p(x) and Tc(x) characteristics in the Y 1−b (Ca) b Ba 2 Cu 3 O 6+x cuprate family

A model has been proposed to calculate the p(x) and Tc(x) dependences in the Y 1−b(Ca)bBa2Cu3O6+x high-Tc cuprate family and applied to b=0, b=0.1, and b=0.2 cases, for which experimental data exist in the literature. The results obtained imply that the Ca efficiency to provide holes is independent of the basal plane oxygen concentration, which is consistent with a view that electrons from CuO2 layers would go primarily to Ca since it is twice closer than oxygen (in addition, the chain oxygen is screened by a layer made up of Ba and O(4) ions). It is shown that, in fully oxygenized compounds (x=1) the average efficiency, χ, of a chain oxygen to attract an electron from the two nearby layers is reduced by the Ca insertion, though not because the charge transfer mechanism is in itself weakened by Ca, but because a part of electrons that are otherwise available in CuO2 layers has already been removed by the substitution of Y 3+ with Ca2+. It has been found that the b-dependence of the average oxygen doping efficiency can be fairly accurately described by the following relation: χ(b)=0.39×(1−0.78b). The calculated p(x) and Tc(x) dependences are in very good agreement with the available experimental data.