PF-HYBRIDIZATION AND THE CRYSTAL FIELDS IN RBA2CU3O7-DELTA

Mechanisms are considered, which form the crystal field (CF) acting on rare earth ions (REI) in the high-T(c) superconductors RBa2Cu3O7-delta. The electrostatic component of the CF is calculated using the point-charge model. A significant contribution to the CF is brought in by pf-hybridization and is taken into account on the basis of a two-centre approximation using Slater-Koster parameters. A new parameterization of the hybridization contribution to CF is proposed, which is based on utilizing two parameters - the energies E(sigma) and E(pi) of the sigma- and pi-bonds in the pair R3+-O2-. Proceeding from the analysis of the experimental data, it is shown that for all compounds studied thus far (R = Nd, Dy, Ho, Er, Tm) a universal relation holds between these two parameters, E(sigma) almost-equal-to 2.9E(pi), which enables to reduce the number of disposable parameters of the theory.