Theoretical Study of High Pressure Metallic Hydrogen

1990 ◽  
Vol 193 ◽  
Author(s):  
Troy W. Barbee ◽  
Alberto García ◽  
Marvin L. Cohen
Keyword(s):  
High Pressure ◽  
Phase Transitions ◽  
Transition Temperature ◽  
First Principles ◽  
Theoretical Study ◽  
Hexagonal Phase ◽  
Temperature Phase ◽  
Superconducting Transition ◽  
Zero Temperature ◽  
Metallic Hydrogen

ABSTRACTA study of the zero temperature phase transitions in hydrogen under megabar pressures using a first-principles total-energy method is presented. An anisotropic primitive hexagonal phase is found to be particularly stable relative to other monatomic phases for pressures between 4 and 8 megabars. Calculations of the vibrational frequencies show that this phase is unstable with respect to a distortion tripling the unit cell along the c-axis. Results for this distorted hexagonal phase will be presented, including a calculation of its superconducting transition temperature Tc.

Phase Transition and ThermodynamicProperties of OsN2 under High Pressure

2013 ◽  
Vol 401-403 ◽  
pp. 660-662
Author(s):  
Zhi Jian Fu ◽  
Li Jun Jia ◽  
Wei Long Quan
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Thermal Expansion ◽  
Phase Transitions ◽  
Transition Temperature ◽  
Thermodynamic Properties ◽  
First Principles ◽  
Fluorite Structure ◽  
First Principles Calculations ◽  
Zero Temperature

The lattice parameters, phase transition, and thermodynamic properties of OsN2in pyrite and fluorite structure are investigated by first-principles calculations. The pressure and temperature induced phase transitions of OsN2from fluorite structure to pyrite structure have been obtained. It is found that the transition pressure of OsN2at zero temperature is 158.2 GPa, and there exists no transition temperature. In addition, the thermal expansion, the Debye temperature, and the Grüneisen parameter in diverse pressures and temperatures about these two structures have also been obtained. Key words: transition phase; thermodynamic properties; OsN2PACS numbers: 71.15.Mb, 64.70.Kb

Theoretical Study of a new Transition Sequence in III-V Compounds: High-Pressure Phases of InSb

1990 ◽  
Vol 193 ◽  
Author(s):  
Alberto García ◽  
Marvin L. Cohen ◽  
S. B. Zhang
Keyword(s):  
High Pressure ◽  
Total Energy ◽  
First Principles ◽  
Theoretical Study ◽  
Hexagonal Phase ◽  
Structural Models ◽  
Zero Temperature ◽  
Transition Sequence ◽  
Transition Paths ◽  
Bcc Phase

ABSTRACTA detailed study of the pressure-induced phase transitions at zero temperature in InSb up to 40 GPa using a first-principles pseudopotential total-energy method is presented. In addition to InSb(I) (cubic) and (II) (polar β-Sn), we identify InSb(III) as a hexagonal phase (found earlier for GaSb) and (VI) as a polar bcc phase in agreement with recent experiments. New structural models, orthorhombic polar β-Sn and body-centered orthorhombic, are proposed as candidates for the InSb(IV) and (V) phases based on total-energy minimizations. These findings are compared with recent results for GaAs to illustrate the trends in transition paths among III-V compounds.

High Pressure Synthesized Magnesium Diboride- and Dodecaboride-Based Superconductors: Structure and Properties

2010 ◽  
Vol 670 ◽  
pp. 21-27 ◽  
Author(s):  
Tatiana Prikhna ◽  
Wolfgang Gawalek ◽  
Yaroslav Savchuk ◽  
Athanasios G. Mamalis ◽  
Vasiliy Tkach ◽  
...  
Keyword(s):  
High Pressure ◽  
Transition Temperature ◽  
Critical Current Density ◽  
Current Density ◽  
Magnesium Diboride ◽  
Synthesis Temperature ◽  
Superconducting Transition ◽  
Structure And Properties ◽  
Synthesized Materials ◽  
Critical Current Density Jc

The critical current density, jc, of high-pressure synthesized MgB2-based balk materials correlates with the amount and distribution of higher borides (MgB12) and Mg-B-O inclusions, which in tern correlates with the synthesis temperature and presence of additions (Ti, Ta, SiC). High-pressure-synthesized materials with near MgB12 composition of matrix exhibited superconducting transition temperature, Tc, of about 37 K, rather high jc (5∙105 and 103 A/cm2 in 0 T and 3.5 T, respectively, at 20 K) and doubled matrix microhardness: 25±1.1 GPa at 4.9 N –load as compared to materials with MgB2).

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.

scholarly journals First-Principles Calculations of High-Pressure Physical Properties of Ti0.5Ta0.5 Alloy

Symmetry ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 796
Author(s):  
Fang Yu ◽  
Yu Liu
Keyword(s):  
High Pressure ◽  
Physical Properties ◽  
First Principles ◽  
Theoretical Study ◽  
Applied Pressure ◽  
Lattice Parameter ◽  
Physical Parameters ◽  
First Principles Calculations ◽  
Analysis Method ◽  
Metallic Bond

In this paper, an in-depth theoretical study on some physical properties of Ti0.5Ta0.5 alloy with systematic symmetry under high pressure is conducted via first-principles calculations, and relevant physical parameters are calculated. The results demonstrate that the calculated parameters, including lattice parameter, elastic constants, and elastic moduli, fit well with available theoretical and experimental data when the Ti0.5Ta0.5 alloy is under T = 0 and P = 0 , indicating that the theoretical analysis method can effectively predict the physical properties of the Ti0.5Ta0.5 alloy. The microstructure and macroscopic physical properties of the alloy cannot be destroyed as the applied pressure ranges from 0 to 50GPa, but the phase transition of crystal structure may occur in the Ti0.5Ta0.5 alloy if the applied pressure continues to increase according to the TDOS curves and charge density diagram. The value of Young’s and shear modulus is maximized at P = 25   GPa . The anisotropy factors A ( 100 ) [ 001 ] and A ( 110 ) [ 001 ] are equal to 1, suggesting the Ti0.5Ta0.5 alloy is an isotropic material at 28 GPa, and the metallic bond is strengthened under high pressure. The present results provide helpful insights into the physical properties of Ti0.5Ta0.5 alloy.

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