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

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.

1976 ◽  
Vol 31 (2) ◽  
pp. 158-162 ◽  
Author(s):  
J. B. Clark ◽  
Klaus-Jügen Range

The structure of the high pressure compounds ZnAs and CdAs have been determined using Guinier film and counter methods. The compounds are orthorhombic, (space group Pbca; Z = 8), with α = 5.679(2) Å, b = 7.277(4) Å, c = 7.559(4) Å and α = 5.993(4) Å, b = 7.819(6) Å, c = 8.011(6) Å respectively.ZnAs and CdAs are isostructural with the normal pressure phases ZnSb and CdSb, which are related to the high pressure phase Si III. Structural relationships are discussed including the Si III-diamond structure relationship.


2017 ◽  
Vol 96 (3) ◽  
Author(s):  
Andriy Smolyanyuk ◽  
Lilia Boeri ◽  
Cesare Franchini

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

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.


1986 ◽  
Vol 33 (6) ◽  
pp. 4221-4226 ◽  
Author(s):  
Samuel T. Weir ◽  
Yogesh K. Vohra ◽  
Arthur L. Ruoff

ACS Omega ◽  
2018 ◽  
Vol 3 (12) ◽  
pp. 18227-18233 ◽  
Author(s):  
Junbo Gong ◽  
Xiaodong Fan ◽  
Rucheng Dai ◽  
Zhongping Wang ◽  
Zejun Ding ◽  
...  

2005 ◽  
Vol 60 (8) ◽  
pp. 815-820 ◽  
Author(s):  
Holger Emme ◽  
Matthias Weil ◽  
Hubert Huppertz

The new orthorhombic polymorph β-HgB4O7 has been synthesized under high-pressure and hightemperature conditions in a Walker-type multianvil apparatus at 7.5 GPa and 600 °C. β-HgB4O7 is isotypic to the known ambient pressure phases MB4O7 (M = Sr, Pb, Eu) and the high-pressure phase β-CaB4O7 crystallizing with two formula units in the space group Pmn21 with lattice parameters a = 1065.6(2), b = 438.10(9), and c = 418.72(8) pm. The relation of the crystal structure of the high-pressure phase β-HgB4O7 to the normal pressure phase α-HgB4O7 as well as the relation to the isotypic phases MB4O7 (M = Sr, Pb, Eu) and β-CaB4O7 are discussed.


2018 ◽  
Vol 122 (2) ◽  
pp. 1267-1279 ◽  
Author(s):  
Claudio Cazorla ◽  
Arun K. Sagotra ◽  
Meredith King ◽  
Daniel Errandonea

2018 ◽  
Vol 98 (9) ◽  
Author(s):  
M. Abdel-Hafiez ◽  
M. Mito ◽  
K. Shibayama ◽  
S. Takagi ◽  
M. Ishizuka ◽  
...  

Sign in / Sign up

Export Citation Format

Share Document