Production of VO2 M1 and M2 nanoparticles and composites and the influence of the substrate on the structural phase transition.

A two-step, high-purity, high-yield synthesis of nanoparticulate vanadium dioxide, which has a greater than 10-fold potential cost reduction is reported. This consists of a short reflux of V2O5 with aspartic acid, followed by calcination at 600 degrees C or above. The particles produced have a mean diameter of approximately 90 nm with phase change characteristics of transition temperature and enthalpy that compare favorably with a commercial standard. In cases where the reduction reaction has progressed too far and a mixture of vanadium(III) and -(IV) is formed, redispersion and aging of the particulate product in water preferentially oxidizes the vanadium(III) component to vanadium(IV), thus allowing a versatile route to achieving a high-purity material. The synthesis was also used to deposit high-purity phases of VO2 onto the surfaces of other particles, and significant differences in the structural phase transition behavior and even the crystal structure were found for deposited samples. The data suggest that substrate properties may affect the characteristics of the structural phase transition, and this has significant implications for measurements on, and applications of, deposited VO2 layers and films.