Grain and grain boundary effects in high-permittivity dielectric NiO-based ceramics

We present a Li and Ti codoped NiO-based polycrystalline ceramic with high-permittivity dielectric properties. Analysis of the ceramic microstructure and composition proves that obvious grain boundaries are formed. The measurements of frequency and temperature dependence of impedance and dielectric permittivity indicate that the grain and grain boundaries have remarkable influence on the dielectric properties due to the various activation energies corresponding to the dielectric relaxation processes. Our results also demonstrate that the activation energy required for relaxation Ea is almost the same to the activation energy of the conductivity in the grain interiors Eg.