FLUX-PINNING AND FLUX-CREEP IN MELT-TEXTURED (Y1-XPRX)BA2CU3O7-DELTA

Flux pinning and flux creep behaviour for the H\\c axis have been inve stigated on a set of MTG (Y1-xPrx)Ba2CU3O7-delta (X less than or equal to 0.08) samples. The critical current densities J(c), apparent pinni ng potential U-0 and effective activation energy U-eff(J, T) have bee n derived from the corresponding magnetic hysteresis and relaxation me asurements. The qualitative temperature and field dependences of the c ritical current densities are found to be unaffected by the Pr doping, up to the highest concentration level, in the present study. The temp erature-dependent profiles of the normalized relaxation rate S show si milar features, all including the initial linear and so-called plateau regions (roughly) with a peak interposed between them. Compared with the pure YBa2CU3O7-delta, the J(0), U-0, J and U-eff(J, T) values get enhanced for all the Pr-doped samples, with an optimal effect achieve d at Pr concentration around x = 0.05. A scaling relation U-eff(J, T) = U(i)G(T)F(J(i)/J) at a given magnetic field is used to analyse the U -eff(J, T) data, where U-i and J(i) are the scales of activation energ y and current density, respectively, and G(T) is either determined by a constructive scaling procedure or empirically chosen as G(T) = [1 - (T/T-r)(2)](3/2). The current-density-dependent behaviour of U-eff(J, T)/G(T), together with the observed S(T) feature and field-independent phenomenon of J(c)(H), is qualitatively consistent with the collectiv e-pinning theory. Possible pinning natures as well as a possible expla nation for the observed Pr concentration dependence of critical curren t density and activation energy are discussed, especially within the c ontext of pinning induced by the local lattice mismatch due to the Pr doping.