Formation mechanism of Y₂BaCuO₅ pattern in growing YBa₂Cu₃O_xgrains during melt-infiltration process

When a melt of BaO and CuO mixture was infiltrated into sintered Y₂BaCuO₅(211) compact to form YBa₂Cu₃O_x(123) superconductor, butterfly-like plane patterns of 211-free regions were observed to form within growing 123 grains. In a 123 grain, the 211-free region was found to be a pair of vertex-shared pyramids and 211 entrapped region to be the rest of the bulk of the grain. An observation of patterns and cracks formed within 123 grains revealed the base of the pyramids to be (001) plane. The difference in entrapment, which depends on crystallographic planes and results in the formation of the pattern, was explained by the dihedral angles between 123 and 211. The dihedral angle between a - (or b-) plane and 211, which is believed to be greater than zero degree, might cause the entrapment of 211 particles in a [100] (or [010]) direction. In contrast, the dihedral angle of most probably zero degree between c-plane and 211 inhibited the entrapment. The observed shape of 211 particles in front of a-(or b-) and c-planes supports the above explanation of 211 entrapment to form the butterfly-like patterns. was explained by the dihedral angles between 123 and 211. The dihedral angle between a- (or b-) plane and 211, which is believed to be greater than zero degree, might cause the entrapment of 211 particles in a [100] (or [010[) direction. In contrast, the dihedral angle of most probably zero degree between c-plane and 211 inhibited the entrapment. The observed shape of 211 particles in front of a-(or b-) and c-planes supports the above explanation of 211 entrapment to form the butterfly-like patterns.