Anin situstructural study of the high-pressure transformations in TiH_0.74

Abstract

Structural phase transitions in the TiH0.74 alloy have been studied in the pressure range extending to 30.5 GPa at temperatures of up to 630 K, using diamond anvils and energy dispersive x-ray diffraction. Two phase transitions were observed at high pressures. At room temperature, the TiH0.74 alloy undergoes a transition to the (η+ω) two-phase state at above 7 GPa, and then this state persists up to 30.5 GPa. The other phase transition occurs upon heating (η+ω)-TiH0.74 to T>560 K to give a single-phase state, ζ-TiH0.74. The ω-phase corresponds to the high-pressure phase of pure titanium. The Ti sublattices of the η- and ζ-phases are indexed within the tetragonal symmetry, their specific volumes being much the same. Analysis of the specific volumes and the hydrogen contents in these two phases suggests that hydrogen atoms are likely to occupy tetrahedral interstices in the ζ-phase and octahedral interstices in the η-phase.