Temperature-dependent optical properties of CuFeO₂through the structural phase transition

Delafossite CuFeO₂has recently attracted considerable attention because of its complex phase transitions and practical applications. A thorough understanding of the optical properties of CuFeO₂is essential for its further exploration. In this paper, we investigated the temperature-dependent optical properties of CuFeO₂single crystals through Raman scattering spectroscopy and spectroscopic ellipsometry. The room temperature Raman scattering spectrum exhibited six phonon modes at approximately 352, 509, 692, 1000, 1052, and 1171 cm⁻¹. Upon cooling across 11 K, which is the rhombohedral to monoclinic structural phase transition temperature, a softening of theE_g-symmetry 352 cm⁻¹mode and a hardening of theA_1g-symmetry 692 cm⁻¹mode were observed. Moreover, analysis of the temperature-dependent real part of the dielectric function and direct band gap revealed anomalies at 11 K. These results demonstrate a profound connection between the structural phase transition, lattice dynamics, and electronic structure of CuFeO₂and provide key information for CuFeO₂-based device design and fabrication.