Microwave properties of Ba $\mathsf{_{0.6}}$ K $\mathsf{_{0.4}}$ BiO $\mathsf{_3}$ crystals

We report on field-induced variations of the microwave surface resistance at 9.6 GHz of Ba 0.6 K0.4 BiO 3 crystals. Energy losses have been investigated as a function of the static magnetic field in the range of temperatures 4.2 K $\div T_c$ . By analyzing the experimental results in the framework of the Coffey and Clem model we determine the temperature dependence of the first-penetration field, upper critical field and depinning frequency. The results show that the pinning energy of this bismuthate superconductor is weaker than those of cuprates. Copyright Springer-Verlag Berlin/Heidelberg 2004