The charge state of Mn and defect dynamics in manganese doped KTaxNb1−xO3

Abstract

The EPR spectra of Mn impurities in KTa1−xNbxO3 crystals (X≂0.03) is studied in the 110–560 K temperature range. Intensity measurements do not support a change in the Mn charge state in the 100–140 K temperature range. The room temperature g factor and hyperfine constant values, g=2.000±0.001 and A=(84.9±0.02)×10−4 cm−1 are very similar to those of Mn2+ in KTaO3 at low temperatures. Thermally induced low-temperature change in the Mn charge state is therefore unlikely. The motional narrowing phenomenon observed at high temperatures (300 K<T<600 K) is very probably due to fast hopping of Mn2+ ions (which sit off-center on K+ sites) between three magnetic inequivalent sites. This is strongly supported by a relaxation matrix analysis of the narrowing which shows that the hopping rate can be characterized by an Arrhenius equation with a low activation energy E=(0.065±0.01) eV which is very similar to the corresponding value in Li:KTaO3, and a preexponent factor 1/τ0=4.5×1012 s−1.