Dependence of <i>T</i> <i>c</i> on hole concentration in the superconductors Bi4Sr3Ca3−<i>x</i>Y<i>x</i>Cu4O16+δ

Abstract

Substitution of Y for Ca in the high Tc superconductor system Bi4Sr3Ca3−xYxCu4O16+δ (0≤x≤1.5) is accompanied by an increase in oxygen concentration δ≊0.34+0.3x that is insufficient to compensate for the increase in counter-cation valence. Nevertheless, Tc≊86 K remains nearly constant in the interval 0≤x≤0.5; it drops smoothly to zero in the interval 0.5&amp;lt;x≤1.15. Correlation of the compositional limit x=0.5 of the Tc plateau with the onset of trapping of holes could indicate that any oxygen atom in excess of O16.5 occupies a different crystallographic position where it traps two holes either as Bi5+ or as (O2)2−.