Surface resistance of bulk and thick film YBa/sub 2/Cu/sub 3/O/sub x//ss

Abstract

The surface resistance R/sub s/ of YBa/sub 2/Cu/sub 3/O/sub 7/ (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/sub 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/sub s/ varies in a complex manner according to the microstructure and that as sintered grain size is reduced to a certain size the R/sub 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/sub s/, suggesting that grain boundary detritus and grain boundaries themselves are sources of loss. The R/sub s/ is also highly dependent oil crystallographic orientation, and examples are given to show that R/sub s/ diminishes in c-axis-oriented YBCO thick films.