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.

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.

Effect of thermally excited lattice vibrations on the thermodynamic stability of tungsten ditellurides WTe2 under high pressure: A first-principles investigation

2021 ◽  
Vol 186 ◽  
pp. 110024
Author(s):  
A. Ektarawong ◽  
P. Tsuppayakorn-aek ◽  
T. Bovornratanaraks ◽  
B. Alling ◽  
N. Kanchanavatee
Keyword(s):  
High Pressure ◽  
Thermodynamic Stability ◽  
First Principles ◽  
Lattice Vibrations

Structural optimization and physical properties of TcB3 and MoB3 at high-pressure: First-principles

2016 ◽  
Vol 30 (20) ◽  
pp. 1650131 ◽  
Author(s):  
Chun Ying ◽  
Xiaowan Bai ◽  
Yungang Du ◽  
Erjun Zhao ◽  
Lin Lin ◽  
...  
Keyword(s):  
High Pressure ◽  
First Principles ◽  
Density Functional ◽  
Dynamic Properties ◽  
Experimental Studies ◽  
Formation Enthalpy ◽  
High Hardness ◽  
Stable Phase ◽  
Ambient Conditions ◽  
Strong Hybridization

The thermodynamic, mechanical and dynamic properties of TcB3 and MoB3 are systematically investigated at high-pressure by first-principles within density functional theory (DFT). The calculated formation enthalpies are negative for TcB3 with considered structures under the pressure range from 0 to 100 GPa. Triboride hP4-TcB3 (i.e., TcB3 in hP4-OsB3 type structure) has the lowest formation enthalpy of −1.44 eV under ambient condition. The largest shear modulus of 240 GPa and smallest Poisson’s ratio of 0.20 for oP16-TcB3 are comparable to those of 267 GPa and 0.15 for ReB2. The calculated elastic constants show that MB3 (M=Tc and Mo) are mechanically stable at ambient conditions, except for mP8-MoB3. The estimated high hardness of 33.4 and 33.1 GPa for oP16-TcB3 and hP4-TcB3, respectively, are reported for the first time. The calculated lattice parameters for MoB3 are in good agreement with the previously theoretical and experimental studies. Below 13 GPa, hP16-MoB3 and hR24-MoB3 are thermodynamically more favorable than MoB3 in other structures. A pressure-induced phase transition is predicted at 13 GPa from hP16-MoB3 and hR24-MoB3 to hP4-MoB3. Above 13 GPa, hP4-MoB3 becomes the thermodynamically most stable phase among MoB3 in considered structures. All compounds with considered structures are metallic, and the electronic structures of MB3 are governed by a strong hybridization between M-4d and B-2p states. The strong and directional covalent bonding between M-4d and B-2p as well as the strong interlayer interactions of boron layers are correlated to the high hardness of 38.0 and 38.4 GPa for hP16-MoB3 and hR24-MoB3, 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 Theoretical predictions for low-temperature phases, softening of phonons and elastic stiffnesses, and electronic properties of sodium peroxide under high pressure

RSC Advances ◽  
2019 ◽  
Vol 9 (53) ◽  
pp. 30964-30975 ◽  
Author(s):  
Pornmongkol Jimlim ◽  
Prutthipong Tsuppayakorn-aek ◽  
Teerachote Pakornchote ◽  
Annop Ektarawong ◽  
Udomsilp Pinsook ◽  
...  
Keyword(s):  
High Pressure ◽  
Low Temperature ◽  
Electronic Properties ◽  
First Principles ◽  
Harmonic Approximation ◽  
High Pressure Phase ◽  
First Principles Calculations ◽  
Sodium Peroxide ◽  
Theoretical Predictions ◽  
Pressure Phase

High-pressure phase stabilities up to 600 K and the related properties of Na2O2 under pressures up to 300 GPa were investigated using first-principles calculations and the quasi-harmonic approximation.

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.

Thermodynamic Stability of Hexagonal and Rhombohedral Bn at Cvd Conditions from Van der Waals Corrected First Principles Calculations

2019 ◽  
Author(s):  
Henrik Pedersen ◽  
Björn Alling ◽  
Hans Högberg ◽  
Annop Ektarawong
Keyword(s):  
Thin Films ◽  
Thermodynamic Stability ◽  
First Principles ◽  
Thermal Equilibrium ◽  
Density Functional ◽  
Van Der Waals ◽  
Chemical Vapor ◽  
First Principles Calculations ◽  
Functional Theory ◽  
The Stability

Thin films of boron nitride (BN), particularly the sp<sup>2</sup>-hybridized polytypes hexagonal BN (h-BN) and rhombohedral BN (r-BN) are interesting for several electronic applications given band gaps in the UV. They are typically deposited close to thermal equilibrium by chemical vapor deposition (CVD) at temperatures and pressures in the regions 1400-1800 K and 1000-10000 Pa, respectively. In this letter, we use van der Waals corrected density functional theory and thermodynamic stability calculations to determine the stability of r-BN and compare it to that of h-BN as well as to cubic BN and wurtzitic BN. We find that r-BN is the stable sp<sup>2</sup>-hybridized phase at CVD conditions, while h-BN is metastable. Thus, our calculations suggest that thin films of h-BN must be deposited far from thermal equilibrium.

Interaction of Oxidizing and Reductive Components in CO2 Streams with Transport Pipeline Steel X70 at High Pressure and Low Temperature

2019 ◽  
Author(s):  
Andreas Kratzig ◽  
Dirk Bettge ◽  
Hoa Le Quynh ◽  
Ralph Bäßler ◽  
Axel Kranzmann
Keyword(s):  
High Pressure ◽  
Low Temperature ◽  
Pipeline Steel

Chemical equilibrium and chemical kinetics

2018 ◽  
Author(s):  
Dennis Sherwood ◽  
Paul Dalby
Keyword(s):  
Free Energy ◽  
Equilibrium Constant ◽  
Gibbs Free Energy ◽  
Chemical Kinetics ◽  
Chemical Equilibrium ◽  
First Principles ◽  
Effect Of Temperature ◽  
Total System ◽  
Free Energies

Building on the previous chapter, this chapter examines gas phase chemical equilibrium, and the equilibrium constant. This chapter takes a rigorous, yet very clear, ‘first principles’ approach, expressing the total Gibbs free energy of a reaction mixture at any time as the sum of the instantaneous Gibbs free energies of each component, as expressed in terms of the extent-of-reaction. The equilibrium reaction mixture is then defined as the point at which the total system Gibbs free energy is a minimum, from which concepts such as the equilibrium constant emerge. The chapter also explores the temperature dependence of equilibrium, this being one example of Le Chatelier’s principle. Finally, the chapter links thermodynamics to chemical kinetics by showing how the equilibrium constant is the ratio of the forward and backward rate constants. We also introduce the Arrhenius equation, closing with a discussion of the overall effect of temperature on chemical equilibrium.

Low-Temperature Hydrogenation of Mg-Ni-Nb2O5 Alloy Processed by High-Pressure Torsion

2021 ◽  
pp. 160309
Author(s):  
M. Osorio-García ◽  
K. Suárez-Alcántara ◽  
Y. Todaka ◽  
A. Tejeda-Ochoa ◽  
M. Herrera Ramírez ◽  
...  
Keyword(s):  
High Pressure ◽  
Low Temperature ◽  
High Pressure Torsion
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