Surface resistance of bulk and thick film YBa2Cu3 Ox/ss

The surface resistance R_s of YBa₂Cu₃ O₇ (YBCO) has been measured by means of a coaxial method using a copper outer shield and an HTS (high-temperature superconductor) central conductor as well as by means of an all-YBCO TE ₀₁₁, cavity. The microstructure of the ceramic deliberately altered so that variables such as starting powder size and phase purity, ceramic density, phase composition, grain size, and number of grain boundaries can be evaluated. A number of experiments have been conducted so that the variables chosen might be studied independently. The results show that R_s varies in a complex manner according to the microstructure and that as sintered grain size is reduced to a certain size the R_s is reduced. Further decreases in grain size are associated with an increase in the number of grain boundaries and an increase in the R_s, suggesting that grain boundary detritus and grain boundaries themselves are sources of loss. The R_s is also highly dependent oil crystallographic orientation, and examples are given to show that R_s diminishes in c-axis-oriented YBCO thick films