Studies of the spin Hamiltonian parameters and the local structure for the trigonal Cr3+ centers I, III and IV in CsMgCl3

The spin Hamiltonian (SH) parameters (zero-field splitting D, anisotropic g factors gparallel and gperpendicular) and the local structure of the trigonal Cr3+ centers I, III and IV in CsMgCl3 are studied using the perturbation formulae for the SH parameters for a 3d3 ion in trigonal symmetry based on the cluster approach. In these formulae, not only the contributions from the conventional crystal-field (CF) mechanism, but also those from the charge-transfer (CT) mechanism are taken into account. According to the studies, the metal-ligand bond angle related to the C3-axis is found to increase from β H (∼51.710) in the host to β (∼54.480) in the impurity center I (in the absence of local charge compensation). As for center III (or IV), the three Cl- ions closest to the compensator VMg (or Li+) are expected to displace away from the compensator by an amount ΔXIII ∼ 0.009 nm (ΔXIV ∼ 0.003 nm) due to the electrostatic repulsion. The local structure of the trigonal centers and the contributions from the CT mechanism are discussed