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DF: Fachverband Dielektrische Festkörper

DF 11: Small Polarons in LiNbO₃

DF 11.7: Vortrag

Mittwoch, 18. März 2015, 11:40–12:00, EB 133C

Temperature dependence of polaron relaxation in iron-doped congruent lithium niobate: a Monte-Carlo simulation — •Laurent Guilbert and Imed Mhaouech — Laboratoire Matériaux Optiques, Photonique et Systèmes, Université de Lorraine et Supélec, 2, Rue E. Belin 57070 Metz (France)

The three elementary processes involved in the relaxation of bound polarons NbLi⁴⁺ in iron-doped lithium niobate (trapping at Fe³⁺ ions, hopping on Nb antisites and spontaneous conversion to the free polaron state NbNb⁴⁺) are simulated in a Monte-Carlo loop. Simulated decays match more or less the Kohlrausch-William-Watts law, exp[−(t/τ)^b], similarly to experimental decays recorded by light-induced absorption (LIA) and reported in the literature. We focus here on the temperature dependence of the decays. As expected, the Arrhenius plots log(τ) or log(<τ>) (average lifetime) versus 1/T evidence three regimes. Their activation energies reflect, but are however not strictly equal to, the energy barriers of the elementary processes. As far as b is concerned, a low-T limit is found. It corresponds to the trapping regime in which most of the bound polarons are trapped in a single hop. The limit value of b depends mainly on the Fe³⁺ trap concentration and on the orbital parameter c involved in the distance dependence of the trapping time in exp(r/c). The sharp increase of b(T) above 300 K, experimentally evidenced but poorly explained in previous models, now appears as a natural consequence of a trap size effect.