Lanthanum-substituted Y-Ba-Cu-O superconductors synthesized at elevated oxygen pressures

Abstract

Lanthanum substitution in the Y‐Ba‐Cu‐O system at elevated P(O₂) results in superconducting compositions which throw interesting light on the effects of nonisovalent substitution in a Y‐Ba‐Cu‐O system. Like Ca substitution, La substitution also shifts the phase formation boundary between 123, 247, and 124 phases to higher P(O₂), and stabilizes a tetragonal 123 structure at moderately elevated P(O₂). However, in contrast with Ca substitution, T_c decreases continuously and rapidly with increasing La content. This can be only partly explained by a decrease of the hole concentration.