MEASUREMENT OF THE MICROWAVE CONDUCTIVITIES OF HIGH-T(C) SUPERCONDUCTING POWDERS

Analysis and justification is given for a method of obtaining the complex anisotropic microwave conductivity sigma of magnetically aligned high-T(c) superconducting powders, from observations of the changes in frequency and bandwidth of a strip line resonator which occur when the sample is inserted near an antinode of RF magnetic field. In spite of difficulties in determining the shapes and size distribution of the particles, the method has a relative accuracy of about +/-2%, and for ceramic superconductors has a number of advantages over the traditional method of determining sigma from measurements of the surface impedance. Powders prepared by grinding give consistent results, comparable with those obtained by traditional methods on the best single crystals.