Yl-xPrxBa2Cu307:Charge Redistribution Between Planes and Chains?

A qualitative discussion is given of the electronic structure and properties of the system Y1-xPrxBa2Cu3O7 in which there is a transition from a high-T(c) superconductor to a magnetic insulator. To reconcile the apparently contradicting experimental data, it is suggested that the progressive hole redistribution between CuO2 planes and chains occurs with increasing x so that for large Pr content all the holes are in chains and none remain in planes. In this picture one can naturally explain the main properties of this system; notably, one gets an insulating state for pure PrBa2Cu3O7, the valence of Pr being still Pr3+. Many other properties of Y1-xPrxBa2Cu3O7-delta are naturally explained as well, and several predictions are made.