Properties of Rubidium Tungsten Bronzes RbxWOy

Superconducting transition temperature (Tc) as a function of oxygen concentration for hexagonal rubidium tungsten bronzes RbxWOy with 2.80 ≤ y ≤ 3.07 and x = 0.19, 0.23, and 0.27 has been systematically investigated. Three regions corresponding to Tc < 2 K (de-noted as superconductivity suppressed region), Tc ∼ 3 K (superconductivity uniform region) and Tc> 3 K (superconductivity enhanced region) were identified in Tc–y phase diagram for Rb0.19WOy and Rb0.23WOy. No superconductivity enhanced region was observed for Rb0.27WOy. The superconductivity suppressed region shifts toward higher oxygen content as rubidium concentration increases. The local ordering of the intercalated rubidium atoms might be responsible for the intriguing Tc–y phase diagram of RbxWOy. KEY WORDS: rubidium tungsten bronzes; oxygen concentration; superconductivity. 1