Phase stability of some rare earth trihydrides under high pressure

Abstract

Phase stability of lanthanum, gadolinium and erbium trihydides have been studied at high pressure in diamond anvil cell. Raman high pressure studies up to 40 GPa of lanthanum trihydride and deuteride have shown more complex spectra than one can expect from the factor group analysis for stoichiometric LaH3. Our studies have shown that the stoichiometric lanthanum trihydride and deutride undergo pressure induced phase transformation presumably of hydrogen ordering origin.Investigations of the phase stability of erbium and gadolinium trihydrides have been performed using argon as pressure transmitting medium in Raman scattering method. The same medium has been used for X-ray diffraction analysis under pressure for erbium trihydride. Significant difference in the transition pressure as compared to earlier results obtained in quasi hydrostatic conditions has been noticed both in X-ray and Raman scattering measurements. Deviatoric stresses present in earlier nonhydrostatic measurements can be blamed for its discrepancy.