High pressure studies of the erbium-hydrogen system

High-pressure X-ray diffraction investigations up to 25 GPa using diamond anvil cell techniques (DAC) have been carried out on erbium and a series of erbium hydrides. The equations of state have been evaluated for ErH_1.95, ErH_2.091 (in the β-phase) and for γ-ErH₃. For comparison, the compressibility of pure erbium metal has also been determined in the same pressure range. A rapid drop of lattice volume at a pressure of about 14.5 GPa has been observed for ErH_2.091 accompanied by a color change of reflected light. This phenomenon was not observed in ErH_1.95 where the molar volume varied smoothly up to the highest pressure. A pressure-induced transformation from hexagonal to cubic phase has been detected for erbium trihydride. For pure erbium metal, a transition from hexagonal to samarium structure has been revealed, confirming previously reported behavior.