Superconductivity and charge transfer compensation by direct doping in the La(1+x)Ca(y)Ba(2-x-y) Cu3O(7+delta) system

Substitution of La and Ca on the Y and Ba sites in the 1-2-3 structure permits an investigation of charge transfer in the solid solution La(1+x)Ca(y)Ba(2-x-y)Cu3O(7+delta) for doping over a wide compositional range. The superconducting, structural, and optical properties of this system are reported. Changes in the charge balance due to La(+3) substituting on the Ba(+2)-site are compensated by increased oxygen content, and the superconducting properties are maintained over a wide range of x and y due to the presence of Ca. We find that the apex O4 frequency does not exhibit significant frequency shifts which is consistent with the hypothesis that the apex O4 vibration is related to the electronic charge state of the Cu-O planes in the 1-2-3 structure.