Crystal Chemistry of Oxide Superconductors - Synthesis and Properties of (Y,La,Ba)₃Cu₃O_y Pseudo-ternary System

Superconductig compounds of pseudo-ternary (Y, La, Ba)₃Cu₃O_ysystem were synthesized and crystallographic parameters and superconducting properties were measured. Compounds of YBa₂__xLa_xCu₃O_yseries were found to be single phase up to x=l and orthorhombic to tetragonal transition at room temperature took place with x=0.5. Tc decreased with increasing x and superconductivity disappeared for x>0.6. These results can be interpreted to be due to the decrease In average valence of copper ions from 2.33 of YBa₂Cu₃O₇with increasing x, which was caused by the substitution of divalent Ba Ions by trivalent La ions. On the other hand complete solid solution was formed for Yj__xLa_xBa₂Cu₃O_yseries, where Tc decreased gradually with increasing x. Considerable increase In Tc was found for the La substituted specimens by annealing around 400°C for 24hrs.