Impedance spectroscopic studies on congruent LiNbO₃single crystal

Abstract

Electrical impedance measurements on a congruent LiNbO3 single crystal were performed as a function of both temperature and frequency. The measurements were carried out in the directions along the c- and a-axes of the crystal. The temperature and frequency dependence of various dielectric properties have been studied. The result has revealed two remarkable dynamic relaxations: dielectric dipolar relaxation and ionic conductivity relaxation. The dipolar relaxation peaks were found at frequencies around 4 × 106 and 2 × 106 Hz for the c-axis and a-axis, respectively, and they were only slightly temperature dependent. The ionic conductivity relaxation was found at the lower-frequency end but it was temperature dependent. The temperature dependence of the dc electrical conductivity follows the Arrhenius law. It corresponds to the long-range ionic motion of Li+ ions which are thermally activated with activation energy of 0.90 and 0.87 eV along the c- and a-axis directions, respectively. The dc conductivities measured along the c- and a-axes are very close to each other, and the value increases from 1.7 × 10−6 to 1.9 × 10−3 Ω−1 cm−1 as the temperature is raised from 300 to 700 °C. The sample crystal becomes an ionic conductor as the temperature is raised.