Theoretical Investigation of the Phase Transition, Elastic and Superconductivity Properties of LaS Under Pressure

The first-principles method has been performed to investigate the phase transition, elastic, thermodynamic and superconductivity properties of lanthanum monosulphide (LaS) under pressure. A structural phase transition from the NaCl-type (B1) to CsCl-type (B2) structure is found to occur at around 16.8 GPa. The calculated ground state properties such as lattice constants, bulk modulus, and Debye temperatures are in good agreement with experimental data. Finally, the pressure dependence of the theoretical elastic constants and elastic modulus of LaS has been studied. The observations show that LaS is mechanically stable not only in B1 phase below 8.77 GPa but also in B2 phase under high pressure. LaS is ductile in B1 phase while brittle in B2 phase. The present observation of physical properties in B2 phase of LaS needs validation by future experimental.