It is important to combine characterization techniques such as electron microscopy with novel materials synthesis in the study of high Tc superconducting phases. Results from electron microscopy studies have been correlated with structure determinations made using x-ray and neutron diffraction (1.2,3.4). Superconducting phases studied to date include YBa2Cu3O7-x, La1.25Ba1.75Cu3O7, Bi2Sr2CuO6, Bi2Sr2CaCu2O8, Tl2Ba2CuO6 Tl2Ba2CaCu2O8, and Tl2Ba2Ca2Cu3O8. A comparison between structures and defect populations suggests that structural defects, which modify the Cu-O arrangement (sheets or chains) intergrowths and grain boundaries, will affect superconductivity. Techniques used in this investigation include HREM, CBED, AEM, SAD and conventional imaging techniques.Samples characterized in this study were prepared in our laboratory, using both conventional and novel synthesis routes. Powder samples in the Tl-Ba-Cu-O system were prepared by heating mixtures of high purity BaO2, Tl2O2 and CuO to 850-900°C in sealed gold tubes for 1-6 hours (3,4). Similar procedures were followed in the Bi2Sr2CaCu2O8 system using Bi2O3, CaCO3, SrO2/Sr(NO3)2 and CuO. heating the mixtures in air at 700-900°C for 12-36 hours (2.4).