Paramagnetic dipole centers in KTaO3: Electron-spin-resonance and dielectric spectroscopy study

Electron-spin-resonance (ESR) and dielectric spectroscopy techniques have b een applied to study the dipole centers connected with Mn2+ and Fe3+ impuri ty ions substituted for Kf in the incipient ferroelectric KTaO3. It was sho wn that the reorientations of paramagnetic dipole complexes Fe3+-O-I (O-I i s the interstitial oxygen) give rise to dielectric losses near T similar or equal to 185 K at the frequency 1 kHz. Their activation energy E-r = 0.34 eV was obtained both from dielectric and ESR measurements. The peak of diel ectric losses at T similar or equal to 55 K was observed in KTaO3 doped by low concentrations of Mn2+(n approximate to 0.01 at. %). At n greater than or similar to 0.3 at. % a pronounced peak of dielectric susceptibility simi lar to that in KTaO3:Li was revealed in addition to the aforementioned loss es peak. The studies of electric field and temperature dependence of Mn2+ E SR intensities with respect to the local Lorentz field had shown that the d ipole moment 1.4 e Angstrom can be associated with Mn2+ ion. The origin of this dipole moment was shown to be off-center displacement Delta similar or equal to 0.9 Angstrom of Mn2+ from the K+ site in one of six [001]-type di rections. The relaxation rate of these dipoles after the polarizing electri c field switching off was directly measured by the ESR method. It was descr ibed by Arrhenius law with activation energy E-r = 0.104 eV, which is close to the value obtained from dielectric measurements. Possible sources of di electric losses in nominally pure KTaO3 single crystals in the vicinity of T approximate to 40 K are analyzed and discussed on the basis of both prese nt work data and earlier results collected from the literature.