Keywords (Extracted from title, table of contents and abstract of thesis)
flux motion, electrical conduction, granular high tc superconductors, magnetic fields, ybco, bscco, flux flow, flux creep, flux pinning 
Abstract Experimental work has been carried out on YBCO and BSCCO based granular high Te superconductors to explore the mechanism of conduction in applied magnetic field. dc resistivity technique has beep employed to observe the details of dissipation, dependent and independent of the mutual orientation () of J and B. Both ZFC and FC dissipation have been studied. The p(())H.T, p(H,I).To and P(T,I)H,o measurements were taken in the field range 0 < H < 16 KOe and in the temperature range of 77K to 86K. The p( ()) data observed contained both angle independent and angle dependent dissipations. At fields H < H c1, the angle dependent dissipation is comparatively larger than the angle independent part and the case is opposite for fields H >> Hc1 (2  16 KOe). The angle dependence has a sin2() variation which is a typical signature of flux flow (Pff). This pff part varies with increasing fields according to a modified flux flow expression, in line with the reported microwave surface resistance data. We study in detail the variation of the modified flux flow (MFF) with temperature, and current. We find that the field dependent exponent in the MFF varies from being close to 1 to 0.4, with increasing degree of vortex disorder due to current or temperature. Similarity between the behavior of YBCO (at higher currents and temperatures) and that reported for BSCCO, is noted and explained. The field, current and temperature variation of angle independent part Pps has also been investigated. At relatively low values of current and at higher temperatures, the data follows an approximated Amegaokar Halperin expression approximated for small value of argument, The field dependence of r has been found to be HI/3 consistent with some previously reported results obtained by others in the low field region. At low angles the angular part of the dissipation shows deviations from sin20, as well as hysteresis. This low angle anomaly was thoroughly studied at different currents, fields and temperatures and interpreted as an effect of Lorentz force mediated flux redistribution between inter and intragrain regions. A magnetization model was developed to incorporate both the equilibrium and non equilibrium parts of magnetization in the granular samples. The data were fit to M(H) and the values of He2(T) obtained. These values of Mequil were used to fit the pff(H) data.
