The charge state of Mn and defect dynamics in manganese doped KTa_xNb_{1 − x}O₃

The EPR spectra of Mn impurities in KTa_1−xNb_xO₃ 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 Mn^{2 +} in KTaO₃ at low temperatures. Thermally induced lowâ€�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 Mn^{2 +} ions (which sit offâ€�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/Ï„₀=4.5×10^{1 2} s^−1.