Superconducting properties of the KxWO3 tetragonal tungsten bronze and the superconducting phase diagram of the tungsten bronze family

We report on the superconducting properties of the KxWO3 tetragonal tungsten bronze. The highest superconducting transition temperature (T-c = 2.1 K) was obtained for K0.38WO3. T-c decreases linearly with increasing K content. Using the measured values for the upper critical field H-c2 and the specific heat C, we estimate the orbital critical field H-c2(0), coherence length. xi(0), Debye temperature Theta(D), and coupling constant.lambda(e-p). The magnitude of the specific-heat jump at T-c suggests that the KxWO3 tetragonal tungsten bronze is a weakly coupled superconductor. The superconducting phase diagram of the doped tungsten bronze family is presented.