Nanostructured VO2 (A) and VO2 (M) Derived from VO2 (B): Facile Preparations and Analyses of Structural, Thermal, Optical and Thermophysical Properties

Abstract

Vanadium dioxide (VO₂) is an interesting compound that exists in different polymorphic phases with varying characteristics and potential applications. In this study, fabrication and property analyses of three VO₂ polymorphs, namely VO₂ (B), VO₂ (A), and VO₂ (M), are described. Specifically, VO₂ (B) was prepared via hydrothermal method under a low synthesis temperature of 180 °C and a fast processing time of 24 h. In addition, VO₂ (A) and VO₂ (M) were derived from the as-synthesized VO₂ (B) using sequential hydrothermal treatment and calcination process, respectively. From the field-emission scanning electron microscope (FESEM) scans, belt-like VO₂ (B) nanoparticles with dimensions of as low as 35 × 130 nm² were formed. Further, hydrothermal treatment of the as-synthesized VO₂ (B) resulted to a flower-shaped VO₂ (A) due possibly to an oriented attachment mechanism. Meanwhile, annealing of the VO₂ (B) sample caused granular growth that produced plate-like and oblate shaped VO₂ (M) with dimensions of 135 to 306 nm in diameter and 28 to 37 nm in thickness. Moreover, the thermochromic properties of the samples were examined using differential scanning calorimetry (DSC) while the thermophysical properties of the samples were measured via microflash method. Accordingly, the prepared VO₂ (A) and VO₂ (M) samples exhibited phase transition behavior at 168.37 °C and 68.6 °C, respectively. Subsequently, changes in the thermophysical properties of each sample can be observed across the measured transition temperature. In particular, an increase in both the thermal diffusivity and thermal conductivity of VO₂ (M) can be observed when the temperature was raised from 50 °C to 100 °C. On the other hand, there is a noticeable decrease in the thermal conductivity of VO₂ (A) when the temperature was increased from 150 °C to 200 °C.