High-permittivity core/shell stuctured NiO-based ceramics and their dielectric response mechanism

High-permittivity dielectric core/shell structured NiO-based ceramics (LSNO) have been successfully prepared. All the LSNO ceramic samples sintered exhibit high dielectric properties, and the dielectric constant reaches about $1.2\ifmmode\times\else\texttimes\fi{}{10}^{4}$ for the LSNO-1 sample. The concentration of Si has a remarkable effect on the dielectric properties of the LSNO ceramics due to the various activation energies corresponding to the dielectric relaxation processes. The experimental results indicate that the polarization relaxation has a close relation with the conductivity in grain interior because the activation energy values, ${E}_{g}$ fitted by the reverse temperature dependence of the relaxation time and ${E}_{a}$ fitted by the reverse temperature dependence of the dc conductivity, are almost same. The origin of the high permittivity observed in these LSNO ceramics is attributed to the Maxwell-Wagner polarization mechanism and thermally activated mechanism. The calculated dielectric constants by the boundary layer model are in good agreement with the experimental results.