Structural distortion and electronic states of Rb doped WO₃ by X-ray absorption spectroscopy

Rubidium tungsten bronzes (Rb_xWO₃) have recently attracted much attention due to their intriguing phenomena, such as complex structural phase transitions, strong electron-phonon coupling, and superconducting properties. This study investigates the local atomic and electronic structures of Rb_xWO₃ (0.17 ≤ x ≤ 0.33). X-ray powder diffraction patterns showed a hexagonal tungsten bronze (HTB) phase. X-ray absorption spectra (XAS) at the W L₃-edge and Rb K-edge of Rb_xWO₃ were carried out. The XAS analysis indicated a local distorted WO₆ octahedron which leads to a splitting of e_g and t_2g energy states in the tungsten 5d orbital and this splitting of energy levels exhibited an asymmetrical behavior at x = 0.23 and 0.27. Overall analysis revealed a distortion of local atomic structure of the WO₆ octahedra by rubidium doping, leading to the modification of the electronic structures of e_g and t_2g states in the tungsten 5d orbital, thereby accounting for the property changes in CDW formation and superconducting transition temperature of these materials.