Síntese e caracterização do supercondutor Y3Ba5Cu8O18

Abstract

In this approach an experimental study of the electrical and magnetic properties of the superconducting Y3Ba5Cu8O18 (Y358) is presented. For this study was prepared a polycrystalline sample of Y358 by solid state reaction, which was structurally characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy (EDS). The results obtained by these techniques showed the granular feature of our sample. In order to study the magnetic properties, magnetization measurements following the ZFC and FC procedures were performed from zero to 10 kOe. With the results of magnetization was possible to determine the magnetic irreversibility line (LIM), which had its behavior described by the superconducting glass model, showing a crossover of the Almeida-Thouless regime (AT) to the Gabay-Toulouse regime (GT), for H = 1 kOe. The LIM functionality described by GT regime persisted until the high value of 10 kOe. The electrical properties were studied by magnetoresistance measurements, which were performed in the magnetic field range between 0 and 10 kOe. The results showed a strong reduction in the zero resistance temperature (TCO) when the magnetic field is increased, as well as a reduction in the critical temperature to the superconducting state. From the derivative of the resistivity with the temperature was observed the presence of two peaks, indicating that the resistive transition of the sample is a process that occurs in two steps. The results obtained with the magnetization and magnetoresistance allowed to correlate the zero resistivity and the magnetic irreversibility, which showed that the zero resistance temperature occurs for values well below of the irreversible limit, which is expected for a granular system. Furthermore, the thermodynamic fluctuations in the electrical conductivity were studied. In normal phase Gaussian regimes, critical and supercritical regimes were identified, while in the approximation of the zero resistance state the results showed a regime in power law corresponding to the typical paracoherent-coherent phase transition of granular systems. The supercritical regime presented a robust characteristic for magnetic fields up to 2.5 kOe. The other power low regimes showed a considerable stability with the application of magnetic fields up to 10 kOe.