IIa diamond from a synthetic diamond. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Volume II))
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16 pages, 1467 KiB  
Article
On the Definition of Phase Diagram
by Kamil Filip Dziubek
Crystals 2022, 12(9), 1186; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12091186 - 23 Aug 2022
Cited by 2 | Viewed by 2404
Abstract
A phase diagram, which is understood as a graphical representation of the physical states of materials under varied temperature and pressure conditions, is one of the basic concepts employed in high-pressure research. Its general definition refers to the equilibrium state and stability limits [...] Read more.
A phase diagram, which is understood as a graphical representation of the physical states of materials under varied temperature and pressure conditions, is one of the basic concepts employed in high-pressure research. Its general definition refers to the equilibrium state and stability limits of particular phases, which set the stage for its terms of use. In the literature, however, a phase diagram often appears as an umbrella category for any pressure–temperature chart that presents not only equilibrium phases, but also metastable states. The current situation is confusing and may lead to severe misunderstandings. This opinion paper reviews the use of the “phase diagram” term in many aspects of scientific research and suggests some further clarifications. Moreover, this article can serve as a starting point for a discussion on the refined definition of the phase diagram, which is required in view of the paradigm shift driven by recent results obtained using emerging experimental techniques. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Volume II))
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10 pages, 2065 KiB  
Article
Computational Investigation of the Stability of Di-p-Tolyl Disulfide “Hidden” and “Conventional” Polymorphs at High Pressures
by Valeriya Yu. Smirnova, Anna A. Iurchenkova and Denis A. Rychkov
Crystals 2022, 12(8), 1157; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12081157 - 17 Aug 2022
Cited by 3 | Viewed by 1517
Abstract
The investigation of molecular crystals at high pressure is a sought-after trend in crystallography, pharmaceutics, solid state chemistry, and materials sciences. The di-p-tolyl disulfide (CH3−C6H4−S−)2 system is a bright example of high-pressure polymorphism. It [...] Read more.
The investigation of molecular crystals at high pressure is a sought-after trend in crystallography, pharmaceutics, solid state chemistry, and materials sciences. The di-p-tolyl disulfide (CH3−C6H4−S−)2 system is a bright example of high-pressure polymorphism. It contains “conventional” solid–solid transition and a “hidden” form which may be obtained only from solution at elevated pressure. In this work, we apply force field and periodic DFT computational techniques to evaluate the thermodynamic stability of three di-p-tolyl disulfide polymorphs as a function of pressure. Theoretical pressures and driving forces for polymorphic transitions are defined, showing that the compressibility of the γ phase is the key point for higher stability at elevated pressures. Transition state energies are also estimated for α → β and α → γ transitions from thermodynamic characteristics of crystal structures, not exceeding 5 kJ/mol. The β → γ transition does not occur experimentally in the 0.0–2.8 GPa pressure range because transition state energy is greater than 18 kJ/mol. Relations between free Gibbs energy (in assumption of enthalpy) of phases α, β, and γ, as a function of pressure, are suggested to supplement and refine experimental data. A brief discussion of the computational techniques used for high-pressure phase transitions is provided. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Volume II))
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12 pages, 3554 KiB  
Article
An Investigation of the Pressure-Induced Structural Phase Transition of Nanocrystalline α-CuMoO4
by Vinod Panchal, Catalin Popescu and Daniel Errandonea
Crystals 2022, 12(3), 365; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12030365 - 09 Mar 2022
Cited by 3 | Viewed by 2289
Abstract
The structural behavior of nanocrystalline α-CuMoO4 was studied at ambient temperature up to 2 GPa using in situ synchrotron X-ray powder diffraction. We found that nanocrystalline α-CuMoO4 undergoes a structural phase transition into γ-CuMoO4 at 0.5 GPa. The structural sequence [...] Read more.
The structural behavior of nanocrystalline α-CuMoO4 was studied at ambient temperature up to 2 GPa using in situ synchrotron X-ray powder diffraction. We found that nanocrystalline α-CuMoO4 undergoes a structural phase transition into γ-CuMoO4 at 0.5 GPa. The structural sequence is analogous to the behavior of its bulk counterpart, but the transition pressure is doubled. A coexistence of both phases was observed till 1.2 GPa. The phase transition gives rise to a change in the copper coordination from square-pyramidal to octahedral coordination. The transition involves a volume reduction of 13% indicating a first-order nature of the phase transition. This transformation was observed to be irreversible in nature. The pressure dependence of the unit-cell parameters was obtained and is discussed, and the compressibility analyzed. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Volume II))
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Review

Jump to: Research

19 pages, 4623 KiB  
Review
Recent Progress in Phase Stability and Elastic Anomalies of Group VB Transition Metals
by Yixian Wang, Hao Wu, Yingying Liu, Hao Wang, Xiangrong Chen and Huayun Geng
Crystals 2022, 12(12), 1762; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12121762 - 05 Dec 2022
Cited by 2 | Viewed by 1874
Abstract
Recently discovered phase transition and elastic anomaly of compression-induced softening and heating-induced hardening (CISHIH) in group VB transition metals at high-pressure and high-temperature (HPHT) conditions are unique and interesting among typical metals. This article reviews recent progress in the understanding of the structural [...] Read more.
Recently discovered phase transition and elastic anomaly of compression-induced softening and heating-induced hardening (CISHIH) in group VB transition metals at high-pressure and high-temperature (HPHT) conditions are unique and interesting among typical metals. This article reviews recent progress in the understanding of the structural and elastic properties of these important metals under HPHT conditions. Previous investigations unveiled the close connection of the remarkable structural stability and elastic anomalies to the Fermi surface nesting (FSN), Jahn–Teller effect, and electronic topological transition (ETT) in vanadium, niobium, and tantalum. We elaborate that two competing scenarios are emerging from these advancements. The first one focuses on phase transition and phase diagram, in which a soft-mode driven structural transformation of BCC→RH1→RH2→BCC under compression and an RH→BCC reverse transition under heating in vanadium were established by experiments and theories. Similar phase transitions in niobium and tantalum were also proposed. The concomitant elastic anomalies were considered to be due to the phase transition. However, we also showed that there exist some experimental and theoretical facts that are incompatible with this scenario. A second scenario is required to accomplish a physically consistent interpretation. In this alternative scenario, the electronic structure and associated elastic anomaly are fundamental, whereas phase transition is just an outcome of the mechanical instability. We note that this second scenario is promising to reconcile all known discrepancies but caution that the phase transition in group VB metals is elusive and is still an open question. A general consensus on the relationship between the possible phase transitions and the mechanical elasticity (especially the resultant CISHIH dual anomaly, which has a much wider impact), is still unreached. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Volume II))
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