Comparison of the Phase Transitions of High-pressure Phases of Ammonium Fluoride and Ice at Ambient Pressure

ReO3has been studied at pressures up to 52 GPa by X-ray powder diffraction. The previously observed cubicIm3¯ high-pressure phase was shown to transform to a monoclinic MnF3-related phase at about 3 GPa. All patterns recorded above 12 GPa could be indexed on rhombohedral cells. The compressibility was observed to decrease abruptly at 38 GPa. It is therefore proposed that the oxygen ions are hexagonally close packed above this pressure, giving rise to two rhombohedral phases labelled I and II. The zero-pressure bulk moduliBoof the observed phases were determined and the rhombohedral phase II was found to have an extremely large value of 617 (10) GPa. It was found that ReO3transforms back to thePm3¯mphase found at ambient pressure.

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High-pressure polymorphism in l-threonine between ambient pressure and 22 GPa

CrystEngComm ◽

10.1039/c9ce00388f ◽

2019 ◽

Vol 21 (30) ◽

pp. 4444-4456 ◽

Cited By ~ 11

Author(s):

Nico Giordano ◽

Christine M. Beavers ◽

Konstantin V. Kamenev ◽

William G. Marshall ◽

Stephen A. Moggach ◽

...

Keyword(s):

High Pressure ◽

Hydrogen Bonding ◽

Phase Transitions ◽

Amino Acid ◽

Molecular Conformation ◽

Ambient Pressure ◽

Three Phase

The amino acid l-threonine undergoes three phase transitions between ambient pressure and 22.3 GPa which modify both hydrogen bonding and the molecular conformation.

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Brief Review of the Effects of Pressure on Wolframite-Type Oxides

10.20944/preprints201801.0070.v1 ◽

2018 ◽

Author(s):

Daniel Errandonea ◽

Javier Ruiz-Fuertes

Keyword(s):

High Pressure ◽

Phase Transitions ◽

Band Gap ◽

Ambient Pressure ◽

Structural Phase ◽

Band Gap Energy ◽

Structural Phase Transitions ◽

Gap Energy ◽

Raman Modes ◽

Oxygen Bond

In this article we review the advances that have been made on the understanding of the high-pressure structural, vibrational, and electronic properties of wolframite-type oxides since the first works in the early 1990s. Mainly tungstates, which are the best known wolframites, but also tantalates and niobates, with an isomorphic ambient-pressure wolframite structure, have been included in this review. Apart from estimating the bulk moduli of all known wolframites; the cation-oxygen bond distances and their change with pressure have been correlated with their compressibility. The composition variations of all wolframites have been employed to understand their different structural phase transitions to post-wolframite structures as a response to high pressure. The number of Raman modes and band gap energy changes have been also analyzed in the basis of these compositional differences. The reviewed results are relevant for both fundamental science and for the development of wolframites as scintillating detectors. The possible next research venues of wolframites have also been evaluated.

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Structural relationships between cations and alloys; an equivalence between oxidation and pressure

Acta Crystallographica Section B Structural Science ◽

10.1107/s0108768101019310 ◽

2001 ◽

Vol 58 (1) ◽

pp. 38-51 ◽

Cited By ~ 78

Author(s):

Angel Vegas ◽

Martin Jansen

Keyword(s):

High Pressure ◽

Phase Transitions ◽

General Principle ◽

Physical Meaning ◽

Ambient Pressure ◽

Ambient Conditions ◽

Ionic Model ◽

Structural Relationships ◽

Structural Identity ◽

Binary Compounds

More than 100 examples are provided of the structural identity between the cation arrays in oxides and their corresponding alloys (binary compounds). Halides and halogenates, sulfides and sulfites and/or sulfates, selenides and selenates, phosphides and phosphates show this behaviour. In some cases, the structure of the cation subarray corresponds to the structure of the alloy at ambient conditions, but in other cases, cations stabilize structures which correspond to those of the high-pressure phases of the alloy, from which an analogy between the insertion of oxygen and the application of pressure can be established. In this last case, the oxides show polymorphism with temperature and when heated, the structure of the ambient pressure of the alloy is recovered as if heating would compensate the effect of pressure. From the results reported here, it is concluded that cations do not seem to be either the isolated entities, predicted by the ionic model, which occupy interstices of an oxygen matrix, or they arrange in a more or less arbitrary way, but they try to reproduce the structure of their corresponding alloy. Many of the phase transitions and the polymorphism exhibited by the oxides described here are better explained when they are considered as formed by previous entities which are the alloys. Oxides should be considered as `real stuffed alloys'. These features do not seem to be casual, but they obey a general principle: Cations recognize themselves in spite of being embedded in an oxygen bulk. The nature and the physical meaning of this recognition are problems which remain unsolved.

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Phase transitions and enhanced conductivity of CaC2under high pressure

Acta Crystallographica Section A Foundations and Advances ◽

10.1107/s2053273314098404 ◽

2014 ◽

Vol 70 (a1) ◽

pp. C159-C159

Author(s):

Kuo Li ◽

Haiyan Zheng ◽

Chris. Tulk ◽

Ilia Ivanov ◽

Wenge Yang ◽

...

Keyword(s):

Phase Transition ◽

High Pressure ◽

Phase Transitions ◽

Neutron Diffraction ◽

Phase I ◽

Turning Point ◽

Ambient Pressure ◽

Experimental Investigations ◽

Pressure Curve ◽

Structural Transitions

Calcium carbide is widely used in the industry for the production of acetylene and other purposes. Its phase transitions under ambient pressure have been studied since 1930s [1]. In recent years, with the development of high pressure science, its phase transitions under high pressure attracted more attentions [2], and its physical properties such as conductivity and superconductivity were focused [3]. Up to now, most of the researches on CaC2 under high pressure are theoretical, and experimental investigations are expected to figure out the structural transitions. In this work, we investigated the structural transitions of CaC2 (phase I, tetragonal, I4/mmm) up to ~30 GPa by powder XRD, neutron diffraction, and neutron PDF analysis on the recovered samples, and measured the conductivity of CaC2 up to ~20 GPa. XRD data are employed to refine the unit cell parameters, based on which the equation of state is fitted. As identified by series of fittings, the tetragonal phase stabilizes up to 10 GPa, above which it has a minor phase transition. The crystal structures were refined by the structural model of phase I with in-situ neutron diffraction data. Both of the bond length of C-C triple bond and the nearest intergroup C...C distance show a turning point at around 10-12 GPa. The critical pressure is in consistent with the predicted phase transition from phase I to phase VI (monoclinic, I2/m), though the phase VI can't be identified and refined with the data under the current resolution. The resistivity of CaC2 decreases from 1000 Ω·m at 2 GPa to 0.0001 Ω·m at 22 GPa, which can be attributed to the compression of intergroup C...C distance from 0.335nm to 0.315nm. The resistivity-pressure curve also shows a turning point at ~10GPa, corresponding to the phase transition. Above 18 GPa, CaC2 starts to amorphize, which is reversible but sluggish. The C22- may get connected to each other, as observed in the neutron PDF data of the recovered sample.

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Quasiparticle self-consistent GW band structures and high-pressure phase transitions of LiGaO2 and NaGaO2

Physical Review B ◽

10.1103/physrevb.103.045201 ◽

2021 ◽

Vol 103 (4) ◽

Author(s):

Santosh Kumar Radha ◽

Amol Ratnaparkhe ◽

Walter R. L. Lambrecht

Keyword(s):

High Pressure ◽

Phase Transitions ◽

High Pressure Phase ◽

Band Structures ◽

Self Consistent ◽

Pressure Phase

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High-Pressure Spectroscopy Study of Zn(IO3)2 Using Far-Infrared Synchrotron Radiation

Crystals ◽

10.3390/cryst11010034 ◽

2020 ◽

Vol 11 (1) ◽

pp. 34

Author(s):

Akun Liang ◽

Robin Turnbull ◽

Enrico Bandiello ◽

Ibraheem Yousef ◽

Catalin Popescu ◽

...

Keyword(s):

High Pressure ◽

Phase Transitions ◽

Synchrotron Radiation ◽

Infrared Radiation ◽

Room Temperature ◽

Far Infrared ◽

Low Pressure ◽

Pressure Response ◽

Spectroscopy Study ◽

Far Infrared Radiation

We report the first high-pressure spectroscopy study on Zn(IO3)2 using synchrotron far-infrared radiation. Spectroscopy was conducted up to pressures of 17 GPa at room temperature. Twenty-five phonons were identified below 600 cm−1 for the initial monoclinic low-pressure polymorph of Zn(IO3)2. The pressure response of the modes with wavenumbers above 150 cm−1 has been characterized, with modes exhibiting non-linear responses and frequency discontinuities that have been proposed to be related to the existence of phase transitions. Analysis of the high-pressure spectra acquired on compression indicates that Zn(IO3)2 undergoes subtle phase transitions around 3 and 8 GPa, followed by a more drastic transition around 13 GPa.

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Study on the Phase Selection and Debye Temperature of Hyper-Peritectic Al-Ni Alloy under High Pressure

Metals ◽

10.3390/met11010084 ◽

2021 ◽

Vol 11 (1) ◽

pp. 84

Author(s):

Xiaohong Wang ◽

Zhipeng Chen ◽

Duo Dong ◽

Dongdong Zhu ◽

Hongwei Wang ◽

...

Keyword(s):

High Pressure ◽

Ambient Pressure ◽

Competitive Growth ◽

Phase Selection ◽

Debye Temperatures ◽

Ni Alloy ◽

Temperature Heat ◽

Low Temperature Heat Capacity ◽

New Phase ◽

Selection Of

The phase selection of hyper-peritectic Al-47wt.%Ni alloy solidified under different pressures was investigated. The results show that Al3Ni2 and Al3Ni phases coexist at ambient pressure, while another new phase α-Al exists simultaneously when solidified at high pressure. Based on the competitive growth theory of dendrite, a kinetic stabilization of metastable peritectic phases with respect to stable ones is predicted for different solidification pressures. It demonstrates that Al3Ni2 phase nucleates and grows directly from the undercooled liquid. Meanwhile, the Debye temperatures of Al-47wt.%Ni alloy that fabricated at different pressures were also calculated using the low temperature heat capacity curve.

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