Valences of Cu in Y_1-xCa_xBa₂Cu₃O_6+y

The valences of Cu in Y_1-xCa_xBa₂Cu₃O_6+y have been investigated by using complex chemical bond theory. The results for the valences of Cu(1) and Cu(2) in the calculation suggest that the holes introduced by calcium substitution only reside in CuO₂ planes, and there is a competition mechanism for the hole density in CuO₂ planes between Ca doping and oxygen depletion. These conclusions are satisfactorily in agreement with experiments.