High-pressure formation and stabilization of iridium hydrides

A class of iridium hydrides, IrH_x (x=0.5, 1-4, 6), is calculated at ab-initio level using the DFT. A number of hydrides are predicted to stabilize in the excess hydrogen environment and upon compression. The threshold pressure for thermodynamical stabilization is calculated to ~5 and ~14 GPa at which, respectively, a trihydride (P6_3mc) and a dihydride (Ibam) stabilize with respect to decomposition into pure element. The dihydride (Ibam) is calculated to stabilize dynamically at P~14 GPa and the trihydride at P > 25 GPa. In both the di- and trihydride iridium atoms form short directional contacts with hydrogens, typical for covalent bonds. The trihydride exhibit molecular character and its relative stability is calculated to be higher than that of the dihydride, at least up to approx. 75 GPa.