Giant dielectric response and polaronic hopping in charge-ordered ceramics

The structure and dielectric properties of charge-ordered Nd1.75Sr0.25NiO4 ceramics are presented. The giant dielectric constant about 30 000 is observed in the present ceramics even the frequency is up to 5 MHz. There are three dielectric relaxations at the curve of temperature dependence of dielectric constant in the considered temperature range. Based on the comparison of activation energies of dielectric relaxation and electrical conductivity, the giant dielectric response should be attributed to the bulk factor, that is, thermally activated small polaronic hopping in the present ceramics, while the dielectric relaxation around room temperature should cause from the effect of grain boundaries.