Pressure-Induced Structural and Electronic Transition in Sr₂ZnWO₆ Double Perovskite

High-pressure structural and electrical properties of Sr₂ZnWO₆ double perovskite were investigated using in situ angle-dispersive synchrotron X-ray diffraction (XRD), Raman, and alternating current (AC) impedance spectroscopy. A structural transition from monoclinic (P2₁/n) to triclinic (P1̅) phase around 9 GPa was observed due to the pressure-induced distortion of (W, Zn)­O₆ octahedron. In situ high-pressure Raman spectroscopy showed the increasing interaction among O–W–O in WO₆ octahedron with pressure and a transition pressure consistent with the XRD results. From the AC impedance spectroscopy measurements, the resistivity increased steeply by ∼1 order of magnitude around 11 GPa, indicating an electronic transition accompanying the symmetry change. The increase in the interaction among O–W–O enhances the attraction of O^2– electrons toward W⁶⁺, thus increasing the covalence, which in turn lowers the charge transfer energy between O^2– and W⁶⁺ and induces the resistivity increase under high pressure.