Characterisation of some properties of the YBa2Cu3O7-σ/Ag composites prepared by different methods

In this master thesis it was prepared YBa2Cu3O7-σ-Ag (x = 5 - 80 wt %) samples by different preparation methods. X-ray powder diffraction achieves the presence of superconducting YBa2Cu3O7-σ phase and the phase of pure silver. X=ray powder diffraction patterns shows decrease of content of YBa2Cu3O7-σ phase with increasing with content silver. Measurements of critical temperature shows then in lower content of silver (5-40 wt %), silver does not influence significance on critical temperature. In higher content of Ag (60, 80 wt %) silver completely destroy superconductivity and samples shows normal-state conductivity. In YBa2Cu3O7-σ/Ag system, the melting point of pure silver (961 grad C) decreases to 954 grad C. Silver could be doped in the grains rather than precipitated at the grains in the samples prepared at a relatively lower sintering temperature. Sintering at higher temperature results in diffusing of most of Ag to grain boundaries causing the decrease of normal-state resistivity and increase of the critical current without significant effect on the critical temperature. (author)