Structural and Optical Properties of Telluride Double PerovskiteCs₂TeBr₆ under High Pressure

Tellurium-based double perovskites offer the advantages of exceptional photoelectric properties, adjustable band gaps, and environmental friendliness, rendering them a promising class of light-absorbing materials. To further fine-tune the relevant attributes of these double perovskites, a comprehensive investigation of the structural-property relationship was conducted using a high-pressure diamond anvil cell (DAC) within in-situ high-pressure measurements. In this study, a representative tellurium-based double perovskite, Cs₂TeBr₆, was carefully investigated. The experimental findings reveal a notable structural transformation within the Cs₂TeBr₆ crystal lattice, transitioning from a cubic phase ($Fm \overline 3 m$) to a tetragonal phase (P4/mnc) in the pressure range of 0−51.0 GPa, which could be attributed to the tilting of the pressure-induced octahedron $\rm {TeBr}_6^{4-}$. Meanwhile, it is observed that the band gap of Cs₂TeBr₆ diminishes with increasing pressure under high pressure, exhibiting a turning point at approximately 14.0 GPa, coinciding with the onset of the structural phase transition. These findings contribute significantly to establishing the intricate correlation between the crystal structure and optical properties of Cs₂TeBr₆, thereby furnishing a valuable reference for precisely modulating the properties of tellurium-based perovskites.