Effect of Ag2O addition on the AC losses of Bi-(Pb)-Sr-Ca-Cu-O superconductors

SUMMARY Effect of Ag2O Addition on the AC Losses of Bi-(Pb)-Sr-Ca~Cu-0 Superconductors In this thesis, the effects of Ag20 addition on AC losses of Bi-(Pb)-Sr-Ca-Cu-0 system have been investigated by means of AC susceptibility measurements and theoretical analysis. Dependence on magnetic field and frequency of AC susceptibility and losses have been studied. From the examinations of the experimental results for the samples, Ag20 addition was seen to change the pattern of frequency dependent AC susceptibility and field dependent AC susceptibility curves. Experimental results are qualitatively discusssed in the framework of the critical state model. Intergranular critical current density was found to decrease with increased amount of Ag20 addition (0, 15, 30 wt %). The volume fractions of the grains were estimated as a function of both Ag20 amount and field amplitudes. The expression for the critical current density given by Jcm(T) = -4 aJ TY 1- T V cm J is used in critical state calculations. Where a 0 denotes the pinning strength parameter at T=0, n and p represent the field and temperature dependence of the intergranular critical current density, respectively. The field and temperature dependence (Bn and p) of the intergranular critical current density for each sample were determined from the comparison of the experimental and calculated curves. The field exponent n, volume fractions of the grains fg, temperature exponent p, were found to increase with increasing amount of Ag20 addition. Experimental isothermal hysteresis losses as a function of field amplitude are reproduced quite well by calculation using the same fitting parameters as that for %"(T) data. Keywords: Ag20 Addition, Bi-(Pb)-Sr-Ca-Cu-0 Superconductor, AC Losses, Critical Current Density VI