Modulated structure and hopping transport mechanism involving a defect-induced localization–delocalization transition in a Ca–Ce(La)–Nb–W–O system

Abstract

CaCeNbWO8-δ (CCNWO) oxide is a three-dimensional semiconductor with potential applications in electronic devices. It has been reported that the temperature dependence of the resistivity of CCNWO deviates from that predicted by the Arrhenius equation over a wide temperature range. However, its complex hopping transport mechanism has remained unclear due to unknown defect structures. A combination of transmission electron microscopy and the density functional theory showed that CaCeNbWO8-δ and CaCe0.5La0.5NbWO8-δ have a modulated defect structure, and the carriers mainly undergo a Nb4d→W5d transition. At low temperatures, anisotropic defects promote the diversification of transport properties, variable-range hopping, and nearest neighbor hopping. With increasing temperature, isotropic defects promote simplification of the transport property. Compared with CCNWO, CaCe0.5La0.5NbWO8-δ, with a more stable structure, has stronger electron–electron interactions and shifts the localization–delocalization transition point to a higher temperature. The proposed hopping transport mechanism involving a defect-induced localization–delocalization transition allows semiconductor design and device integration schemes, thus impacting a variety of applications.