Potential of polycrystalline YBCO layers for applications

The granular properties of polycrystalline YBCO layers are characterized by their surface impedance, Z/sub s/, measured as a function of temperature, frequency and magnetic field. A model for Z/sub s/, based on grain-boundaries acting as resistively and inductively shunted Josephson junctions, is used for a conclusive analysis of the field sensitivity of Z/sub s/ and of the frequency dependence of the surface resistance. It is shown that reducing the granular character of polycrystalline samples leads to a lower absolute level and to a stronger frequency dependence of R/sub s/. As a result, the frequency-dependent improvement r=R/sub s/(Cu)/R/sub s/(YBCO), as well as the frequency at which r=1, can be increased. >