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 τ_o ≈ 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 τ_o ≈ 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.

Key Words:

• Keywords: Incipient ferroelectrics
• Dipole impurities
• Dielectric properties