Effect of lanio₃ on the impedance and dielectric properties of CoFe₂O₄: A high temperature study

In this article, we report the impedance and dielectric properties of the nanocomposites comprising of CoFe₂O₄ (CFO) and LaNiO₃ (LNO) with varying LNO content (0, 5, 10 and 15%) in the temperature range from 35 °C-400 °C. The impedance and modulus spectroscopy show the non-Debye type dielectric relaxation behaviour of the grain and grain boundary separately in pure CFO with an additional relaxation in the composite with 15% LNO, arising from the electrode polarization. Mostly the grain boundary of the composites is affected by the presence of LNO as its activation energy in the composite with 15% LNO is reduced by ∼0.2 eV compared to pure CFO, whereas that of the grain remains similar. The dielectric constant increases consistently with increasing LNO content in the composites owing to the Maxwell-Wagner-Sillar type polarization effect between the interfaces of LNO and CFO. The dielectric constant manifests a negative value in both pure CFO and the composite with 15% LNO at all temperatures in the frequency of hundreds of MHz which is explained by the interband transition. The ac conductivity of pure CFO reveals short range and orientational hopping inside the grains and across the grain boundary, respectively. However, in the composite with 15% LNO, the reduced activation energy assists the charge carriers for short range hopping across the grain boundary while the conductivity inside the grain remains unaffected.