Analysis of the microstructure of superconducting YBCO foams by means of AFM and EBSD

YBa₂Cu₃O_y (YBCO) foam samples show an open, porous foam structure, which may have benefits for many applications of high-T_c superconductors. As the basic material of these foams is a pseudo-single crystalline material with the directional growth initiated by a seed crystal similar to standard melt-textured samples, the texture of YBCO is a very important parameter. Therefore, we analysed the local texture and grain orientation of the individual struts forming the foam by means of atomic force microscopy (AFM) and electron backscatter diffraction (EBSD). Due to the processing route starting with Y₂BaCuO₅ (211), a two-phase analysis must be performed, so a high surface quality is necessary to enable an automated EBSD scan. Good quality Kikuchi patterns were obtained from both the YBCO and 211 phases. We found an inhomogeneous distribution of the residual 211 particles, which are mainly randomly oriented and have sizes ranging between 200 nm and 15 µm. In contrast to this, the YBCO matrix shows a dominating orientation with cracks with a typical distance of 1–10 µm. Furthermore, the analysis of strut cross-sections reveals that the entire strut is converted to the YBCO phase.