Computational investigation of pressure and temperature effects on the structural stability of Mg-H system using the quasi-harmonic model calculations

摘要

We investigate by First Principles Density Functional Theory the hydride phase stability, the crystal structure and the thermodynamics of the polymorphs of MgHa as the first step in understanding the hydride formation in hydrogen storage materials. We focus on the magnesium hydride phases as regularly MgH2 serves as main intermediate to metal-hydride storage materials obtained by doping with transition metal elements such as Ti, V, Mn, Fe, Co, Ni, Cu, Pd, added to improve dehydrogenation and hydrogenation without significantly reducing the hydrogen storage capacity. We have performed a computational investigation of both pressure and temperature effects on the structural changes in the Mg-H system - (rutile Ti02 SG P42/mnm) [1], (cubic modified CaF2, SG Pa3)[2], (orthorhombic PbO2 SG Pbcn)[3] and δ ( orthorhombic SG Pbcd)[4] using the quasi-harmonic model (see the structures in Fig. 1)[5,6].