CRITICAL CURRENTS AND CURRENT-VOLTAGE CHARACTERISTICS OF HIGH-TEMPERATURE SUPERCONDUCTING CERAMICS

We discuss problems related to the ''arrangement'' and properties of t hose elements of the granular structure of HTSC ceramics (with an emph asis on the ceramics of the YBa2Cu3O composition) which define the cri tical currents and current-voltage characteristics of ceramic material s. The basis element of this sort are intergranular boundaries. In mat erials of practical interest their predominant role as ''weak'' sites (that is, areas with a low critical current density) is to lower criti cal current density of ceramics. For modeling purposes ceramics can be regarded as Josephson media, that is as sets of superconducting grain s interconnected by Josephson Junctions. This model provides a means o f describing a good number of properties of superconducting ceramics w ithout going into detail about the specific genesis and ''arrangement' ' of weak intergranular links. In this way we discuss the critical cur rent and current-voltage characteristics of HTSC-ceramics and their de pendencies on temperature, magnetic field and pressure.