The AgNO₃ route to the YBCO/Ag composite: Structural and electrical properties

In the present work we propose the use of AgNO₃ as the preparation route of the YBCO/Ag composite. First, AgNO₃ can be distributed more uniformly in the YBCO matrix in comparison with pure Ag. Secondly, the decomposition temperature of AgNO₃ (T_d = 444°C) is lower than the sintering temperature of YBCO and at the same time higher than the melting point of AgNO₃ (212°C). The activity of AgNO₃ during the early stages of the thermal treatment and its specific properties play an important role in shaping the morphology of the system that depends essentially on the Ag concentration. The molten AgNO₃ serves as a scavenger of the impurities on the grain surfaces and leads to their redistribution. This proves to have a profound effect on the properties of the intergrain boundaries, on the size of the grains, on their relative ordering and on the density of the composite. The concentration of silver regulates the dynamics of the recrystallization process and as a result determines the physical nature of the inter-and intragrain fluxon drift motion. Increasing the fraction of AgNO₃ in the composite from 15 wt%, through 30 wt% to 50 wt%, gives rise to a complex variation of its microstructure and of the related electrical characteristics.