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 YBaCuO 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 d₂₁₁.V₁₂₃/V₂₁₁ (d₂₁₁ means 211 particle size, V₁₂₃ means 123 volume fraction, V₂₁₁ 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.