Phase evolution and infrared transmittance in monophasic VO2 synthesized by a rapid non-equilibrium process

Abstract

VO2 displays a semiconducting to metallic (SMT) transition accessible near room temperature. This makes it one of the most sought after materials for electrical and optical switching. But this can be utilized only when the synthesis process yields phase pure VO2 without other oxides of vanadium. Across the SMT, VO2 exhibits difference crystal structures with a rich phase behavior of insulating monoclinic M1, M2 and T phases. The objective of this study is to synthesize phase pure VO2 and to investigate its structural evolution and infrared switching during the transition. In this work, a rapid non-equilibrium process namely Solution Combustion Synthesis (SCS) was employed. The structural phase transition (SPT) of VO2 nanostructures synthesized by SCS was investigated by in-situ temperature controlled XRD across the SMT. Gaussian curve fittings for measured XRD patterns revealed that competing phases of M1 and R significantly contribute to the observed pattern at every increase in temperature. The powders were further characterized by FTIR, DSC and DC electrical conductivity. These studies show that a sharp SMT was observed at 68–70 °C. Infrared transmittance experiments pinpointed the transition. Carrier density and mobility of VO2 were calculated. This suggests that this VO2 thus synthesized displays excellent phase transition behavior and can be utilized in optical and electrical switching.