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

Abstract

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.