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 precursors YBa2Cu3O7 (Y123) + 0.24Y(2)O(3) + Ag2O with different amounts of Ag2O addition, grown at different furnace cooling rates, was analysed quantitatively by image processing of optical microscopy images. The critical average Ag concentration in the melt for the start and the steady state of Ag particle formation was estimated. A higher growth rate causes elongation and alignment of Ag particles in the growth direction. Type B monotectic crystallization was identified to take place in the hypermonotectic compositions. Monotectic and hypermonotectic types of Ag particles, which differ in size and morphology, were distinguished and the mechanisms of their formation proposed, taking into account the influence of both Ag and Y2O3 additions on the phase equilibria and considering a certain solubility of Ag in Y123.