A comparative study of grain boundary structure and critical current density in 123-YBaCuO, 2212-BiSrCaCuO and 2223-TlBaCaCuO high temperature superconductors

Abstract

Abstract A systematic study of the structure of symmetric and asymmetric tilt boundaries in 123-YBaCuO and 2223-TlBaCaCuO superconductors is carried out using geometrical modelling. The coincidence site lattice (CSL) configurations of the a−b and a−c type grain boundaries with the CSL unit cell are presented and the important differences between them pointed out. The fraction of the continuous superconducting CuO planes and the charge associated with the boundary void configurations are determined as a function of the misorientation angle of the a−b boundaries. Two different orientations in the a−c -type boundaries arising from the interchange of the a and c lattice directions are described. The differences in the a−c -type boundaries in 123-YBaCuO and 2223-TlBaCaCuO are discussed with special reference to the continuity of the CuO planes and the current-carrying capacity. The geometrical modelling is also extended to describe the distortions, the unbalanced charge and the continuity of the CuO planes in the asymmetric tilt boundaries and disclinations in the 123-YBaCuO system. The critical current density associated with the boundaries is studied in terms of tunnelling of superconductor pairs through the coalesced regions containing distortions. The critical current density obtained in terms of the depression of the order parameter, the width and the coalesced region of the boundary is found to agree with the experimental observations. Specifically, the temperature dependence of the critical current density is explained in terms of the variations in the order parameter and the transmission coefficient. Most importantly, the intergrain critical current density is found to decrease with the misorientation angle, which is in good agreement with previous experimental observations.