Hydrostatic pressure on XLiH3 (X = Ba, Sr, Ca) perovskite hydrides: An insight into structural, thermo-elastic and ultrasonic properties through first-principles investigation

Abstract

Density functional theory based first-principles investigation on structural, elastic, ultrasonic and thermodynamic properties of cubic perovskite hydrides XLiH3 (X = Ba, Sr, Ca) at ambient and high pressures is reported in this study. The evaluated structural parameters of the titled hydrides are in agreement with available experimental and theoretical results. The influences of hydrostatic pressure on single-crystal and subsequent polycrystalline elastic parameters along with different mechanical properties are discussed in detail. The calculated ultrasonic velocities, Debye temperatures (ΘD) and minimum thermal conductivities (κmin) increase monotonically with increasing pressure for each hydride. The increase of both ΘD and κmin along BaLiH3→SrLiH3→CaLiH3, and the estimated Vickers hardness indicate that CaLiH3 is the hardest among these hydrides. The relatively low values of κmin in the ground state suggest that these compounds are promising to be used as thermal insulators. Various macroscopic thermodynamic parameters such as bulk modulus, heat capacity, thermal expansion coefficient and entropy as a function of temperature and pressure are also predicted using the quasi-harmonic Debye model and their implications are elucidated.