Crystal structure and superconductivity of rubidium tungsten bronzes RbxWO3 prepared by a hybrid microwave method

The rubidium tungsten bronzes RbxWO3 have been prepared from Rb2CO3, WO3 and W powders using hybrid microwave method. The single hexagonal phase samples can be obtained as actual rubidium content x in the range of 0.21–0.33, and their lattice parameters a and c linearly drop and rise with the increase of rubidium content respectively. For samples with x = 0.14, 0.16, 0.18, the superconducting transition temperature Tc from resistivity measurements does not change with the rubidium content, while Tc from susceptibility measurements shows a decrease from 5.3 K for x = 0.14 to 4.8 K for x = 0.18. The charge density wave (CDW) transition appears in Rb0.21WO3, Rb0.23WO3 and Rb0.25WO3 at about 200–260 K. The CDW transition is most obvious in Rb0.23WO3 which shows the lowest degree of crystallization among the samples.