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

Electron-spin-resonance (ESR) and dielectric spectroscopy techniques have been applied to study the dipole centers connected with Mn2+ and Fe3+ impurity ions substituted for Kf in the incipient ferroelectric KTaO3. It was shown that the reorientations of paramagnetic dipole complexes Fe3+-O-I (O-I is 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 dielectric 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 similar to that in KTaO3:Li was revealed in addition to the aforementioned losses peak. The studies of electric field and temperature dependence of Mn2+ ESR intensities with respect to the local Lorentz field had shown that the dipole 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 directions. The relaxation rate of these dipoles after the polarizing electric field switching off was directly measured by the ESR method. It was described by Arrhenius law with activation energy E-r = 0.104 eV, which is close to the value obtained from dielectric measurements. Possible sources of dielectric 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 present work data and earlier results collected from the literature.