Electrical Conductivity of LiNbO3 Crystals under Temperature Effect in Vacuum

The temperature dependence of static electrical conductivity σ dc ( T ) of LiNbO 3 single crystal (sp. gr. R 3 c ), oriented along the crystallographic c axis, has been studied using impedance spectroscopy. The impedance was measured under temperature effect in vacuum in a heating–cooling cycle. The σ dc ( T ) dependence with activation energy E a = 1.22 eV, caused by migration of lithium vacancies , was obtained upon heating. Upon cooling, the σ dc ( T ) curve can be divided into three regions with activation energies of 0.66, 0.915, and 0.285 eV. After the measurements in vacuum, color centers containing oxygen vacancies and electrons were formed in the crystal bulk. A thermal effect in vacuum on a LiNbO 3 crystal changes the mechanism of electrical conductivity from ionic to mixed ionic–electronic. At 673 K, the ionic conductivity upon cooling is 3.2 × 10 –6 S/cm, which exceeds the σ dc value upon heating by a factor of about 4. At 500 K, the electronic conductivity upon cooling is 4.3 × 10 –7 S/cm, which exceeds the σ dc value upon heating by a factor of about 515 (extrapolation).