THE EFFECT OF 3dn IMPURITIES IN THE YBa2Cu3O7−δ SUPERCONDUCTOR

The electronic structure of the CuO chain and the CuO 2 plane in the superconductor YBa 2 Cu 3 O 7−δ doped with 3dn transition-metal (TM) atoms are investigated. The calculations were performed through the semiempirical INDO/S technique, where the correlation effects are taken into account by the Configuration Interaction (CI) procedure. We also calculated, for all 3dn impurities, the Hubbard parameters Udd corresponding to a narrow band. The results obtained demonstrate clear chemical trends in the electronic structure of the 3d's, from Ti to Ni, when they substitute Cu(1) and Cu(2) sites; the hybridization decreases when the atomic number Z decreases. Our work provides a picture which is important to understand the change in T c when the host is doped with TM atom.