Characterisation of the temperature-dependent M1 to R phase transition in W-doped VO2 nanorod aggregates by Rietveld refinement and theoretical modelling
Understanding the mechanism of the monoclinic-to-rutile (M1-R) phase transition in VO2 is a necessary step in optimizing this material’s properties for a range of functional applications. Here, Rietveld analysis of synchrotron X-ray powder diffraction patterns is performed on thermochromic V1-xWxO2 (0.0 ≤ x ≤ 0.02) nanorod aggregates over the temperature range 100 ≤ T ≤ 400 K to probe the M1-R phase transition that occurs in these materials. Precise measurement of the lattice constants of the M1 and R phases enabled the onset (Ton) and endset (Tend) temperatures to be determined accurately for different dopant levels. First-principles calculations reveal that the observed decrease in both Ton and Tend with increasing W content is a result of Peierls type V-O-V dimers being replaced by linear W-O-V dimers. The results are interpreted in terms of the bandwidth-controlled Mott-IMT model. Our current findings lay the foundation for physically explaining the versatile properties of phase transition materials.