ROLE OF CHAIN OXYGEN DISORDER IN CHARGE-TRANSFER IN YBA2CU3O7-DELTA SUPERCONDUCTORS

We present the results of our electronic structure calculations which show that the local coordination and geometry around the chain site Cu atom play a crucial role in the charge transfer interplay between the CuO2 planes and the CuO chains. We find that two-fold, three-fold, and four-fold non-square planar coordinations of the chain site Cu atom are not favourable configurations for electron transfer from the CuO2 planes our calculations show that in YBa2Cu3O6.5 the CuO2 planes remain insulating in the tetragonal structure while approximately 0.16 hole/CuO2 are created in the orthorhombic structure with alternate chains fully intact, and the adjacent ones empty.