Fluctuation Conductivity and Phase Separation in Polycrystalline Y1-x Ce x Ba2Cu3O7-δ Superconductors

Fluctuations on the electrical conductivity of polycrystalline Y1-x Ce (x) Ba2Cu3O7-delta superconductors were investigated with Ce contents from x=0.01 up to 0.10. The results showed that the resistive transition proceeded in two stages, intragranular and intergranular, as indicated by the temperature derivative of the resistivity and verified by critical exponent analysis. Also, from the critical exponent analysis, we have observed a splitting of the pairing transition in all investigated samples. Our results strongly suggest that this pairing transition splitting is related to the occurrence of a phase separation associated with Ce doping. In the regime of near-zero resistance state, the temperature dependence of our data is consistent with a power-law behavior which is indicative of a phase transition from a paracoherent to a coherent state of the granular array.