Mechanism and kinetics of sintering of nonstoichiometric Y-Ba-Cu-O powders

Using high-resolution optical and scanning electron microscopy with x-ray microanalysis at temperatures of 880 to 920°C, we studied the kinetics and mechanism of the formation of intergranular contacts during sintering of powder-substrate models and also studied the mechanism of shrinkage during sintering of Y-Ba-Cu-O compacts with a stoichiometric composition and two nonstoichiometric compositions, Y_0.95Ba₂Cu₃O_y and Y_1.05Ba₂Cu₃O_y. The formation and the shrinkage of powders of different compositions were found to be described by equations of different degrees, which points to different diffusion sintering mechanisms. Powders with stoichiometric and hyperstoichiometric compositions are sintered by a volume diffusion mechanism, which is controlled by the slowest ion, Y³⁺. Powders with a substoichiometric composition (Y-0.95) are sintered like a liquid phase, i.e., is controlled by diffusion through liquid or solid layers where new phases with higher diffusion coefficients are formed as a result of segregation effects.