Superconducting transition temperature (T c) as a function of oxygen concentration for hexagonal rubidium tungsten bronzes Rb x WO y with 2.80 ≤ y ≤ 3.07 and x = 0.19, 0.23, and 0.27 has been systematically investigated. Three regions corresponding to T c < 2 K (denoted as superconductivity suppressed region), T c∼ 3 K (superconductivity uniform region) and T c > 3 K (superconductivity enhanced region) were identified in T c-y phase diagram for Rb 0.19WO y and Rb 0.23WO y. No superconductivity enhanced region was observed for Rb 0.27WO y. 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 T c-y phase diagram of Rb x WO y.
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