Anomalous Metallic Cubic CsCuBr<sub>3</sub> Perovskites: Pressure- and Temperature-Driven Suppression of Jahn–Teller Distortion
Mei Li, Pengfei Shan, Bohao Zhao, Yiming Wang, Kejun Bu, Junlong Li, Hao Wang, Tingting Zhao, Shang Peng, Dongliang Yang, Sheng Jiang, Jiao An, Jinguang Cheng, Wenge Yang, Xujie Lü, Chuanlong Lin
Abstract
Distinct from traditional halide perovskites, which are based on main-group elements (e.g., Pb 2+, Sn 2+, Ge 2+ ) and are typically semiconducting, transition metals like Cu 2+ ─characterized by partially filled d-orbitals─offer unique advantages in modulating the electronic behavior of perovskite materials. However, the strong Jahn–Teller effect of Cu 2+ 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 CsCuBr 3 via a tailored structural design under high-temperature and high-pressure conditions. In situ synchrotron X-ray diffraction reveals that the orthorhombic nonperovskite CsCuBr 3 precursor (space group C 222 1 ) transforms into a cubic perovskite structure (space group Pm -3 m ) 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 Cu 2+, offering a promising strategy for the design of high-performance novel materials.