Electrical Conductivity and Dielectric Permittivity of Directly Doped LiNbO3:Zn,Mg Crystals in the Temperature Range 450–900 K

Abstract

The electrical conductivity σ of a series of multidomain LiNbO3:Zn,Mg crystals prepared via direct doping in the composition ranges ~1 ± 0.02 mol % MgO and ~2.8–4.6 mol % ZnO has been shown to undergo a sharp increase at T* ≈ 800 K, accompanied by anomalies in temperature dependences of their dielectric permittivity, e(T). The largest increase in their static bulk conductivity near T* has been observed in a narrow composition range (≈1 ± 0.02 mol % MgО and ≈3.9–4.3 mol % ZnO). Above T*, the LiNbO3:Zn,Mg crystals have an activation enthalpy for ionic conduction (Ha ≈ 1.76–2.15 eV) and enthalpy of transport (Hm ≈ 1.66–2.06 eV) unusually high for cation conductors, whereas below T* both quantities are characteristic of Li+ ion conduction in LiNbO3 crystals (На ≈ 1.15–1.35 eV and Нm ≈ 1.0–1.1 eV). The anomalous increase in Ha and Hm is caused by the formation of associated vacancies (divacancies) and correlated pair hopping of Li+ ions above T*.