Effect of high pressure on polymorphic phase transition and electronic structure of XAs (X=Al, Ga, In)

Abstract Metal polyhydrides have attracted considerable attention because some of them become a metal under high pressure, and some undergo a phase transition into a superconductor. Some superconducting metal polyhydrides have recently been discovered with a high value of critical temperature (Tc) under pressure. In this research, we calculated the structures of MgH2, MgH3 and MgD3 under pressure between 0-300 GPa in order to determine the formation enthalpy and electronic property of their structures under high pressure by using density functional theory (DFT) based on the Quantum Espresso code. We found that the band structures reveal the metallic character of the compounds under high pressure. The energy band structures of MgHx and MgDx are exactly the same. However, their phonon dispersions are different due to the so-called isotope effect. We determined the composition stability by using the convex hull of Mg, H and the compounds. We found that MgH3 becomes thermodynamically more stable than MgH2 at around 150 GPa. The results of phonons confirm that they are dynamically stable. This finding is served as a basis for future superconducting calculations.

Download Full-text

First-principles prediction of the high-pressure phase transition and electronic structure of FeO: Implications for the chemistry of the lower mantle and core

Geophysical Research Letters ◽

10.1029/94gl03010 ◽

1995 ◽

Vol 22 (8) ◽

pp. 1001-1004 ◽

Cited By ~ 30

Author(s):

David M. Sherman ◽

Henri J. F. Jansen

Keyword(s):

Phase Transition ◽

High Pressure ◽

Electronic Structure ◽

First Principles ◽

Lower Mantle ◽

High Pressure Phase ◽

High Pressure Phase Transition ◽

Pressure Phase

Download Full-text

Can We Predict the Pressure Induced Phase Transition of Urea? Application of Quantum Molecular Dynamics

Molecules ◽

10.3390/molecules25071584 ◽

2020 ◽

Vol 25 (7) ◽

pp. 1584 ◽

Cited By ~ 1

Author(s):

Anna Mazurek ◽

Łukasz Szeleszczuk ◽

Dariusz Maciej Pisklak

Keyword(s):

Phase Transition ◽

High Pressure ◽

Density Functional ◽

Geometry Optimization ◽

Stable Form ◽

Quantum Molecular Dynamics ◽

Polymorphic Phase Transition ◽

Cell Dimensions ◽

Crystalline Urea ◽

Unit Cell Dimensions

Crystalline urea undergoes polymorphic phase transition induced by high pressure. Form I, which is the most stable form at normal conditions and Form IV, which is the most stable form at 3.10 GPa, not only crystallize in various crystal systems but also differ significantly in the unit cell dimensions. The aim of this study was to determine if it is possible to predict polymorphic phase transitions by optimizing Form I at high pressure and Form IV at low pressure. To achieve this aim, a large number of periodic density functional theory (DFT) calculations were performed using CASTEP. After geometry optimization of Form IV at 0 GPa Form I was obtained, performing energy minimization of Form I at high pressure did not result in Form IV. However, employing quantum molecular isothermal–isobaric (NPT) dynamics calculations enabled to accurately predict this high-pressure transformation. This study shows the potential of different approaches in predicting the polymorphic phase transition and points to the key factors that are necessary to achieve the success.

Download Full-text