Cu- and Fe- Doping in Properties of Ktao3 and Ktao3 : Li Crystals

To deepen the understanding of the Cu and Fe doping effect in dielectric properties of KTaO3:Li crystals, detail studies of the epsilon' (T,f) and tan [delta(T,f)] (9-300 K, 100 Hz-1 MHz) behavior with a series of nominally pure KTaO3, Cu- and Fe-doped KTaO3 and KTaO3:Li (0.1% +3% mol. in the hatch) crystals were performed, Below 70 K, all pure, Cu- and Fe-doped KTaO3 reveal a universal low-temperature dielectric relaxation seen well in T,f behavior of losses obeying the Arrhenius law with activation energy Delta = 79.3 - 86.2 meV and tau(0) approximate to 6.5 x 10(-14) s. Several F containing KTaO3 specimens displayed an additional low-temperature Arrhenius Debye-type dielectric relaxation with Delta = 74.1 eV and tau(0) = 2 x 10(-14) s. While doping by Fe and especially Cu has insignificant effect on KTaO3 properties, in KTaO3:Li it strongly increases low temperature relaxations and dipole ordering effects. This result is consistent with a model of coupled relaxations involving the off center Li+ and another relaxation dipole defect. This "other dipole defect" can be associated with double-well Cu2+(Ta5+) and Cu+(K+) off centers. Contaminating by Nb impurities dramatically modifies KTaO3:Li properties.