Structural Studies of Group IV Binary Hydrides at Extreme Pressures*

Although binary hydrides such as TiH$_{2}$ are not ideal candidates for storing hydrogen, they can act as active species to catalyze the reversible dehydrogenation of other hydrides and of carbon nanotubes. The equation of state of TiH$_{2}$, ZrH$_{2}$ and HfH$_{2}$ was obtained using synchrotron x-ray diffraction and diamond anvil cells, with structural studies carried out \textit{in situ} on compression up to $\sim $50 GPa, under quasi-hydrostatic conditions. We discuss pressure-induced structural transformations and the experimental bulk modulus for TiH$_{2}$, ZrH$_{2}$ and HfH$_{2}$, accompanied by corresponding first principle calculations.