Metal-semiconductor transition and Seebeck inversion in CoFe2O4 nanoparticles

A Semiconductor to metal transition has been observed in hydrothermally synthesized CoFe2O4 (CFO) nanoparticles. Temperature dependent Seebeck coefficient was measured in order to confirm the type of majority charge carriers and conductivity vs. temperature measurement was performed to get the activation energy. The CFO nanoparticles shows p-type semiconducting behaviour at lower temperature as confirmed by the sign of Seebeck coefficient and at elevated temperatures a sign inversion in Seebeck voltage was observed. The p-type and n-type semiconducting behaviour have been attributed to hopping of holes and electrons between Co3+-Co2+ and Fe2+-Fe3+ respectively dominating at different temperatures.