Lattice dynamic stability and electronic structures of ternary hydrides La1-xYxH3 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 La 1Àx Y x H 3 , where 0 # x # 1, are determined to adopt tetragonal structures under high-pressure with the compositions La 0.8 Y 0.2 H 3 , La 0.75 Y 0.25 H 3 , and La 0.5 Y 0.5 H 3. 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 I4 1 /amd symmetry are semiconductors. The tetragonal La 0.5 Y 0.5 H 3 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.