DISLOCATIONS, STRAIN, AND DEFECTS IN HETEROEPITAXIAL YBA2CU3O7-X SRTIO3 MULTILAYERS/

The microstructure of two heteroepitaxial YBa2Cu3O7-x/SrTiO3 (YBCO/STO ) multilayers on (110)(rhombohedral) LaAlO3 substrates has been charac terised using high resolution transmission electron microscopy (HREM). The samples differed in the YBCO layer thicknesses, while the STO lay er thicknesses were constant. The YBCO/STO interfaces were smooth and sharp. The individual layer thicknesses were relatively uniform, but t he STO layers were occasionally discontinuous, indicating a three-dime nsional growth mode. The STO (001) planes were tilted a small angle, w hen they followed irregularities in the YBCO layer surfaces. This did not affect the growth of the subsequent YBCO layers. Energy dispersive X-ray analysis revealed a Sr/Ti-ratio between 0.65-0.70 for the STO l ayers. The lattice mismatch between the YBCO and the STO resulted in s trained layers for both samples. Y2O3 precipitates nucleated both on Y BCO and STO. STO was not observed to nucleate on the Y2O3, which creat ed pinholes and destroyed the periodicity of the subsequent layers. (C ) 1998 Elsevier Science B.V. All rights reserved.