Studies of the EPR g factor for Ni2+ ion in CsMgX3 (X=Cl, Br, I) crystals.

The complete high-order perturbation formula of g factor, including not only the widely used crystal-field (CF) mechanism, but also the neglected change-transfer (CT) mechanism in the CF theory, is established for a 3d8 ion in cubic octahedral site. From the formula, the g-shifts Deltag (=g-gs, where gs approximately 2.0023, the value of free electron) of Ni2+ ion in CsMgX3 (X=Cl, Br, I) crystals are calculated. The results suggest that the g-shift DeltagCT due to the CT mechanism and the DeltagCF due to CF mechanism have the same sign and the importance of DeltagCT follows the order: CsMgI3: Ni2+>CsMgBr3: Ni2+>CsMgCl3: Ni2+. So, in the calculations of g or Deltag of 3dn MXm clusters in crystals, the contributions to g factor from both the CT and CF mechanisms should be taken into account in the case of heavy-element ligand ions, such as Br- and I- ions.