Superconducting Properties of the K$_{x}$WO$_{3}$ Tetragonal Tungsten Bronze and the Superconducting Phase Diagram of the Tungsten Bronze Family

Abstract: We report the superconducting properties of the K${x}$WO${3}$ tetragonal tungsten bronze. The highest superconducting transition temperature ($T_{c}=2.1$K) was obtained for K${0.38}$WO${3}$. $T_{c}$ 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 $\lambda _{ep}$. The magnitude of the specific heat jump at $T{c}$ suggests that the K${x}$WO${3}$ tetragonal tungsten bronze is a weakly-coupled superconductor. The superconducting phase diagram of the doped tungsten bronze family is presented.