A TEM STUDY OF MICROSTRUCTURES IN A YBCO OXIDE FORMED BY 123 AND CUO INTERGROWTH

Microstructures in intergrown 123 and CuO material prepared by solid state reaction have been examined by transmission electron microscopy (TEM). Samples are of nominal composition Y:Ba:Cu = 1:2:4. As produced, samples are often found to exhibit microstructure with disordered cations which leads to a distortion of the (001) planes in the 123 structure. After annealing (780-degrees-C, 1 atm. O2 for 30 days), it is found that the equiaxial CuO particles can be partially dissolved, forming a structure with intercalations of excess CuO layers in the 123 grains on the (001) plane. This intercalation can be ordered over short distances. In the intergrown 123 and 124 phases, 3-6-11, 4-8-15, 3-6-10 and 5-10-16 structures with c = 38.8, 104.9, 73.9 and 120.6 angstrom, respectively, have been found to exist in this material. These results indicate that the post-annealing process influences the microstructure of the intergrown materials and that new long-period phases can be made in the Y-Ba-Cu-O system.