Crystal field and superposition model analysis for high-spin Fe2+and Fe4+ions in YBa2(Cu1-xFex)3O7- delta

1 October 1991

journal article
Published by IOP Publishing in Superconductor Science and Technology

Vol. 4 (10) , 535-543
https://doi.org/10.1088/0953-2048/4/10/005

Abstract

Crystal field energy levels of Fe²⁺ and Fe⁴⁺ ions at several possible sites in YBa₂(Cu_1-xFe_x)₃O_{7- delta} namely, Cu(1) planar, pyramidal and octahedral sites, as well as Cu(2) sites, have been investigated. The superposition model formulae are developed to relate the crystal field parameters B_k^a with the available crystal structure parameters. The parameters B_k^a are calculated for Fe²⁺ and Fe⁴⁺ ions using the most likely values of the intrinsic parameters determined for crystal structures similar to that of YBa₂Cu₃O₇. The crystal field energy levels and the ground states are then determined for Fe²⁺ and Fe⁴⁺ ions at each site. The superposition model enables the authors to also study the dependence of B_k^a and energy levels on the concentration (x) of Fe ions in YBa₂(Cu_1-xFe_x)₃O_{7- delta}. The ground state for most of the cases considered appears to be an orbital singlet with high spin S=2 and well separated from the excited ⁵D orbital levels due to the strong orthorhombic crystal field. This justifies application, in a subsequent paper, of the spin Hamiltonian analysis to gain further insight into the effects of Fe²⁺ and Fe⁴⁺ ions on the properties of high-T_c 123 superconductors.

Keywords

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