Fluctuation‐induced conductivity of (YCe)Ba 2 Cu 3 O 7– δ superconductor

Systematic measurements of the in‐plane and out‐of‐plane in conductivity fluctuations have been used to investigate the role of the cerium ion on the splitting of the pairing transition. This splitting, associated with a phase separation, was firstly observed in single crystals and polycrystalline samples of Y 1– x Pr x Ba 2 Cu 3 O 7– δ . Considering that Ce is the rare‐earth element most easily ionized to the +4 state and that in melt‐textured sample, it is possible to observe anisotropic effects, we examined the effect of this ion in the Y 1– x Ce x Ba 2 Cu 3 O 7– δ compound. We prepared three different samples: polycrystalline, pure melt‐textured and Ce‐doped melt‐textured. Melt‐textured samples were prepared using the top‐seeding growth technique and the polycrystalline sample by the standard solid‐state reaction technique. The samples were characterized by X‐ray diffraction, scanning electron microscopy (SEM) and electrical resistivity. To identify power‐law divergences in the conductivity, the results were analyzed in terms of the temperature derivative of the resistivity ( ${\rm d}\rho /{\rm d}T$ ) and of the logarithmic temperature derivative of the conductivity ( ${-} {\rm d}{\ln} (\Delta \sigma )/{\rm d}T$ ). In the normal phase, Gaussian and critical regimes were clearly seen for melt‐textured samples and no important differences between pure and Ce‐doped samples were observed. On the other hand, for the polycrystalline sample and from the critical exponent analysis, a splitting of the pairing transition was clearly observed. It is suggested that the occurrence of a phase separation and its association with Ce doping as already observed for Pr‐doped samples.