Lattice dynamic stability and electronic structures of ternary hydrides La1-x Y x H3 via 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 La1-x Y x H3, where 0 ≤ x ≤ 1, are determined to adopt tetragonal structures under high-pressure with the compositions La0.8Y0.2H3, La0.75Y0.25H3, and La0.5Y0.5H3. 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 La0.5Y0.5H3 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.