Effect of an Iron Impurity on the Electrical Conductivity of LiNbO₃ Crystals

The electrical conductivity of a series of LiNbO₃ crystals grown from the charge of the congruent composition with relatively low iron concentration (up to 0.15 wt % Fe₂O₃) has been studied experimentally. It is found that, at temperatures close to 300 K, the main contribution to the electrical conductivity of these crystals is from two types of the centers with close activation energies. The first type of centers are Fe²⁺ ions, which determines the impurity electron conductivity with the activation energy (0.34 ± 0.01) eV. The second type of centers are ${\text{N}}_{\text{Li}}^{\text{4 + }}$ polarons of small radius with the activation energy (0.29 ± 0.02) eV. The polaron conductivity is shown to be dominate for nominally impurity-free and low-doped "as-grown" LiNbO₃ crystals at T = 300 K.