Superconducting transition temperature Tc and normal-state resistivity as a function of oxygen content for hexagonal tungsten bronze Rb0.23WOy with 2.90 < y < 3.05 were obtained from transport measurements. It is remarkably interesting that Tc enhances about 50% and room-temperature resistivity increases about three orders of magnitude as oxygen content varies from 2.90 to 3.05. The low-temperature specific heat data indicate that the Einstein-like mode associated with Rb vibration has a dimensionality crossover from 3D to quasi-2D as oxygen content increases from 2.90 to 3.05. W L3-edge x-ray absorption spectra further show that W-O bond intensity gradually weakens as oxygen content increases, indicative of more oxygen disorder present in the oxygen-rich samples. The observed results strongly suggest that the local lattice distortion induced by oxygen disorder not only modulates Rb vibration, possibly coupled to electron-phonon interaction responsible for superconductivity, and also reduces the charge transfer between O 2p and W 5d orbital in the vicinity of y = 3.00. This scenario can possibly account for significant increases of Tc and normal-state resistivity of Rb0.23WOy as oxygen content slightly changes from 2.90 to 3.05.
Journal of Physics: Conference Series(JPCS) 150, 052141