Formation of NaCl-type monodeuteride LaD by the disproportionation reaction of LaD2

New Insights into Phase Separation of Cerium Hydrides under Pressure

We report theoretical calculations of the static ground-state structures and pressure-induced phase transformations of four cerium hydrides: CeH, CeH₂, CeH_2.5, and CeH₃. Under pressure, the experimental CaF₂-type structure of CeH₂ is likely to disproportionate to face-centered cubic (fcc) Ce and a cubic Pm3̅n (β-UH₃ type) structure of CeH₃ above 6 GPa. At further increasing pressures, fcc Ce will transform to a tetragonal I4/mmm structure above 12 GPa, while CeH₃ moves through the following sequence of phases: Pm3®n (β-UH₃ type) → Pm3̅n (A15 type) → R3®m; the corresponding transition pressures are calculated to be 10 and 70 GPa, respectively. The tetragonal I4₁/amd structure of CeH_2.5 has the similar decomposition as that of CeH₂. Finding this previously unreported pressure-induced decomposition of CeH₂ will pave the way for investigations on the nature of hydrogen-metal interactions.

Lattice dynamic stability and electronic structures of ternary hydrides La1−xYxH3via first-principles cluster expansion

Lanthanum hydride compounds LaH₃ become stabilized by yttrium substitution under the influence of moderate pressure. Novel materials with a wide range of changes in the structural properties as a function of hydrogen are investigated by means of the first-principles cluster expansion technique. Herein, the new compounds La_1−xY_xH₃, where 0 ≤ x ≤ 1, are determined to adopt tetragonal structures under high-pressure with the compositions La_0.8Y_0.2H₃, La_0.75Y_0.25H₃, and La_0.5Y_0.5H₃. The corresponding thermodynamic and dynamical stabilities of the predicted phases are confirmed by a series of calculations including, for example, phonon dispersion, electronic band structure, and other electronic characteristics. According to the band characteristics, all hydrides except that of I4₁/amd symmetry are semiconductors. The tetragonal La_0.5Y_0.5H₃ phase is found to become semi-metallic, as confirmed by adopting the modified Becke–Johnson exchange potential. The physical origins of the semiconductor properties in these stable hydrides are discussed in detail. Our findings provide a deeper insight into this class of rare-earth ternary hydrides.

Lanthanum hydride compound LaH₃ become stabilized by yttrium substitution under the influence of moderate pressure.