Pressure induced impact on mechanical, electrical, optical, and thermal properties of Li4OX2 (X = Cl, Br and I): DFT study

We investigate the pressure effect on Li₄OX₂ (X = Cl, Br, and I) for the first time using DFT simulation. Li₄OCl₂ shows mechanical stability up to 8 GPa, whereas Li₄OBr₂ has stability up to 30 GPa pressure according to the Born stability criteria. In contrast, Li₄Ol₂ becomes unstable above 3.0 GPa pressure. Hence, anomalies were observed for Li₄OX₂ (X = Cl, Br, and I) solid electrolyte for elastic parameters, C_ij under pressure study. The elastic moduli are isotropic in the xy plane, conversely, along the xz and yz plane anisotropic behavior is observed. There is a band gap that exists at zero temperature and pressure. The contribution at the fermi level mainly comes from the O 2p states. The highest reflectivity (∼98 %) was observed for Li₄OCl₂ at ∼ 17 eV in the IR-visible-UV region showing that this material under study may be considered as a potential coating material to avoid solar heating. The smaller value of the volume thermal expansion coefficient for Li₄OCl₂ indicates stronger atomic bonding exists, which was also observed from the elastic parameter analysis.