PHASE TRANSITION AND THERMODYNAMIC PROPERTIES OF MAGNESIUM FLUORIDE BY FIRST PRINCIPLES

Abstract

The structural stabilities, phase transitions and thermodynamic properties of MgF 2 under high pressure and temperature are investigated by first-principles calculations based on plane-wave pseudopotential density functional theory method within the local density approximation. The calculated lattice parameters of MgF 2 in all four phases under zero pressure and zero temperature are in good agreement with the existing experimental data and other theoretical results. Our results demonstrate that MgF 2 undergoes a series of structural phase transitions from rutile (P42/mnm)→ CaCl 2-type (Pnnm)→ modified fluorite (Pa-3)→ cotunnite (Pnam) under high pressure and the obtained transition pressures are in fairly good agreement with the experimental results. The temperature-dependent volume and thermodynamic properties of MgF 2 in the rutile phase at 0 GPa are presented and the thermodynamic properties of MgF 2 in the rutile, CaCl 2-type, modified fluorite and cotunnite phases at 300 K are also predicted using the quasi-harmonic approximation model (QHA) and the quasi-harmonic Debye model (QHD), respectively. Moreover, the partial density of states and the electronic density of the four phases under the phase transition are also investigated.