Relation between change of porosity and parameters of grains during annealing of the superconducting ceramics YBa2Cu3O7−x

The correlation between changes of porosity and the parameters of grains was studied during the annealing of fine-grained ceramics Y123 with various amounts of phase Y211 in the temperature range 900–990 °C with the aim of revealing the mechanism of pore healing. Y123 grains retain their lamellar shape within the temperature range of annealing. Authenticated cases of growth of grains towards pores via local bulging of a plane surface have not been revealed. Healing of pores is observed only in the temperature range 900–975 °C. The most complete pore healing takes place when secondary recrystallization occurs in the sample with the resulting formation of the microstructure possessing wide distributions of grain sizes and grain aspect ratios. 2D simulations have shown that Y123 behaves like a free-flowing body. During the growth of a microstructure with a large variety of grain sizes and aspect ratios, the grains better fit each other, and pores decrease.