Electrical, thermoelectrical and magnetic properties of approximately 20-nm Ni-Co-O nanoparticles and investigation of their conduction Phenomena ,

Understanding the properties of semiconductor nanostructures is important for developing their practical
applications in the nanodevices. Although the electrical properties of spinel oxides containing Ni
and Co have been studied extensively over the last decades, there is still a significant disagreement on
their electrical conduction mechanisms and the distribution of the various charge states of Co and Ni in
the octahedral and tetrahedral sites of the spinel crystal lattice. In this study, Co3O4, NiO, and mixed Ni-
Co oxide nanoparticles (NPs) of ~20 nm are synthesized by co-precipitation method. The mechanism of
the electrical conduction in the Co3O4 and Ni-Co oxides NPs is due to the hopping process in the octahedral
site or between the octahedral and tetrahedral sites while in the NiO NPs, the large polarons
conduction mechanism dominates. The thermoelectric power measurements confirm that the Ni-Co
oxides NPs are non-degenerate semiconductors and the diffusion mechanism is the dominant component
of the Seebeck coefficient. In contrast, the Co3O4 NPs show degenerate features with Fermi energy
0.054 eV. The NiO NPs exhibit a transition from non-degenerate to degenerate state. The magnetic
measurements reveal an antiferromagnetic-paramagnetic transition at N
eel transition temperature. The
results are helpful to understanding the fundamental characteristics of the NPs under study.