Abstract
High Tc superconducting oxides discovered so far are classified into several systems, that is, 40 K class (La1-xMx) 2CuO4-δ (M : Sr, Ba, Ca), 90K class Ba2LnCu3O7-δ (Ln : rare earth elements excepting Sc, Ce, Pr and Tb), 110K class Bi-Sr-Ca-Cu-O, and 130K class Tl-Ba-Ca-Cu-O systems. These oxides have the perovskite related crystal structures with copper ions on B sites. Mutual relations among these structures are briefly reviewed. The 3d electron holes responsible for the electrical conduction are considered to be Cu3+ from the chemical picture. Therefore the oxygen nonstoichiometry and average copper valence were determined. The relation between critical temperature and average copper valence are shown. The superconducting oxides exhibit normal conductivities of 102 to 103 Ω-1 cm-1 and the temperature coefficienty of nearly zero. This fact would provide a useful guiding principle for finding new superconductors.
