High pressure phase transitions in the rare earth metal erbium to 151 GPa

Abstract

High pressure x-ray diffraction studies have been performed on the heavy rare earth metalerbium (Er) in a diamond anvil cell at room temperature to a pressure of 151 GPa and Erhas been compressed to 40% of its initial volume. The rare earth crystal structure sequence fcc (hcp: hexagonal close packed; fcc: face centered cubic; dhcp: double hcp) isobserved in Er below 58 GPa. We have carried out Rietveld refinement of crystalstructures in the pressure range between 58 GPa and 151 GPa. We have examinedvarious crystal structures that have been proposed for the distorted fcc (dfcc)phase and the post-dfcc phase in rare earth metals. We find that the hexagonalhR 24 structure is the best fit between 58 and 118 GPa. Above 118 GPa, a structural transformation fromhR 24 phase to a monoclinicC 2/m phase is observed witha volume change of − 1.9%. We have also established a clear trend for the pressure at which a post-dfcc phase isformed in rare earth metals and show that there is a monotonic increase in this pressurewith the filling of 4f shell.