Thermoelectric power studies of Co–Cr nano ferrites

• CoFe2O4 behaves as n–type semiconductor in the temperature range of 320–800 K.
• All CoCrxFe2-xO4 behave as p-type up to 360K and above 360K as n-type semiconductor
• ‘α’ value increases with increase in Cr content at lower temperature.
• The value of thermoelectric power shows maximum at Curie temperature Tc (K).
• The conduction up to Tc is due to polarons and above Tc due to magnetic transition.

One of the Electrical transport properties, Thermoelectric power of Cr substituted Cobalt Nano structured Ferrite materials with the formula CoCrxFe2−xO4 (0 ⩽ x ⩽ 1), prepared by Sol–gel process were studied. The measurements were carried out from 320 K to well beyond Curie temperature by the differential method. The results showed a negative value for Seebeck coefficient for CoFe2O4 (x = 0), indicating n-type semiconductor behavior over the entire measured temperature range with the electrons as majority of charge carriers. CoCrxFe2−xO4 ferrites (with x = 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) behave as p-type semiconductors up to 360 K with positive Seebeck Coefficient above which they behave as n-type semiconductor. Ferrite with the composition CoCrFe2O4 has shown maximum value of Seebeck coefficient at all temperatures. Compositional and temperature dependence of the Seebeck coefficient in the present ferrite system has been discussed. On the basis of these results a conduction mechanism for Co–Cr nano ferrites system is suggested in different temperature regions. The value of thermoelectric power shows maximum value at Tc (K).