Anomalous Metallic Cubic CsCuBr3 Perovskites: Pressure- and Temperature-Driven Suppression of Jahn–Teller Distortion

Abstract

Distinct from traditional halide perovskites, which are based on main-group elements (e.g., Pb2+, Sn2+, Ge2+) and are typically semiconducting, transition metals like Cu2+─characterized by partially filled d-orbitals─offer unique advantages in modulating the electronic behavior of perovskite materials. However, the strong Jahn–Teller effect of Cu2+ makes it a significant challenge for stabilizing a robust three-dimensional perovskite framework. Herein, we report the first synthesis of a metallic cubic perovskite phase of CsCuBr3 via a tailored structural design under high-temperature and high-pressure conditions. In situ synchrotron X-ray diffraction reveals that the orthorhombic nonperovskite CsCuBr3 precursor (space group C2221) transforms into a cubic perovskite structure (space group Pm-3m) featuring an undistorted corner-sharing octahedral framework at ∼22 GPa and ∼603 K. The perovskite structure remains stable at pressure down to 4.3 GPa at room temperature, while at low temperatures below 50 K, it may be recovered to ambient pressure. Notably, the structure lacks both the expected luminescence and a distinct absorption edge, instead exhibiting a metallic behavior, as confirmed by temperature-dependent resistance measurements. Electronic structure calculations at 22.4 GPa and 0 K further reveal pronounced hybridization between the Cu-3d and Br-4p orbitals near the Fermi level, leading to an enhanced orbital degeneracy and electron delocalization. These findings demonstrate that the lattice contraction effectively suppresses the strong Jahn–Teller distortion intrinsic to Cu2+, offering a promising strategy for the design of high-performance novel materials.