Análise da transição de fase normal-supercondutora dos compósitos [{Y,Gd}Ba2Cu3O7-]1-y-[PrBa2Cu3O7-]y e {[YBa2Cu3O7-]0,95-[PrBa2Cu3O7-]0,05}1-x-{Ag}x

Abstract

In this work we analyzed the superconductor-normal transition of the composites [YBa2Cu3O7-]1-y-[PrBa2Cu3O7-]y with 0<y<0,1, {[YBa2Cu3O7-]0,95-[PrBa2Cu3O7-]0,05}1-x-{Ag}x with 0<x<0,2 and [GdBa2Cu3O7-]0,95-[PrBa2Cu3O7-]0,05. All samples were prepared for solid state reaction method. The X-ray analysis demonstrated that the diffraction patterns are identical to that to YBa2Cu3O7-superconductor. The electrical resistivity measurements as a function of temperature demonstrated that praseodymium causes two major effects: splitting in 𝑇𝑝1 and 𝑇𝑝2 of the pairing transition and increasing of separation between them mainly affecting the peak in 𝑇𝑝2. The analysis of thermodynamic fluctuations have enabled critical and Gaussians exponents demonstrating that transitions at 𝑇𝑝1 and 𝑇𝑝2 are genuinely superconducting and not only the effect of granularity of the samples. However, the doping 20% of Ag in the composite [YBa2Cu3O7-0,95-[PrBa2Cu3O7-0,05 quenched the second transition, indicating that its appearance should be possibly related to a third phase given by Y1-yPryBa2Cu3O7- in nanometric scale in the region intergrain. Magnetic measurements confirm the temperature values for the superconductor-normal transitions obtained by electrical resistivity measurements. Furthermore, it was found that the praseodymium increases electric current density. The composite [GdBa2Cu3O7-]0,95-[PrBa2Cu3O7-]0,05 presented double transition differently of sample Gd1-yPryBa2Cu3O7- reported in other studies, showing that the preparation of samples in the form of composite may exhibit different properties.