EPR paramaters and defect structure of the trigonal Ti2+ center in ZnS

The axial Ti2+ center in a nearly wholly cubic ZnS crystal is assigned to the Ti2+ ion on the hexagonal site of wurtzite structure caused by stacking faults. On the ground of the assignment, the EPR parameters (zero-field splitting D, g factor g( parallel) and g-anisotropy Deltag=g( parallel)-g( perpendicular)) of the axial Ti2+ center are calculated from the high-order perturbation formulas based on the cluster approach for the EPR parameters of 3d2 ion in trigonal symmetry. From the calculations, the local atom-position parameter u(loc) (which is different from the corresponding parameter u in the host wurtzite structure) and hence the defect structure of the Ti2+ center are estimated. The results (the calculated EPR parameters and the defect structure) are discussed.