Abstract
We report here a comparative study between the effects of Pr and Ca in place of Y on superconductivity and thermal fluctuation of the Y1-x M-x: 123 system with M = Pr and Ca and (0.00 < x < 0.50). Furthermore, some remarks on the hole carrier per Cu ions in high Tc superconductors are revaluated. It is found that numerical values of hole carrier per Cu ion based on M.R. Presland et al., Physica C 176, 95 (1991) disagree with those deduced from thermoelectric power (TEP) and some modifications to the M.R. Presland formula are necessary. On the other hand, the orthorhombic distortion is decreased, while the c-parameter is increased as x increases in Y1-x M-x: 123, but the rate of decrease/increase is dependent on the chosen M. The oxygen content has gradually decreased for the Ca series, whereas it is nearly unchanged (y = 6.94) for the Pr series. The doping density and the doping distance L are almost constant with increasing Pr up to 0.30 and then sharply decrease to Pr = 0.40. In contrast, a gradual sharp decrease in them is obtained for the Ca series. The spacing between Cu ions has gradually increased for the Pr series, but it has decreased for the Ca series. The critical temperature Tc is decreased as x increases for both series, but the rate of decrease is higher for Ca than for Pr as well as for hole carriers per Cu ion. The order parameter exponent (OPD) is two dimensional (2D) in and above the mean field region (MFR) as x increases up to 0.20 for both series. But with increasing x above 0.20, the OPD remains (2D) for the Ca series and becomes zero dimensional (0D) for the Pr series. While in the critical field region (CFR), the OPD is three dimensional (3D) for both series, but it becomes (2D) above x = 0.20 for the Pr series. The upper critical fields and critical currents are sharply increased for the Ca series up to x = 0.50, while they are slightly decreased by Pr up to 0.20 followed by an increase at 0.40. Our results are discussed in terms of the balance between the whole carriers generated/lost by substitution with those lost/introduced by oxygen vacancies in the Cu-O-2 planes. As compared to Pr, Ca makes Y: 123 more compact and has higher interlayer coupling, higher Ginzburg-Landau parameter and lower anisotropy, which as possible highlights the present work.