Microwave surface impedance in a coaxial cavity as a material characterisation technique

Measurements of the surface resistance R_s of a number of modes of a coaxial cavity for which the center conductor is a BiSrCaCuO (BSCCO) rod have been made. Results for R_s(T) have allowed a quantitative estimate to be made of the proportions of two different phases present in this material. The variation of R_s(T) with applied DC magnetic field has also been measured for fields below about 1 mT. The results are interpreted in terms of two simple models for microwave loss in bulk high-temperature superconductors. It is concluded that the measurement of microwave surface impedance for high-temperature superconducting specimens can be used to make quantitative estimates of the proportions of various discrete superconducting phases, provided each has a distinguishably different T_c. The apparent concentration at the surface of the high-T_c phase, believed to be Bi₂Sr₂Ca₂Cu₃O₁₀, has not been previously reported and may have significance for applications of these materials