Theoretical investigations of the local structure for the trigonal Co2+ center in MgTiO3 crystal

The local structure of the trigonal Co2+ center in MgTiO3 is theoretically investigated by using the perturbation formulas of the spin Hamiltonian parameters for a 3d7 ion in trigonal symmetry based on the cluster approach. From the studies, it can be found that the impurity Co2+ ion substitutes for Mg2+ rather than Ti4+ ion, and that the Co2+ takes an outward displacement (&ap;0.02 A˚) away from the center of the oxygen octahedron along the <f>C3</f> axis in MgTiO3. The theoretical spin Hamiltonian parameters calculated from the above displacement show good agreement with the observed values. The validity of the results is discussed based on the impurity displacement model for corundum-type structures. [Copyright &y& Elsevier]