Pressure-induced electronic transition in vacancy-ordered halide double perovskite Cs2TeBr6

We report high-pressure x-ray diffraction, Raman scattering, photoluminescence, and absorption measurements on vacancy-ordered halide double perovskite Cs2TeBr6. An electronic transition becomes apparent at around 2.3 GPa, characterized by anomalous behavior in the normalized pressure as a function of the Eulerian strain, a broad minimum in Raman linewidth, and a slope change in the linear pressure variation of a Raman mode frequency. The large compressibility and the observed anomalies in Raman scattering suggest that the material is soft and exhibits a strong electron–phonon coupling. The broad emission below the bandgap is attributed to the recombination of self-trapped excitons. The Cs2TeBr6 crystal, consisting of undistorted octahedra, exhibits substantial emission enhancement and bandgap narrowing under pressure. The electronic transition is further supported by the observed emission maximum and a small kink in the pressure variation of the bandgap at around 2.3 GPa.