MICROSTRUCTURES AT THE INTERFACE BETWEEN AN A-AXIS ORIENTED YBA2CU3O7-X FILM AND A NDGAO3 (110) SUBSTRATE

The interface between an a-axis oriented YBa2Cu3O7-x film and a NdGaO3 (110) substrate has been investigated by cross-section transmission electron microscopy (TEM). The orientational relationship between the a-axis oriented film and substrate is YBa2Cu3O7-x [001] parallel-to NdGaO3 [001]. This preferentially c-axis aligned direction of the YBa2Cu3O7-x film would be caused by a very small lattice mismatch (0.1%) between the b(= a) lattice constant of YBa2Cu3O7-x and a2 + b2)1/2/2 of the pseudo-cubic sub-lattices in NdGaO3 at a substrate temperature of 750-degrees-C. Two kinds of imperfections have been observed in the crystal lattice of YBa2Cu3O7-x near the interface; one is the deviation of YBa2Cu3O7-x [301] from NdGaO3 [111]. The other type is pair dislocations with a positive and negative Burgers vectors in the YBa2Cu3O7-x (103BAR) planes. These two kinds of defects at the interface would act to reduce the tensile stress within a distance of about 1.1 nm from the substrate interface.