Electrical conduction in Ti substituted Ni-Zn ferrites

The d.c. electrical resistivity (rho) and thermoelectric power (alpha) as a function of temperature are made on the system Ni0.5+xZn0.5TixFe2-2xO4 with x = 0, 0.1, 0.2, 0.3 and 0.4 in the temperature range of 300 to 800K. The increase in resistivity with composition is attributed to increase in Ti concentration in the system. The sample with Ti =0.4 show anomalous resistivity behaviour. Conduction phenomenon is due to hopping of polarons. The variation of Seebeck coefficient (alpha) with temperature shows that, the sample with x = 0 show n-type where as remaining sample show p-type at room temperature. The n-p transition takes place for sample with x = 0.2, 0.3 and 0.4 at higher temperature, and this can be related to the presence of Fe2+ and Ni3+ ions respectively. The temperature variation of thermoelectric power suggests that these ferrites are nondegenerate semiconductors.