Hydrothermal synthesis of VO2(B) and its phase transformation to VO2(M): Investigating metal–insulator transition behavior

Abstract

In this study, VO2(B) nanostructures were synthesized via a stabilizer-free hydrothermal route and successfully converted to VO2(M) at 350 °C in just 30 min. This process offers a reduced thermal budget compared to established protocols, which generally require temperatures above 400 °C and durations exceeding 1 h. The resulting urchin-like VO2 nanostructures were characterized using a variety of techniques such as XRD, Raman spectroscopy, SEM and DSC to investigate their structural evolution, surface morphology and metal–insulator transition characteristics. The experimental results reveal that VO2(B) predominantly transforms to VO2(M) upon annealing at 350 °C, with minor secondary oxide phases. Furthermore, the annealing at 450 °C led to the complete phase transformation of VO2 to V2O5, indicating the sensitivity of VO2 to annealing temperature. The results show that the insulator-to-metal transition temperature to be ~65 °C, which is lower than that of bulk VO2 (~68 °C), indicating modified transition behavior in the nanostructured samples. These results demonstrate that hydrothermally synthesized VO2(B) can be converted to predominantly VO2(M) by annealing at 350 °C for 30 min, enabling the observation of a reversible metal––insulator transition near 65 °C. © 2026 Serbian Chemical Society. All rights reserved.