Temperature-dependence thermoelectric power studies of mixed Ni-Cu nano ferrites

Synthesized Ni-Cu nano ferrites with the compositional formula Ni1−xCuxFe2O4 (x = 0.0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0) were prepared by the citrate-gel auto combustion technique. The prepared samples were characterized using X-ray difractrograms (XRD), Transmission electron microscope (TEM) and Fourier transforms infrared (FTIR). The X-ray difractrograms (XRD) clearly exhibited the existence of single phase cubic spinel structure and the crystallite size was found in the range of 36-58 nm. TEM micrographs indicated the nanostructure nature with platelet shape. FTIR absorption spectra revealed the presence of two significant absorption bands ν1 and ν2 around 580 cm−1 and 410 cm−1 characteristic of spinel ferrite. This confirms the formation of single phase spinel structure with two sub-lattices tetrahedral (A) site and octahedral (B) site. The thermoelectric properties were carried out by the differential method from room temperature to well beyond the transition temperature. The seebeck coefficient is negative for all the compositions showing that these ferrites behave as n-type semiconductors. The transition temperature determined from thermoelectric power studies, it was found that the transition temperature decreases with increase of Cu concentration. The values of the charge carrier concentration and charge carrier mobility have been computed from the observed values of the seebeck coefficient. The temperature variation of the seebeck coefficient and carrier concentration is also discussed. On the basis of these results an explanation for the conduction mechanism in Ni-Cu nano ferrites is suggested.