A study of electrical characteristics of crystals of homogeneously doped LiNbO$_{3}$:Zn,Mg in the temperature range of 450–900 K

In a series of initially polydomain crystals of LiNbO$_{3}$:Zn,Mg obtained by the homogeneous doping of the crystals in the concentration ranges of around 1 $\pm$ 0.02 mol.% MgO and 3.0 – 4.6 mol.% ZnO, abrupt increases in temperature dependences of electrical conductivity $\sigma(T)$ and dielectric constant $\varepsilon(T)$ with the manifestation of low-frequency dielectric dispersion are observed near $T^*\approx$ 800 K. At $T>T^*$, these crystals exhibit the activation enthalpy ($H_a\approx$ 1.76 – 2.07 eV) and transport enthalpy ($H_m\approx$ 1.55 – 2.01 eV) values that are unusually high for cationic conductors, while both values at $T<T^*$ are typical of conductivity caused by Li$^*$ cations in LiNbO$_{3}$ crystals ($H_a \approx$ 1.2 – 1.4 eV and $H_m \approx$ 1.1 – 1.28 eV). Anomalous increases in the $H_a$ and $H_m$ values for crystals with the LiNbO$_{3}$ structure are apparently associated with the formation of associated vacancies (divacancies) with a finite binding energy and a pair-correlated hop of Li$^*$ ions in the LiNbO$_{3}$ : Zn,Mg crystals in the high-temperature region with increased conductivity $(T>T^*)$.