Prediction and Synthesis of Dysprosium Hydride Phases at High Pressure.

Crystal structure prediction (CSP) methods recently proposed a series of new rare-earth (RE) hydrides at high pressures with novel crystal structures, unusual stoichiometries, and intriguing features such as high- superconductivity. RE trihydrides (REH) generally undergo a phase transition from ambient 6/ or 3̅1 to 3̅ at high pressure. This cubic REH (3̅) was considered to be a precursor to further synthesize RE polyhydrides such as YH, YH, YH, and CeH with higher hydrogen contents at higher pressures. However, the structural stability and equation of state (EOS) of any of the REH have not been fully investigated at sufficiently high pressures. This work presents high-pressure X-ray diffraction (XRD) measurements in a laser-heated diamond anvil cell up to 100 GPa and ab initio evolutionary CSP of stable phases of DyH up to 220 GPa. Experiments observed the 3̅ phase of DyH to be stable at pressures from 17 to 100 GPa and temperatures up to ∼2000 K. After complete decompression, the 3̅1 and 3̅ phases of DyH recovered under ambient conditions. Our calculations predicted a series of phases for DyH at high pressures with the structural phase transition sequence 3̅1 → 2 → 3̅ → → 6/ at 11, 35, 135, and 194 GPa, respectively. The predicted 3̅1 and 3̅ phases are consistent with experimental observations. Furthermore, electronic band structure calculations were carried out for the predicted phases of DyH, including the states, within the DFT+U approach. The inclusion of states shows significant changes in electronic properties, as more Dy states cross the Fermi level and overlap with H states. The structural phase transition from 3̅1 to 3̅ observed in DyH is systematically compared with other REH compounds at high pressures. The phase transition pressure in REH shows an inverse relation with the ionic radius of RE atoms.