FLUCTUATION CONDUCTIVITY IN GRANULAR Tm1-xPrxBa2Cu3O7-δ SUPERCONDUCTOR

Abstract

We have studied fluctuations on the electrical conductivity in granular Tm 1-x Pr x Ba 2 Cu 3 O 7-δ (0 ≤ x ≤ 0.10) superconductors. Samples were prepared by the standard solid-state reaction technique. The results are described in terms of the temperature derivative of the resistivity, dρ/dT, and of the logarithmic temperature derivative of the conductivity, d ln (Δσ)/dT. The results show clearly that the resistive transition proceeds in two stages: intragranular and intergranular. Also, it was not observed in dρ/dT, near the transition, a structure consisting of two closely separated maxima, as seen in studies with other rare earth elements. Yet, the analysis of the conductivity in the normal phase has shown contributions from critical fluctuations and they were not affected by Pr doping. Below TC, on approaching the zero resistance state, our results show a power-law behavior with critical exponent s ≅ 4.1 for x = 0.00 and s ≅ 2.8 for x = 0.05 sample, indicating a phase transition from a paracoherent to a coherent state of the granular array. This behavior was not observed for x = 0.10 sample, showing that Pr affected the coherence transition.