New high-pressure phase of MgH2: An ab initio constant-pressure study
Department of Physics, Texas Tech University - Lubbock, TX, 79409, USA and Department of Advanced Materials and Nanotechnology, Abdullah Gül University - Kayseri, 38039, Turkey
Received: 29 November 2013
Accepted: 5 February 2014
The stability of magnesium hydride (MgH2) at high pressure is studied using a constant-pressure ab initio technique. Two phase transformations are successfully observed through the simulations. The rutile structure undergoes a phase transformation into a CaCl2-type phase. Further increase in pressure results into a first-order phase transition into an orthorhombic state within Pbcm symmetry. This phase can be considered as a distorted CaF2-type crystal and does not correspond to the previously proposed MgH2 phases. The transformation mechanism of the CaCl2-Pbcm phase change at the atomistic level is successfully characterized and it is found that the CaCl2-to-Pbcm phase change proceeds via an ideal CaF2-type intermediate phase. These phase transformations are also analyzed using total energy-volume calculations.
PACS: 64.70.K- – Solid-solid transitions / 61.50.Ks – Crystallographic aspects of phase transformations; pressure effects
© EPLA, 2014