Dielectric dispersion of the dipolar glass K0.989Li0.011TaO3

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Abstract
Dielectric dispersion spectra measured on K0.989Li0.011TaO3 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/kBT) with δE/kB = 910 K at T > 40 K and crosses over into the quantum tunneling limit, τmin ∼ 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, Tg = 33.7 K, power law divergence of τmax with an exponent zv = 15.1 is observed.