Investigations on the angular distortions around V2+ in CsMgX3 (X=Cl, Br, I)

The local structures for V2+ in CsMgX3 (X=Cl, Br, I) are theoretically investigated from the perturbation formulas of the EPR parameters (zero-field splitting, g factors and the hyperfine structure constants) for a 3d3 ion in trigonal symmetry based on the cluster approach. In these formulas, the contributions from the s-orbitals of the ligands, which were usually neglected in the previous treatments, are considered here. Based on the studies, we find that the local angles β (between the impurity-ligand bonding lengths and the C3 axis) in the V2+ centers are larger than the angles βH in the hosts, leading to the positive angular distortions Δβ(=β-βH). The theoretical EPR parameters (particularly the results for CsMgI3) show improvement compared with those in absence of the ligand s-orbital contributions or the above angular distortions.