Crystal field analysis for 3d⁴ and 3d⁶ ions with an orbital singlet ground state at orthorhombic and tetragonal symmetry sites

Authors:

• Czesław Zygmunt Rudowicz,
• Zhou Yi-Yang,
• Yu Wan-Lun

Abstract

The energy level structure of 3d⁴ and 3d⁶ ions in an orthorhombic crystal field in the ⁵D approximation is studied. The first and the second kind of orthorhombic symmetry sites in crystals, which differ in the orientation of the crystal field axes, are considered. Possible energy level schemes with an orbital singlet ground state are established and analysed in detail. General conditions for the orthorhombic crystal field parameters necessary to obtain a given energy level scheme are derived. Results are presented in the form of suitable ground state "phase' diagrams to facilitate the analysis of spectroscopic data. Using the superposition model the formulas relating the crystal field parameters with the crystal structure parameters are derived for 3d⁴ and 3d⁶ions at octahedral sites with the first and second kinds of orthorhombic distortion, as well as for tetrahedral orthorhombically distorted sites. Due to the ascent in symmetry method the results are also applicable to those tetragonal symmetry cases involving real crystal field terms. A literature survey has revealed numerous cases of Fe²⁺ (3d⁶) ions with high-spin S = 2 at the first and second kinds of orthorhombic symmetry sites as well as at tetragonal symmetry sites. Several pertinent cases for 3d⁴ (Cr²⁺, Mn³⁺, Fe⁴⁺) and 3d⁶ (Co³⁺) ions have also been identified. The present crystal field analysis provides grounds for subsequent microscopic spin-Hamiltonian and high frequency EPR studies of 3d⁴ and 3d⁶ ions. © 1992.