Single-Walled Carbon Nanotube-Controlled Meyer–Neldel Rules in Vanadium Oxide Films for Applications as Thermistor Materials in Sensors and Detectors

Owing to their excellent electrical properties, vanadium oxide (VOx) films are applied widely as thermistor materials in gas sensors and infrared detectors. The Meyer–Neldel rule (MNR) which was first discovered in 1937 has been widely observed in the properties of electrical conductivity, mobility, diffusion, and desorption. Results in this work reveal that the electrical conductivity of VOx films prepared by organic sol–gel and annealed at 265–355 °C obeys normal MNR behavior with a positive Meyer–Neldel activation energy (EMN) of +16 meV. After incorporation of VOx with −COOH-functionalized single-walled carbon nanotubes (SWCNTs), normal MNR with a positive EMN of +13 meV is similarly measured at low annealing temperatures (≤310 °C). But interestingly, a different, inverse MNR with a negative EMN of −43 meV is observed at high temperatures (≥310 °C). This work suggests a new route to chemically convert the macroscopic physical MNR behavior of VOx by SWCNTs. These results will be helpful not only for gaining insights into the origins of and modifying the MNR behaviors but also for rationally controlling the electrical properties of the VOx and VOx–SWCNT films for sensor or detector applications.