Microwave properties of Ba <InlineEquation ID="Equ1"> <EquationSource Format="TEX">$\mathsf{_{0.6}}$</EquationSource> </InlineEquation>K <InlineEquation ID="Equ2"> <EquationSource Format="TEX">$\mathsf{_{0.4}}$</EquationSource> </InlineEquation>BiO<InlineEquation ID="Equ3"> <EquationSource Format="TEX">$\mathsf{_3}$</EquationSource> </InlineEquation> crystals

We report on field-induced variations of the microwave surface resistance at 9.6 GHz of Ba<Subscript>0.6</Subscript>K<Subscript>0.4</Subscript>BiO<Subscript>3</Su bscript> crystals. Energy losses have been investigated as a function of the static magnetic field in the range of temperatures 4.2 K <InlineEquation ID="Equ4"> <EquationSource Format="TEX">$\div T_c$</EquationSource> </InlineEquation>. 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