João Frederico Haas Leandro Monteiro

Fluctuation-induced conductivity in melt-textured Pr-doped YBa2Cu3O7-δ composite superconductor

ABSTRACT In this study, the effects of thermal fluctuations on the electrical conductivity in melt-textured YBa2Cu3O7-δ, Y0.95Pr0.05Ba2Cu3O7-δ and (YBa2Cu3O7-δ)0.95–(PrBa2Cu3O7-δ)0.05 composite superconductor were considered. The composite superconductor samples were prepared through the top seeding method using melt-textured NdBa2Cu3O7-d seeds. The resistivity measurements were performed with a low-frequency, low-current AC technique in order to extract the temperature derivative and analyze the influence of the praseodymium ion on the normal superconductor transition and consequently on the fluctuation regimes. The results show that the resistive transition is a two-step process. In the normal phase, above the critical temperature, Gaussian and critical fluctuation regimes were identified, while below the critical temperature, in the regime near the approach to the zero-resistance state, the fluctuation conductivity diverges as expected in a paracoherent-coherent transition.

Fluctuation-induced conductivity and phase separation in composite samples (YBa2Cu3O7-δ)1−y–(PrBa2Cu3O7-δ)y

Fluctuation-induced conductivity in composite samples (YBa2Cu3O7-δ)1−y–(PrBa2Cu3O7-δ)y was investigated. The samples with were produced through the solid-state reaction method. Powder X-ray Rietveld analysis for the composites demonstrated that the patterns are identical to that of YBa2Cu3O7-δ. From the critical exponent analysis, it could be observed that the transport properties of composites are governed by the presence of two phases: YBa2Cu3O7-δ and PrBa2Cu3O7-δ. Splitting of the pairing transition was observed and two critical temperatures were identified, but only one is strongly affected by Pr. The composite structure can be thought as a three-dimensional grain percolation system with the structure of Pr-grain and Y-grain unit cell.