Innovative sintering process for fabrication of thermochromic smooth VO2 ceramics

Abstract

In this paper, a pyrolysis method is used to synthesize high quality VO2 powder. Black carbon and V2O5 powder are mixed and annealed at 650 °C or 800 °C under argon flow to initiate a carbo-reduction reaction. The 650 °C VO2 powder presents submicron particle size with an amorphous fraction estimated at 11.5%. With the increase of the annealing temperature up to 800 °C, grains become larger than the micron while the crystallinity goes up to 98.5% (i.e. amorphous fraction drops to 1.5%). This one-step process allows the preparation of quantities up to 10 g of VO2 powder and should be easily transferable to large-scale production. An innovative sintering process is then adopted to produce high quality thermochromic VO2 ceramics from the as-prepared VO2 powder. First, SPS process is used to obtain high-density VO2 pellet. Then, the VO2 pellet is post-annealed in a homemade induction furnace at 1300 °C under a controlled atmosphere to allow grain growth by coalescence and improve pellet surface quality. According to a surface topography analysis, the mean amplitude roughness parameter (Ra) of the obtained VO2 ceramic is found to be 2.93 ± 0.01 nm. A large resistance change by three orders of magnitude along the phase transition is observed, which makes the as-prepared smooth VO2 ceramic a promising candidate for various applications requiring optical and/or electronic switching behavior depending on temperature.