Compression behaviour of ErH ₃ synthesized at non Ambient Conditions

Abstract In recent times metal hydrides have reinvigorated the search for room temperature superconductivity owing to their intriguing physical properties. Among these, rare earth hydrides are unique due to their unequivocal properties related with hydrogen storage, potential for ambient superconductivity and switchable mirror technology. Towards this, we have synthesized higher erbium (Er) hydrides using pure Er metal and paraffin oil as an alternate hydrogen source by employing laser heated diamond anvil cell. Thus, synthesized hydride has been investigated using synchrotron-based angle dispersive x-ray diffraction (ADXRD) technique and Raman spectroscopy. At synthesized conditions (P = 36 GPa and T= 1800 K) the erbium hydride is found to be in face centred cubic (fcc) structure with stoichiometry as ErH 3 . Its compression behaviour has been studied up to 40 GPa during compression and decompression both. On decompression, it transforms to hexagonal close pack (hcp) structure of ErH 3 at ~ 5.2 GPa. The cubic phase is found to be partially recoverable on complete release of pressure. Equation of state for cubic phase has been established. The bulk modulus is determined to be 74±4 GPa for fcc phase. Furthermore, to study the possible chemical reaction of paraffin with Er and the effect of quasi hydrostaticity on its phase transition sequence, high pressure ADXRD measurements were carried out at room temperature. The detailed structural analysis establishes the phase transition sequence as hcp → hR24 (Sm-type structure) → dhcp beyond 9.6 GPa and across 23.8 GPa respectively.