Etude des propriétés physiques des céramiques supraconductrices dopées

Abstract

In order to study the effect of doping on the physical properties of superconducting YBa2Cu3O7-δ ceramic compound in which Cu was substituted by: Ni, Ag, Mn and Co. We have prepared our samples from carbonate BaCO3, oxides Y2O3, CuO, MnO2 and CoO and AgNO3, by the solid state reaction method. The samples were then characterized by beams of the techniques of X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersive (EDX) analysis, Raman spectroscopy, electrical resistivity and DC susceptibility measurements. The analysis of the XRD shows the presence of the orthorhombic major phase YBa2Cu3O7-δ (YBCO) and the secondary phases BaCuO2 (Y011) and Y2BaCuO5 (Y211). No phase transition occurred at the atomic concentration dopants 0  x  4%. The refinement by Winplotr and Dicvol04 programs shows that the cell parameters have been affected, due to the incorporation of the dopant into the cell. The SEM micrographs show that the incorporation of all the dopants induces in generally a thinner grain with a porous structure, except for some samples that have large grains. The EDX analysis confirms the incorporation of the dopants into the grains. This analysis reveals also that the distribution dopants in the samples is not homogenous. These analyses allow to suggest the possibility of substitution of Ag and Mn in barium sites and copper chain sites Cu(1). Measurements of DC magnetic susceptibility and electrical resistivity reveal a decrease in TCon as a function of the doping rate. This decrease is more probably due to the change in carrier density, CuO2 plane disorder and overall oxygen content, for nickel and manganese. This is not the case for the silver doped sample with 0.5 at.% which has a greater TC than the pure sample. The results of the Raman spectroscopy confirm the presence of the YBCO phase with the two secondary Y011 and Y211 phases. The incorporation of the dopant in the grains in the Cu (2) planar sites, and the contraction of the parameter c. The recorded five active modes confirm that the structure is orthorhombic for all the samples and the phase transition has not take place in the interval 0  x  4%.