Electron-hopping modes in NiMn2 O4+δ materials

Abstract

The resistance versus temperature (R-T) characteristics of NiMn2 O4+δ 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. © 2005 American Institute of Physics.