Finite size effect and influence of temperature on electrical properties of nanocrystalline Ni–Cd ferrites

Abstract

Electrical conductivity and dielectric measurements have been investigated for four different average grain sizes ranging from 3 to 7nm of nanocrystalline Ni0.2Cd0.3Fe2.5−xAlxO4 (0.0⩽x⩽0.5) ferrites. The impedance spectroscopy technique has been used to study the effect of grain and grain boundary on the electrical properties of the Al doped Ni–Cd ferrites. The analysis of data shows only one semi-circle corresponding to the grain boundary volume suggesting that the conduction mechanism takes place predominantly through grain boundary volume in the studied samples. The variation of impedance properties with temperature and composition has been studied in the frequency range of 120Hz–5MHz between the temperatures 300–473K. The hopping of electrons between Fe3+ and Fe2+ as well as hole hopping between Ni3+ and Ni2+ ions at octahedral sites are found to be responsible for conduction mechanism. The dielectric constant and loss tangent (tanδ) are found to decrease with increasing frequency, whereas they increase with increasing temperature. The dielectric constant shows an anomalous behavior at selected frequencies, while the temperature increases, which is expected due to the generation of more electrons and holes as the temperature increases. The behavior has been explained in the light of Rezlescu model.