THE MICROSTRUCTURE OF INTERFACES IN MELT-TEXTURED YBA2CU3O7-X - MECHANISMS OF FORMATION

Microstructures of textured YBa2Cu3O7-x ceramics were examined by tran smission electron microscopy. The samples were synthesized under a res idual thermal gradient by using modified melt textured growth on a Y o xide substrate. Defects running parallel to stacking (ab) planes are i n fact growth defects associated with 211 trapped particles. Microanal ysis of such areas proves the presence of solidified liquid in these d efects. The growth is cellular or dendritic and the texture has many c haracteristics typical of a single crystal. Interfaces formed between 211 and 123 were studied and analysed with reference to the crystalliz ation mechanism. Two types of interface were evidenced: (A) those for which the matrix is deformed and (B) those for which structural (and c hemical) modifications of the inclusions are the main characteristics. The interfaces belonging to group A may be classified according to th e types of defect they create in the 123 matrix. Most coherent interfa ces (interface planes parallel to (010)(123), observed when {110}(123) are parallel to {001}(211)) induce very few defects in the matrix; in terfaces with ordinary coincidences give rise to strongly disordered a reas. Interfaces with no planes in coincidence with the matrix are cha racterized by microprecipitates, which may be viewed as an alternative way for stress relaxation. Type B interfaces are found for small 211 particles; these induce more strain in the matrix than larger ones, an d their composition and structure are also more defective.