Synthesis, Structure, and Properties of CuBiSeCl₂: A Chalcohalide Material with Low Thermal Conductivity

Mixed anion halide-chalcogenide materials have recently attracted attention for a variety of applications, owing to their desirable optoelectronic properties. We report the synthesis of a previously unreported mixed-metal chalcohalide material, CuBiSeCl₂ (Pnma), accessed through a simple, low-temperature solid-state route. The physical structure is characterized through single-crystal X-ray diffraction and reveals significant Cu displacement within the CuSe₂Cl₄ octahedra. The electronic structure of CuBiSeCl₂ is investigated computationally, which indicates highly anisotropic charge carrier effective masses, and by experimental verification using X-ray photoelectron spectroscopy, which reveals a valence band dominated by Cu orbitals. The band gap is measured to be 1.33(2) eV, a suitable value for solar absorption applications. The electronic and thermal properties, including resistivity, Seebeck coefficient, thermal conductivity, and heat capacity, are also measured, and it is found that CuBiSeCl₂ exhibits a low room temperature thermal conductivity of 0.27(4) W K^-1 m^-1, realized through modifications to the phonon landscape through increased bonding anisotropy.