High‐resolution electron microscopy study on crystal structures of high‐T_c superconductors

Recent studies of high‐resolution electron microscopy on the high‐T_c superconductors of Y‐Ba‐Cu‐O and Bi‐Ca‐Sr‐Cu‐O are presented. The observed images of crystals thinner than 3 nm, taken under conditions that approached the Scherzer defocus condition, directly show the arrangements of cations and oxygen‐vacant positions. The results reveal structural characteristics of the atomic scale; this offers important insights into the origin of the high‐T_c superconductivity. The usefulness of high‐resolution electron microscopy for studying complicated crystal structures is demonstrated for the high‐T_c oxides.