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

Abstract

Superconductig compounds of pseudo-ternary (Y, La, Ba)₃Cu₃O_y system were synthesized and crystallographic parameters and superconducting properties were measured. Compounds of YBa₂-_xLa_xCu₃O_y series were found to be single phase up to x=1 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 YBa₂Cu₃O₇ with 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 Y₁-_xLa_xBa₂Cu₃O_y series, 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.