Temperature-dependent optical properties of CuFeO 2 through the structural phase transition.

Delafossite CuFeO 2 has recently attracted considerable attention because of its complex phase transitions and practical applications. A thorough understanding of the optical properties of CuFeO 2 is essential for its further exploration. In this paper, we investigated the temperature-dependent optical properties of CuFeO 2 single 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 the E g -symmetry 352 cm -1 mode and a hardening of the A 1g -symmetry 692 cm -1 mode 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 CuFeO 2 and provide key information for CuFeO 2 -based device design and fabrication.