scholarly journals Compressibility and Phase Stability of Iron-Rich Ankerite

Minerals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 607
Author(s):  
Raquel Chuliá-Jordán ◽  
David Santamaria-Perez ◽  
Javier Ruiz-Fuertes ◽  
Alberto Otero-de-la-Roza ◽  
Catalin Popescu
Keyword(s):  
High Pressure ◽  
Density Functional ◽  
Computational Study ◽  
Density Functional Theory Calculations ◽  
High Pressure Phase ◽  
Stable Phase ◽  
Pressure Derivative ◽  
Reversible Phase Transition ◽  
Murnaghan Equation ◽  
Pressure Phase

The structure of the naturally occurring, iron-rich mineral Ca1.08(6)Mg0.24(2)Fe0.64(4)Mn0.04(1)(CO3)2 ankerite was studied in a joint experimental and computational study. Synchrotron X-ray powder diffraction measurements up to 20 GPa were complemented by density functional theory calculations. The rhombohedral ankerite structure is stable under compression up to 12 GPa. A third-order Birch–Murnaghan equation of state yields V0 = 328.2(3) Å3, bulk modulus B0 = 89(4) GPa, and its first-pressure derivative B’0 = 5.3(8)—values which are in good agreement with those obtained in our calculations for an ideal CaFe(CO3)2 ankerite composition. At 12 GPa, the iron-rich ankerite structure undergoes a reversible phase transition that could be a consequence of increasingly non-hydrostatic conditions above 10 GPa. The high-pressure phase could not be characterized. DFT calculations were used to explore the relative stability of several potential high-pressure phases (dolomite-II-, dolomite-III- and dolomite-V-type structures), and suggest that the dolomite-V phase is the thermodynamically stable phase above 5 GPa. A novel high-pressure polymorph more stable than the dolomite-III-type phase for ideal CaFe(CO3)2 ankerite was also proposed. This high-pressure phase consists of Fe and Ca atoms in sevenfold and ninefold coordination, respectively, while carbonate groups remain in a trigonal planar configuration. This phase could be a candidate structure for dense carbonates in other compositional systems.

scholarly journals A Short Review of Current Computational Concepts for High-Pressure Phase Transition Studies in Molecular Crystals

Crystals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 81 ◽  
Author(s):  
Denis A. Rychkov
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Organic Compounds ◽  
Computational Study ◽  
Molecular Crystals ◽  
High Pressure Phase ◽  
Advantages And Disadvantages ◽  
High Pressure Phase Transition ◽  
Pressure Phase ◽  
Transition Studies

High-pressure chemistry of organic compounds is a hot topic of modern chemistry. In this work, basic computational concepts for high-pressure phase transition studies in molecular crystals are described, showing their advantages and disadvantages. The interconnection of experimental and computational methods is highlighted, showing the importance of energy calculations in this field. Based on our deep understanding of methods’ limitations, we suggested the most convenient scheme for the computational study of high-pressure crystal structure changes. Finally, challenges and possible ways for progress in high-pressure phase transitions research of organic compounds are briefly discussed.

scholarly journals Persistence of the stereochemical activity of the Bi3+ lone electron pair in Bi2Ga4O9 up to 50 GPa and crystal structure of the high-pressure phase

2010 ◽  
Vol 66 (3) ◽  
pp. 323-337 ◽  
Author(s):  
Alexandra Friedrich ◽  
Erick A. Juarez-Arellano ◽  
Eiken Haussühl ◽  
Reinhard Boehler ◽  
Björn Winkler ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
High Pressure ◽  
Density Functional ◽  
Lone Electron Pair ◽  
Electron Pair ◽  
High Pressure Phase ◽  
Functional Theory ◽  
Pressure Phase ◽  
Stereochemical Activity

The crystal structure of the high-pressure phase of bismuth gallium oxide, Bi2Ga4O9, was determined up to 30.5 (5) GPa from in situ single-crystal in-house and synchrotron X-ray diffraction. Structures were refined at ambient conditions and at pressures of 3.3 (2), 6.2 (3), 8.9 (1) and 14.9 (3) GPa for the low-pressure phase, and at 21.4 (5) and 30.5 (5) GPa for the high-pressure phase. The mode-Grüneisen parameters for the Raman modes of the low-pressure structure and the changes of the modes induced by the phase transition were obtained from Raman spectroscopic measurements. Complementary quantum-mechanical calculations based on density-functional theory were performed between 0 and 50 GPa. The phase transition is driven by a large spontaneous displacement of one O atom from a fully constrained position. The density-functional theory (DFT) model confirmed the persistence of the stereochemical activity of the lone electron pair up to at least 50 GPa in accordance with the crystal structure of the high-pressure phase. While the stereochemcial activity of the lone electron pair of Bi^{3+} is reduced at increasing pressure, a symmetrization of the bismuth coordination was not observed in this pressure range. This shows an unexpected stability of the localization of the lone electron pair and of its stereochemical activity at high pressure.

Pressure Driven Structural Phase Transition in EuTaO4: Experimental and First Principles Investigations

2022 ◽  
Author(s):  
Saheli Banerjee ◽  
Alka B Garg ◽  
H. K. Poswal
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
First Principles ◽  
Density Functional ◽  
Structural Phase ◽  
Polycrystalline Sample ◽  
High Pressure Phase ◽  
Spectroscopic Techniques ◽  
Volume Data ◽  
Pressure Phase

Abstract In this article we report the synthesis, characterization and high pressure investigation on technologically important, rare earth orthotantalate, EuTaO4. Single phase polycrystalline sample of EuTaO4 has been synthesized by solid state reaction method adopting monoclinic M'-type fergusonite phase with space group P2/c. Structural and vibrational properties of synthesized compound are investigated using synchrotron based x-ray powder diffraction, and Raman spectroscopic techniques respectively. Both the techniques show presence of an isostructural, first order, reversible phase transition near 17 GPa. Bulk modulus obtained by fitting the experimental pressure volume data for low pressure and high pressure phase is 136.0(3) and 162.8(21) GPa. High pressure phase is accompanied by an increase in coordination number around Ta atom from 6 to 8. First principles calculations under the frame work of density functional theory (DFT) also predicts the isostructural phase transition and change in coordination around Ta atom, corroborating the experimental findings.

Ab Initio Calculation of the System Cr–GaSb: A New High-Pressure Phase Containing Defects

2012 ◽  
Vol 190 ◽  
pp. 35-38
Author(s):  
M.V. Magnitskaya ◽  
E.T. Kulatov ◽  
A.A. Titov ◽  
Y.A. Uspenskii ◽  
E.G. Maksimov ◽  
...  
Keyword(s):  
High Pressure ◽  
Optical Properties ◽  
Ab Initio ◽  
Related Compound ◽  
Density Functional Calculations ◽  
Density Functional ◽  
High Pressure Phase ◽  
X Ray ◽  
Pressure Phase

We report on ab initio density-functional calculations of a novel spintronics-related compound CrGa2Sb2 recently synthesized under high pressure. The effect of Cr deficiency on the electronic, magnetic and optical properties of CrGa2Sb2 is considered. New X-ray structural measurements up to high pressure of 9 GPa are presented.

A new high pressure phase of sodium formate dihydrate; an experimental and computational study

2007 ◽  
pp. 2014 ◽  
Author(s):  
Martin Walker ◽  
Carole A. Morrison ◽  
David R. Allan ◽  
Colin R. Pulham ◽  
William G. Marshall
Keyword(s):  
High Pressure ◽  
Computational Study ◽  
Sodium Formate ◽  
High Pressure Phase ◽  
Pressure Phase

High-pressure phase transitions and equations of state in NiSi. III. A new high-pressure phase of NiSi

2013 ◽  
Vol 46 (1) ◽  
pp. 14-24 ◽  
Author(s):  
Ian G. Wood ◽  
Jabraan Ahmed ◽  
David P. Dobson ◽  
Lidunka Vočadlo
Keyword(s):  
Phase Diagram ◽  
High Pressure ◽  
Ab Initio ◽  
Equations Of State ◽  
Orthorhombic Phase ◽  
High Pressure Phase ◽  
Stable Phase ◽  
Orthorhombic Space Group ◽  
Space Group ◽  
Pressure Phase

A new high-pressure phase of NiSi has been synthesized in a multi-anvil press by quenching samples to room temperature from 1223–1310 K at 17.5 GPa and then recovering them to atmospheric pressure. The crystal structure of this recovered material has been determined from X-ray powder diffraction data; the resulting fractional coordinates are in good agreement with those obtained from anab initiocomputer simulation. The structure, in which each atom is six-fold coordinated by atoms of the other kind, is orthorhombic (space groupPmmn) witha= 3.27,b= 3.03,c= 4.70 Å. This orthorhombic phase of NiSi may be considered as a ferroelastic distortion of the hypothetical tetragonal (space groupP4/nmm) NiSi structure that was predicted to be the most stable phase (at 0 K) for pressures between 23 and 61 GPa in an earlierab initiostudy by Vočadlo, Wood & Dobson [J. Appl. Cryst.(2012),45, 186–196]. Furtherab initiosimulations have now shown that, with increasing pressure (at 0 K), NiSi is predicted to exist in the following polymorphs: (i) the MnP structure; (ii) the new orthorhombic structure with space groupPmmn; and (iii) the CsCl structure. Experimentally, all of these structures have now been observed and, in addition, a fourth polymorph, an ∊-FeSi-structured phase of NiSi (never the most thermodynamically stable phase in athermalab initiosimulations), may be readily synthesized at high pressure (P) and temperature (T). On the basis of both experiments and computer simulations it is therefore now clear that the phase diagram of NiSi at highPandTis complex. The simulated free-energy differences between different structures are often very small (<10 meV atom−1) and there is also the possibility of two displacive ferroelastic phase transformations, the first between structures withPmmnandP4/nmmsymmetry, and the second fromP4/nmmto a different orthorhombic phase of NiSi with space groupPbma. A complete understanding of the NiSi phase diagram (which may be of relevance to both planetary cores and the use of thin films of NiSi in semiconductor technology) can, therefore, only comevia in situexperiments at simultaneous highPand highT.

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