Structural studies of gadolinium at high pressure and temperature

Abstract

High pressure and high temperature angle-dispersive x-ray diffraction measurements on gadolinium were performed up to $93\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ and nearly $2500\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ using argon as pressure medium. Our room temperature measurements confirmed the transition pressures reported in a previous study carried out using nitrogen as pressure medium, solving former discrepancies found in the literature. A new phase was observed above $1200\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ between $39\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ and $52\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. Additionally, the structure of the previously observed dfcc and post-dfcc phases was determined, being the space group symmetry of the post-dfcc phase $(C2∕m)$, different from what was predicted before. Finally, the room temperature equation of state was determined for Gd and its pressure-temperature phase diagram redefined.