Effects of DC bias on non-ohmic sample-electrode contact and grain boundary responses in giant-permittivity La1.7Sr0.3Ni1-xMgxO4 ceramics

The effects of DC bias on the giant dielectric properties and electrical responses of non-ohmic sample-electrode contact and grain boundaries of La1.7Sr0.3Ni1-xMgxO4 (x = 0-0.5) ceramics were studied. La1.7Sr0.3Ni1-xMgxO4 ceramics were prepared using a chemical combustion method with urea as a fuel. A pure phase and dense ceramic microstructure were achieved. Using impedance spectroscopy analysis under a DC bias, the giant dielectric properties of an un-doped La1.7Sr0.3NiO4 ceramic were found to be due to a combination of the small polaronic hopping mechanism and non-ohmic sample-electrode contact effect. This was confirmed by a linear Mott-Schottky plot of 1/C-2 vs. DC bias voltage. Doping La1.7Sr0.3NiO4 ceramics with Mg2+ ions caused an increase in the grain boundary resistance, leading to a decrease in the loss tangent and degradation of the electrode effect. The giant dielectric response in La1.7Sr0.3Ni1-xMgxO4 ceramics (x = 0.3-0.5) was primarily attributed to the insulating grain boundary response (i.e., Maxwell-Wagner polarization) coupled with small polaronic hopping of charge carriers.