Exploration of pressure induced phase transitions and thermo-mechanical properties in LuX (X=As, Sb, Bi)

Abstract

This paper reports the detailed first-principle calculations carried out to investigate the high pressure structural phase stability of lutetium pnictides (LuX, where X = As, Sb and Bi) up to 200 GPa. All of these compounds crystallize in the rocksalt type structure (B1 phase) at ambient condition. In LuAs our calculations suggest the occurrence of orthorhombic structure (Cmcm space group) at ∼ 53 GPa, which is close to the experimentally reported transition pressure of ∼57 GPa to an unresolved structure. This orthorhombic phase further transforms to a tetragonal structure (space group I4/amd) at ∼ 67 GPa. In LuSb and LuBi, B1 phase directly transforms to I4/amd structure at ∼20 GPa and ∼17 GPa, respectively. Upon further compression, in case of LuAs and LuSb, the I4/amd phase remains stable up to 200 GPa, however, in LuBi this tetragonal phase transforms to another tetragonal structure (space group P4/mmm). Also, using quasi-harmonic approximation, the temperature variation of various thermo-physical quantities, namely, bulk modulus, volume, volume thermal expansion coefficient, heat capacity, and Gruneisen parameter of these compounds for the ambient B1 phase have been determined in the present study.