Crystal structure, compressibility and possible phase transitions in \boldvarepsilon-FeSi studied by first-principles pseudopotential calculations

1999 ◽  
Vol 55 (4) ◽  
pp. 484-493 ◽  
Author(s):  
Lidunka Vočadlo ◽  
Geoffrey D. Price ◽  
I. G. Wood
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Phase Transitions ◽  
First Principles ◽  
Stable Phase ◽  
Third Order ◽  
First Derivative ◽  
Pseudopotential Calculations ◽  
Cscl Type ◽  
Murnaghan Equation

An investigation of the relative stability of the FeSi structure and of some hypothetical polymorphs of FeSi has been made by first-principles pseudopotential calculations. It has been shown that the observed distortion from ideal sevenfold coordination is essential in stabilizing the FeSi structure relative to one of the CsCl type. Application of high pressure to FeSi is predicted to produce a structure having nearly perfect sevenfold coordination. However, it appears that FeSi having a CsCl-type structure will be the thermodynamically most stable phase for pressures greater than 13 GPa. Fitting of the calculated internal energy vs volume for the FeSi structure to a third-order Birch–Murnaghan equation of state led to values, at T = 0 K, for the bulk modulus, K 0, and for its first derivative with respect to pressure, K 0′, of 227 GPa and 3.9, respectively.

Structures and physical properties of ∊-FeSi-type and CsCl-type RuSi studied by first-principles pseudopotential calculations

2000 ◽  
Vol 56 (3) ◽  
pp. 369-376 ◽  
Author(s):  
Lidunka Vočadlo ◽  
Geoffrey D. Price ◽  
I. G. Wood
Keyword(s):  
High Pressure ◽  
First Principles ◽  
Stable Phase ◽  
Band Structure Calculations ◽  
Pseudopotential Calculations ◽  
Cscl Type ◽  
Logarithmic Equation ◽  
Structure Calculations ◽  
Cell Volumes ◽  
Good Agreement

An investigation of the relative stability of the two known polymorphs of RuSi, having the ∊-FeSi and CsCl structures, has been made by first-principles pseudopotential calculations. The resulting cell volumes and fractional coordinates at P = 0 are in good agreement with experiment. Application of high pressure to the ∊-FeSi phase of RuSi is predicted to produce a structure having almost perfect sevenfold coordination. However, it appears that RuSi having the CsCl-type structure will be the thermodynamically most stable phase for pressures greater than 3.6 GPa. Fitting of the calculated internal energy versus volume to a fourth-order logarithmic equation of state led to values (at T = 0 K) for the bulk modulus, K 0, of 202 and 244 GPa for the ∊-FeSi and CsCl phases, respectively, in excellent agreement with experiment. Band-structure calculations for both phases are also presented.

scholarly journals Unbiased crystal structure prediction of NiSi under high pressure

2015 ◽  
Vol 48 (3) ◽  
pp. 906-908 ◽  
Author(s):  
Pavel N. Gavryushkin ◽  
Zakhar I. Popov ◽  
Konstantin D. Litasov ◽  
Alex Gavryushkin
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Structure Prediction ◽  
Type Structure ◽  
Stable Phase ◽  
Stable Form ◽  
Model Structure ◽  
Crystal Structure Prediction ◽  
Cscl Type ◽  
Pressure Phase

On the basis of an unbiased structure prediction, it is shown that the stable form of NiSi under pressures of 100 and 200 GPa is thePmmnstructure. Furthermore, a new stable phase has been discovered: the deformed tetragonal CsCl-type structure witha= 2.174 Å andc= 2.69 Å at 400 GPa. Specifically, the sequence of high-pressure phase transitions is the following: thePmmnstructure below 213 GPa, the tetragonal CsCl type in the range 213–522 GPa, and cubic CsCl higher than 522 GPa. As the CsCl-type structure is considered as the model structure of the FeSi compound at the conditions of the Earth's core, this result implies restrictions on the Fe–Ni isomorphic miscibility in FeSi.

Elasticity and high-pressure structure of arsenoflorencite-(La): insights into the high-pressure behaviour of the alunite supergroup

2012 ◽  
Vol 76 (4) ◽  
pp. 975-985 ◽  
Author(s):  
S. J. Mills ◽  
F. Nestola
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Phase Transformation ◽  
Volume Data ◽  
Third Order ◽  
X Ray ◽  
Compression Mechanism ◽  
Internal Angle ◽  
Murnaghan Equation ◽  
First Time

AbstractArsenoflorencite-(La), ideally LaAl3(AsO4)2(OH)6, was studied at high pressure by single-crystal X-ray diffractometry. The unit cell was determined at nine pressures up to 7.471(8) GPa; no evidence of a phase transformation was found in this range. The pressure volume data (refined simultaneously) were fitted to a third-order Birch Murnaghan equation of state which gave V0 = 710.71(8) Å3, KT0 = 106(2) GPa and K' = 9.2(9). These values were confirmed independently from an FE–fE plot. The crystal structure was refined at 1.596, 3.622, 5.749 and 7.471 GPa, the first time this has been done for a member the alunite supergroup. The compressibility of arsenoflorencite-(La) is strongly anisotropic, with βc > βa. The main compression mechanism was found to be governed by the internal angle O3 La O2 of the La polyhedron, where the O2 and O3 atoms move toward the c axis during compression.

STRUCTURAL PHASE TRANSITIONS AND MECHANICAL PROPERTIES OF OsO2 UNDER HIGH PRESSURE

2010 ◽  
Vol 24 (22) ◽  
pp. 4269-4279 ◽  
Author(s):  
YONGCHENG LIANG ◽  
ANHU LI ◽  
QIUHONG SONG
Keyword(s):  
Mechanical Properties ◽  
High Pressure ◽  
Phase Transitions ◽  
First Principles ◽  
Structural Phase ◽  
Fluorite Phase ◽  
Structural Phase Transitions ◽  
Pseudopotential Calculations ◽  
Excellent Candidate ◽  
High Bulk

The structural phase transitions, mechanical properties and electronic structures of OsO 2 under high pressure are systemically investigated by the first-principles plane-wave basis pseudopotential calculations. The possible pressure-induced transition sequence in OsO 2 may be the rutile, pyrite and fluorite phases, and the stable CaCl 2 structure is not found. The fluorite phase has high bulk modulus (355.3 GPa), large shear modulus G (267.9 GPa), and huge elastic constant C44 (292.7 GPa), and consequently is an excellent candidate of superhard materials. Crystal structures, valence electron densities, band structures, DOS and PDOS of the rutile, pyrite and fluorite phases of OsO 2 have also been carefully analyzed to elucidate their mechanical properties.

A high-pressure induced stable phase of Li2MnSiO4 as an effective poly-anion cathode material from simulations

2019 ◽  
Vol 7 (27) ◽  
pp. 16406-16413 ◽  
Author(s):  
Shuo Wang ◽  
Junyi Liu ◽  
Yu Qie ◽  
Sheng Gong ◽  
Cunzhi Zhang ◽  
...  
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Cathode Material ◽  
First Principles ◽  
High Performance ◽  
First Principles Calculation ◽  
Stable Phase ◽  
Structure Search

A novel poly-anion Li2MnSiO4 material is predicted at high pressure using global crystal structure search combined with first-principles calculation, which shows great potentials as a high-performance cathode.

First Principles Investigations on the Controversy of Structural Phase Transitions in Thorium Dialuminide under Pressure

2021 ◽  
Author(s):  
Ashok Kumar Verma ◽  
Paritosh Modak
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
High Pressure ◽  
Phase Transitions ◽  
First Principles ◽  
Structural Phase ◽  
First Principles Calculations ◽  
Structural Phase Transitions ◽  
Structural Aspects

We study the high pressure structural aspects of thorium dialuminide, ThAl2, by performing evolutionary crystal structure searches and first principles calculations. We predict a phase transition from the ambient AlB2-type...

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 Crystal Structures of Al2Cu Revisited: Understanding Existing Phases and Exploring Other Potential Phases

Metals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 1037 ◽  
Author(s):  
Sai Wang ◽  
Changzeng Fan
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Single Crystal ◽  
First Principles ◽  
First Principles Calculations ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structural Relationships ◽  
Al2cu Phase ◽  
High Pressure Sintering

When processing single crystal X-ray diffraction datasets for twins of Al2Cu sample synthesized by the high-pressure sintering (HPS) method, we have clarified why the crystal structure of Al2Cu was incorrectly solved about a century ago. The structural relationships between all existing Al2Cu phases, including the Owen-, θ-, θ’-, and Ω-Al2Cu phases, were investigated and established based on a proposed pseudo Al2Cu phase. Two potential phases have been built up by adjusting the packing sequences of A/B layers of Al atoms that were inherent in all existing Al2Cu phases. The mechanical, thermal, and dynamical stability of two such novel phases and their electronic properties were investigated by first-principles calculations.

The thermodynamic stability of three near-degenerate phases of platinum dioxide

2004 ◽  
Vol 848 ◽  
Author(s):  
Shuping Zhuo ◽  
Karl Sohlberg
Keyword(s):  
High Pressure ◽  
Fixed Point ◽  
Low Temperature ◽  
Thermodynamic Stability ◽  
First Principles ◽  
Energy Surface ◽  
Stable Phase ◽  
Free Energies ◽  
Rutile Structure ◽  
Unstable Fixed Point

ABSTRACTThe thermodynamic stability of the three nearly energy degenerate crystal structures of PtO2 is studied here with first-principles-based calculations of their free energies. For P = 0 the α-(CdI2) structure is the thermodynamically stable phase at low temperature, while the β-(CaCl2) structure is stable at high pressure. The β'-(rutile) structure represents an unstable fixed point on the potential energy surface, or is possibly just barely bound. These results reconcile seemingly contradictory findings and answer longstanding questions about PtO2.

Sign in / Sign up

Export Citation Format

Share Document