A synchrotron study of high-pressure transformations in TiH0.74

The crystal structure of the TiH0.74 alloy was studied by the energy disper sive X-ray diffraction technique in the pressure range to 30.5 GPa at tempe ratures to 630 K. A phase transformation to the (eta + omega) two-phase sta te was found to occur above 7 GPa at room temperature, then (eta + omega)-T iH0.74 remained stable up to P = 30.5 GPa. Another phase transformation res ulting in a single-phase state, zeta-TiH0.74, was found to occur upon heati ng (eta + omega)-TiH0.74 above T approximate to 560 K. Both high-pressure p hases, eta and zeta, were indexed on the basis of the tetragonal sublattice s of the Ti atoms with nearly the same specific volumes. It is assumed from the relation of the specific volumes that the hydrogen atoms occupy the te trahedral interstices in the zeta-phase and the octahedral interstices in t he eta-phase.