Electron-hopping modes in NiMn2O4+δ materials

Abstract

The resistance versus temperature $\left(R–T\right)$ characteristics of ${\mathrm{NiMn}}_2{\mathrm{O}}_{4+\delta }$ thermistors have been analyzed. In the literature, electron transport in manganate spinels is commonly described by a small-polaron model for nearest neighbor hopping, but variable range hopping (VRH) has not been considered so far. In this study differentiated $R–T$ data were analyzed, allowing a clear distinction between different modes of hopping. In pressed pellets and thick screen printed films conduction was well described by a VRH model for a parabolic density of states, which was confirmed by scanning tunneling spectroscopy.