New Insights into Phase Separation of Cerium Hydrides under Pressure

[Image: see text] We report theoretical calculations of the static ground-state structures and pressure-induced phase transformations of four cerium hydrides: CeH, CeH(2), CeH(2.5), and CeH(3). Under pressure, the experimental CaF(2)-type structure of CeH(2) is likely to disproportionate to face-centered cubic (fcc) Ce and a cubic Pm3̅n (β-UH(3) type) structure of CeH(3) above 6 GPa. At further increasing pressures, fcc Ce will transform to a tetragonal I4/mmm structure above 12 GPa, while CeH(3) moves through the following sequence of phases: Pm3®n (β-UH(3) type) → Pm3̅n (A15 type) → R3®m; the corresponding transition pressures are calculated to be 10 and 70 GPa, respectively. The tetragonal I4(1)/amd structure of CeH(2.5) has the similar decomposition as that of CeH(2). Finding this previously unreported pressure-induced decomposition of CeH(2) will pave the way for investigations on the nature of hydrogen–metal interactions.