Dielectric dispersion of the dipolar glass K_0.989Li_0.011TaO₃

Abstract

Dielectric dispersion spectra measured on K_0.989Li_0.011TaO₃ at frequencies 10⁻³ ≤ f ≤ 10⁷ Hz and temperatures 5 ≤ T ≤ 100 K are analyzed in terms of Lacroix-Béné type distributions of relaxation times, G(τ) α (τ - τ)^−β τ _σ is related to the local hopping diffusion of isolated off-center Li⁺ dipoles. It varies as exp(δE/k_BT) with δE/k_B = 910 K at T > 40 K and crosses over into the quantum tunneling limit, τ_min ∼ 10² s as T → 0. The exponent β decreases with decreasing T. β ∼ 0.05 as T → 30 K, in accordance with the observed asymmetric low-frequency broadening of ε″ vs log f. Upon approaching the static freezing temperature, T_g = 33.7 K, power law divergence of τ_max with an exponent zv = 15.1 is observed.