Influence of V2O5 ion addition on the conductivity and grain growth of Ni–Zn–Cu ferrites

Polycrystalline nickel–zinc–copper ferrites with chemical formula Ni0.6+xZn0.2Cu0.2VxFe2−2xO4,(0.0 ⩽ x ⩽ 0.25) were prepared by the ceramic route. The X-ray diffraction (XRD) analysis of the samples results confirms single-phase spinel structure. Scanning electron microscopy (SEM) of the prepared ferrites reveal that vanadium addition resulted in a rapid grain growth with large pores trapped inside the grains as the vanadium concentration increases. The ac conductivity σac has been studied as a function of frequency and temperature over the temperature range (300–600 K). The results obtained for these materials reveal a semiconductor – to semimetal transition as V5+ content increases. All studies composition exhibit a transition with change in the slope of conductivity. The obtained temperature Tc is found to be decrease with the increasing vanadium content. The hopping of electrons between Fe3+ and Fe2+ as well as the hole hopping between Ni3+ and Ni2+ are found to responsible for the conduction mechanism. The relation of the universal exponent s with temperature gives evidence for the presence of the correlation barrier hopping (CHB) mechanism in these compounds. The impedance technique has been used to study effect of grain and grain boundary on the electrical properties. The analysis data show only one semi-circle for all samples except for sample with x = 0.05. The results suggested that the conduction mechanism takes place predominantly through the grain in the studied samples.