INFLUENCE OF Y2BACUO5 PARTICLES ON THE MICROSTRUCTURE OF YBA2CU3O7-X (123)-Y2BACUO5(211) MELT-TEXTURED SUPERCONDUCTORS

The paper is devoted to the microstructural defects in melt-processed TBaCuO which can be active either as magnetic-flux-pinning centers or weak links. The influence of 211 particles in 123-211 melt-textured bulk superconductors on the microstructural features such as microcracking, subgrains, twins, and twin complexes was studied by polarized light microscopy. The observed linear dependence between a-b microcrack spacing, and l(c), and d(211). V-123/V-211 (d(211) means 211 particle size, V-123 means 123 volume fraction, V-211 means 211 volume fraction) proves that the microcracking process can be described under the framework of a model devised for the multiple failure of a unidirectional composite under uniaxial tensile loading. Shorter mean-free distance between 211 particles depresses the subgrain thickness, the twin complex size, and twin spacing. The level of residual tensile stress in the 123 a-b plane was estimated from detwinning observed around 211 particles.