Electrical and dielectric properties of polycrystalline VO2 discriminating between bulk and grain boundary conduction

Electrical and dielectric properties were measured on polycrystalline VO2 samples in the neighborhood of the metal -> insulator transition (MIT) temperature of similar to 340 K, prepared with the ceramic sintering technique. It is shown that in certain temperature ranges in the monoclinic semiconducting M1-phase below the MIT, bulk and grain boundary (GB) effects can be distinguished applying the method of impedance spectroscopy. An enormous literature has accumulated, dealing with electrical properties of VO2 small films and nanowires, with the aim to prepare various kinds of micro-devices for technology. Evidently, investigations to separate bulk from GB effects are largely missing, although many small films and nanowires are polycrystalline. The structure of their GBs doubtless differs from that in macroscopic samples, nevertheless valuable information might be supplied concerning electrical conduction across and along GBs, compared with conduction in the bulk. GB processes in our VO2 samples could be measured between room temperature and the MIT, bulk properties along with GB conduction could only be studied at low temperatures.

Automated summary

Impedance spectroscopy was used to distinguish between bulk and grain boundary effects on polycrystalline VO2 samples near the metal-insulator transition temperature. While there is extensive literature on the electrical properties of VO2 thin films and nanowires, there is a lack of studies separating bulk and grain boundary effects. The structure of grain boundaries in polycrystalline samples is different from that in macroscopic samples, but provides valuable information on electrical conduction. Grain boundary processes in VO2 samples could be measured at room temperature to the transition temperature, while bulk properties and grain boundary conduction could only be studied at low temperatures.