Structural Phase Transition of Rutile-Type MgH2 at High Pressures

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  • Structural Phase Transition of Rutile-Type MgH<sub>2</sub> at High Pressures

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Abstract

The pressure-induced structural phase transition of MgH2 was examined up to 57 GPa at room temperature. α-MgH2 with the rutile-type structure at ambient conditions transformed to γ-MgH2 with the α-PbO2 structure. A complete conversion to the γ-phase, however, did not take place and these two phases coexisted up to 9 GPa. Above 9 GPa, MgH2 transformed to the orthorhombic phase (HP1-phase), and further to another orthorhombic phase (HP2-phase) at around 17 GPa. Space groups of the HP1-phase and the HP2-phase were concluded to be Pbc21 and Pnma (cotunnite-type), respectively. Cotunnite-type MgH2 was stable at pressures up to 57 GPa. Thus the proposed structural sequence of MgH2 under pressure is rutile-type → α-PbO2Pbc21 → cotunnite-type, with an increase in the coordination number of magnesium ions from 6 to 9.

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