The effect of high-temperature annealing, in O, Ar and H2O vapour, upon the electron spin resonance spectra of Fe3+ in various local environments was studied. Analysis of experimental data suggested a model, for the rhombic Fe3+ centre, in which Fe3+ near to two O vacancies was substituted for Ta5+: (Fe3+-2VO). Calculation of the crystal field parameters, within the framework of the Newman linear-superposition model, showed that Fe3+ was shifted by 0.025nm from the Ta5+ site, in the [011] direction, inside the O tetrahedron. It was shown that these rhombic Fe3+ centres were static dipoles at 4.2 to 450K, and could not be the source of dielectric losses at 40K.

Local-Structure Model of Rhombic-Symmetry Fe3+ Centre in KTaO3. V.V.Laguta, M.I.Zaritskii, M.D.Glinchuk, I.P.Bykov, A.M.Slipenyuk, J.Rosa, L.Jastrabík: Solid State Communications, 1999, 110[3], 173-8