Vacancy ordered double perovskites are outstanding materials for optoelectronic and renewable energy application. In this work, using the full-potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory (DFT) as implemented in the WIEN2k pakage, first principle calculations were performed to investigates the physical properties of vacancy order double perovskites under ambient and uniform pressure. Specifically, the structural, elastic, electronic, and optical properties of K₂TeCl₆ under diverse hydrostatic pressures ranging from 0 to 210 GPa are examined to vendicate the compounds superiority for useful applications. Under ambient pressure, we found a indirect band gap of 2.622 eV for K₂TeCl₆ and which reveals the compound semiconducting nature. Nevertheless, when pressure is increased (0 upto 210 GPa) the band gap narrows. In the pressure range elastic constant, cauchy’s pressure, poissons, and pughs ratio show the mechanical stability and ductile behaviour. Likewise, while maintaining mechanical stability, hydrostatic pressure significantly impacts elastic properties. The ductility and anisotropic behaviour of vacancy ordered double perovskite are intensified under applied and uniform pressure. The optical characteristics are analyzed for the incident photon energy range of 0-12 eV by computing dielectric constant, refractive index, optical condutivity, optical reflectivity and absorption coefficients which confirm that our compound is very suitable for device applications in the major parts of the spectrum (visible and ultraviolet). The optical functions are enhanced when pressure is applied, thus vindicating the chosen vacancy order in double perovskites as suitable for various optoelectronic devices operating in the visible and ultraviolet ranges.

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