Investigating the Effect of Hydrostatic Pressure on the Structural, Electronic, Mechanical, Lattice Dynamics and Optical Properties of the Cubic Perovskite RbTaO3: A DFT Approach

Abstract

Ab-initio calculations based on the spin-polarized density functional
theory (SP-DFT) are performed to examine the structural, mechanical,
electronic, lattice dynamic and optical properties of the cubic
perovskite RbTaO3 under pressure (0 – 200GPa). The study revealed
that the compound is neither ferromagnetic nor non-magnetic from the
lattice parameter-energy variation curve. The material is found to be
stable and brittle from mechanical stability conditions for cubic
structures. The results of the Zener anisotropy factor show that within
the pressure range of 0 – 40GPa, the compound is anisotropic while
above 40GPa, it portrays isotropic character. It was also observed that
it exhibits a semiconductor character as shown in the electronic band
structures and the influence of the application of pressure caused the
band gap transformation from an indirect band gap at 0GPa to a direct
band gap at 150GPa. The existence of this transformation in the
energy gap makes RbTaO3 a promising candidate for optoelectronic,
photovoltaic and photochemistry devices applications. From the
phonon dispersion curves, it is clear that the material is dynamically
unstable due to the presence of negative frequencies. The essential
optical functions such as refractive index ????(????), absorption coefficient
spectrum ????(????), reflectivity ????(????), electron energy-loss spectrum
????(????), the extinction coefficient ????(????)and optical conductivity were
investigated. The optical parameters demonstrate that cubic RbTaO3
is active in visible–ultraviolet regions.