Dielectric relaxation and dielectric response mechanism in (Li, Ti)-doped NiO ceramics

Abstract

Giant dielectric permittivity (Li, Ti)-doped NiO (LTNO) ceramics are prepared by a simplePVA sol–gel method. The dielectric properties are investigated as a function of frequency(102–106 Hz) at different temperatures (233–473 K). The concentration of Li has a remarkable effecton the dielectric properties of the LTNO ceramics. The modified Cole–Cole equation,including the conductivity term, is used to describe the experimental dielectric spectra of ahigh permittivity response with excellent agreement over a wide range of frequencies(103–106 Hz) and temperatures (233–313 K). A frequency dielectric dispersion phenomenon in anLTNO ceramic is also analyzed by impedance spectroscopy. A separation of the grain andgrain boundary properties is achieved using an equivalent circuit model. Thegrain and grain boundary conduction and the dielectric relaxation time of theLi0.05Ti0.02Ni0.93O follows the Arrhenius law associated with estimated activation energies of 0.216,0.369 and 0.391 eV, respectively. Through the analysis by the modified relaxationmodel and impedance spectroscopy, it is strongly believed that the high dielectricpermittivity response of the LTNO is not only contributed by the space chargepolarization (Maxwell–Wagner polarization) mechanism at low frequency regions,but also by the defect-dipole polarization mechanism at high frequency regions.