The authors show, using a proposed oxygen-defect structure for YBa2Cu3O7-x and a tight-binding model based on density-functional calculations, that the distribution of holes between planes and (fragmented) chains causes jumps and plateaus for the hole counts in the planes as a function of the nonstoichiometry, x. These features can be correlated with the occurrence of the antiferromagnetic as well as the 60 and 90 K superconducting phases. Their findings are supportive of the view that the hole count is the controlling parameter for the superconductivity.
 

Physical Review Letters, 60 2685-8, 1988.