Growth related microstructure of Bridgman grown YBa2Cu3O7/Y2BaCuO5 single-grain bars

The microstructure of YBa2CU3O7 (123)/Y2BaCuO5 (211) single-grain bars grown by the Bridgman technique was studied by polarized light optical microscopy and image processing. For the first time, one c- and two a-growth sectors were microstructurally identified and the differences in their microstructure were compared. The subgrain structure of the growth sectors exhibits similar features as in the case of top seeded melt-grown (TSMG) single-grain samples. The realistic shape of the growing interface was drawn on the basis of a detailed microstructure analysis of the growth sectors. Quantitative measurements of the 211 particle volume fraction in the cross-section of the bar revealed higher 211 concentration at the end of the c-growth sector caused by pushing effect. Anisotropy of the 211 particle pushing is responsible for higher 211 concentration in the a-growth sectors than in the c-GS. However, this inhomogeneity of 211 concentration is much lower than that in the TSMG samples. Oscillations of 211 particle concentration developed in the c-growth sector were associated with temperature fluctuations at the growth front. All these findings are original and are essential in understanding superconducting and mechanical behaviour of the YBa2CU3O7/Y2BaCUO5 composite superconductors prepared by the Bridgman method.