Pressure-Induced Structural Transitions in ${\mathrm{M}\mathrm{g}\mathrm{H}}_{2}$

Pressure-Induced Structural Transitions in ${M g H}_{2}$

P. Vajeeston, P. Ravindran, A. Kjekshus, and H. Fjellvåg

Phys. Rev. Lett. 89, 175506 – Published 8 October 2002

Abstract

The stability of ${M g H}_{2}$ has been studied up to 20 GPa using density-functional total-energy calculations. At ambient pressure $α − {M g H}_{2}$ takes a ${T i O}_{2}$ -rutile-type structure. $α − {M g H}_{2}$ is predicted to transform into $γ − {M g H}_{2}$ at 0.39 GPa. The calculated structural data for $α$ - and $γ − {M g H}_{2}$ are in very good agreement with experimental values. At equilibrium the energy difference between these modifications is very small, and as a result both phases coexist in a certain volume and pressure field. Above 3.84 GPa $γ − {M g H}_{2}$ transforms into $β − {M g H}_{2}$ , consistent with experimental findings. Two further transformations have been identified at still higher pressure: (i) $β$ - to $δ − {M g H}_{2}$ at 6.73 GPa and (ii) $δ$ - to $ϵ − {M g H}_{2}$ at 10.26 GPa.