124 Superconductor stabilized by hole donor (Ca) along with acceptor (La) substitution

Abstract

Substitution of Ca²⁺ in place of Y³⁺ together with equal substitution of La³⁺ for Ba₂₊ in Y-Ba-Cu-O system at elevated P(O₂) extends the stability range of 124 up to a total (Ca+La) concentration of 0.6 atoms per formula unit. The extended stability range of the 124 structure with donor and acceptor co-doping indicates that the relative stability of 124 versus 123 phase is determined to some extent by the hole concentration. The T_c of 124 remains nearly unaffected by even large substitutions of Ca and La so long as they are balanced, so as to give the correct hole concentration; the variation of T_c with separate donor or acceptor doping is caused primarily by the change of hole concentration and Ba does not appear to play a unique role in the high temperature superconductors of the 123/124 family.