Cu− and Fe− doping in properties of KTaO3 and KTaO3:Li crystals

Abstract

To deepen the understanding of the Cu and Fe doping effect in dielectric properties of KTaO3:Li crystals, detail studies of the ε’ (T, f) and tan [δ(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 batch) 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 Δ = 79·3 − 86·2 meV and τo ≈ 6·5 × 10−14 s. Several Fe containing KTaO3 specimens displayed an additional low-temperature Arrhenius Debye-type dielectric relaxation with Δ = 74·1 eV and τo ≈ 2 × 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.