POTENTIAL OF POLY CRYSTALLINE Y BCO LAYERS FOR

The granular properties of polycrystalline YBCO layers can sensitively be characterized by their surface impedance, ZB. measured as a function of temperature, fre- quency and magnetic field. A model for &, based on grain- boundaries acting as resistively and inductively shunted Josephson junctions, allows a conclusive analysis of the field sensitivity of ZS and of the frequency dependence of the surface resistance. Preparatively controllable features like a large grain-size and a high degree of texturing are the basic requirements to exploit the full potential of such layers for high- and low-frequency applications. I. INTRODUCTION