FORMATION MECHANISM OF Y2BaCuO5 PATTERN IN GROWING YBa2Cu3Ox GRAINS DURING MELT-INFILTRATION PROCESS

When a melt of BaO and CuO mixture was infiltrated into sintered Y2BaCuO5 (211) compact to form YBa2Cu3Ox (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 the 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, is 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 inhibits 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. 18 refs.