| The structure and behavior of titanium hydride was studied on compression to about a megabar. Angle-dispersive as well as energy-dispersive synchrotron X-ray diffraction studies were carried out in situ, in diamond anvil cells, in several compression and decompression sequences. A phase transition from a cubic to a tetragonal structure was observed. The pressure evolution of the diffraction patterns revealed that the cubic (Fm-3m) to tetragonal ((4/mmm) phase transition occurs at about 0.6 GPa. The transition was found to be reversible on decompression from 34 GPa but irreversible on decompression from 90 GPa. The influence of the pressure transmitting medium on the pressure-induced structural transformations of TiH2 was also examined. An equation of state fit of the evolution of unit cell volume as a function of pressure, up to 90 GPa yielded a zero pressure bulk modulus K0=143(7) GPa, and its pressure derivative K0=3.0(0.1) for the high-pressure tetragonal phase of TiH2. |
