Studies of the spin-Hamiltonian parameters and defect structure for the tetragonalFe5+ centerin SrTiO3 crystals using a two-mechanism model

Abstract

The high order perturbation formulas for spin-Hamiltonian (SH) parameters(g factors and zero-field splitting D) for 3d3 ions in tetragonal symmetry are established using a cluster approach. In these formulas,not only is the contribution to the SH parameters from the crystal-field (CF)mechanism included, but so also is that from the charge-transfer (CT) mechanism(which is neglected in the widely used CF theory). From these formulas, theg shifts (, where ge≈2.0023, the value for the free electron), () and the zero-field splitting D for the tetragonal Fe5+ center in SrTiO3 crystal are calculated. The results (in particular, the positiveg shifts, which cannot be explained on the basis of the CF mechanism) are in goodagreement with the observed values. The calculation results show that (i) the sign ofΔgiCT ( or ) due to the CT mechanism is opposite to that ofΔgiCF due to the CF mechanism, but the sign ofDCT is the sameas that of DCF and(ii) the ratio |QCT/QCF| (which represents the relative importance of the CT mechanism) takes values of about143%, 143% and 114% for , and D, respectively. This suggests that the positiveg shifts are due mainly to the contribution of the CT mechanism; therefore for the high valence state3dn ions in crystals, the contribution to SH parameters from the CTmechanism should be taken into account. The defect structure of theFe5+ centerin SrTiO3 crystal is also obtained from the calculations. The result is consistent with the expectationsbased on charge compensation and electrostatic interaction.