Influence of Ag addition on crystallization and microstructure of melt-grown single-grain YBa2Cu3O7 bulk superconductors

The microstructure of YBaCuO/Ag composite materials prepared from precursor s YBa2Cu3O7 (Y123) + 0.24Y(2)O(3) + Ag2O with different amounts of Ag2O add ition, grown at different furnace cooling rates, was analysed quantitativel y by image processing of optical microscopy images. The critical average Ag concentration in the melt for the start and the steady state of Ag particl e formation was estimated. A higher growth rate causes elongation and align ment of Ag particles in the growth direction. Type B monotectic crystalliza tion was identified to take place in the hypermonotectic compositions. Mono tectic and hypermonotectic types of Ag particles, which differ in size and morphology, were distinguished and the mechanisms of their formation propos ed, taking into account the influence of both Ag and Y2O3 additions on the phase equilibria and considering a certain solubility of Ag in Y123.