Structural and property evolution during VO2(B) to VO2(M) transition

A two-step synthesis was developed to produce thermochromic VO2(M) nanofibers by vacuum annealing hydrothermally derived VO2(B). It is found that the VO2(B) → VO2(M) transition at 500 °C appears to proceed via a topotactic pathway, allowing the fibrous morphology to be well preserved at nanoscale. The resulting monoclinic VO2(M) nanofibers have diameters of about 20–200 nm and lengths of several micrometers. The VO2(M) nanofibers show three characteristic infrared absorptions at about 1012, 892, and 596 cm−1, providing a clear spectral signature for probing the VO2(M) materials. Differential scanning calorimetry (DSC) reveals a metal–insulator (MI) transition with peaks at about 68.5 °C (heating) and 58.5 °C (cooling), giving a hysteresis of 10 °C. The sharp and well-defined DSC peaks indicate improved homogeneity and stoichiometry in the synthesized VO2(M) materials. The distinct electronic properties exhibited by the VO2(M) nanofibers across the MI transition indicate their potential for infrared-modulating applications.