Vacancy-interstitial annihilation in titanomagnetite by thermal annealing

This paper is concerned with the annealing kinetics of point defects giving rise - in the presence of Ti4+-induced internal stresses - to pronounced, thermally activated magnetic after-effects (MAEs) near 450, 200 and 65 K in single-crystalline titanomagnetites Fe3-x-¿Ti xO4 of composition 0.1<x <0.3 and ¿ <0.005. These relaxation processes have been associated with reorientations of anisotropic point defect configurations of Ti4+-bound octahedral (B-site) vacancies (450 K), Fe2+ interstitials (200 K) and a specific mode of stress-reducing electron hopping (65 K). In order to check the developed model conceptions, crystals have been systematically annealed and the induced variations of the MAE spectra carefully analysed with respect to the underlying defect kinetics. As an important result, the common recovery of the 450 K and 200 K MAEs, in one stage near T > 1000 K, yielded coincident kinetics of reaction order ¿ = 2 and recombination enthalpy Q = 2.45 ± 0.05 eV -as being compatible with bimolecular defect (vacancy) - anti-defect (interstitial) recombination. The delayed recovery of the 65 K peak (at T = 1100 K) points to a stress-sensitive relaxation mechanism, being deactivated only with the final annihilation of stress-producing anisotropic defects. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.