Investigation of external isotropic pressure effect on widening of bandgap, mechanical, thermodynamic, and optical properties of rubidium niobate using first-principles calculations for photocatalytic application

In this research, the optical, thermodynamic, mechanical, structural, and electronic properties of the rubidium niobate have been studied under the effect of pressure using first-principles calculations. The GGA-PBE approach in CASTEP is employed to explore the features of cubic crystal structures. It was observed that the energy bandgap rises from 1.443 to 1.973 eV and also shows indirect semiconductor nature at all pressures. During calculations, it was noted that it retains the cubic structure with decreasing lattice parameters from 4.073 to 3.684 angstrom. The pressure reduces the contribution of states/eV which take part in the formation of valence band and conduction band. Furthermore, it is mechanically stable according to Born stability criteria and has anisotropic nature because the anisotropic factor is unity. The Pugh's ratio and Poisson scale criteria indicate that it transforms from brittle to ductile nature. Cauchy pressure ranges from - 28.63 to 132.39 GPa, therefore it's non-metallic at low pressures and metallic at high pressures. The Vicker's hardness standards suggests that its hardness transforms from super hard to ultra-hard with rising trend from 42.24 to 139.61 GPa. Furthermore, the Debye temperature, thermal conductivity, and melting temperature increase from 647.43 to 846.45, 2.51 to 4.19, 2598.45-7064.58, respectively. Comprehensive investigation of optical features under pressure demonstrates that strong peaks of optical properties correspond to the ultraviolet spectrum region with a small shift of curves towards higher energies. Therefore, the examination suggests that the under-study material is a potential candidate for long-term photocatalytic activity.