Thermal kinetic analysis of metal–insulator transition mechanism in W-doped VO2

Abstract

Tungsten (W) doping can decrease the phase transition temperature of VO 2 , but underlining reasons are not clear. In this study, differential scanning calorimetry was employed to investigate the kinetics of the solid-solid transition in hydrothermal-synthesized W (X = 0.50, 1.09, 2.58 and 3.81 %)-doped VO 2 nanoparticles. We firstly revealed the W-doping mechanism by combining the classical nucleation kinetics model with isoconversional kinetic analysis and applied them on the solid-solid transition taking place in doping. The experimentally observed large lag in the cooling stage and asymmetry effects of the decreasing temperature on insulator-metal transition and metal-insulator transition can be rationally explained. In the heating stage, W doping decreases free energy barrier (DG*) for homogenous nucleation and reduces geometrical factor (f(H)) and both factors promote the transition and thus lower the phase transition temperature quickly. However, in cooling stage, the free energy barrier (DG het * ) for heterogeneous nucleation was much larger than that of heating stage due to lacking of proper nucleation sites. The effect of decreasing geometrical factor was accompanied with the effect of increasing free energy barrier for homogenous nucleation by doping W. Such a competition mechanism slows down the trend of reducing temperature. It is important to unravel interaction mechanisms of doped W on different VO 2 phases, which is helpful to further tailor kinetic properties of VO 2 phase transition.

Bioinspired Temperature Regulation in Interfacial Evaporation

“…The SSPT from VO 2 (M) to VO 2 (R) is an endothermic process and the SSPT from VO 2 (R) to VO 2 (M) is an exothermic process. In this work, due to the hysteresis of SSPT in the system, there are more VO 2 (M) appears at HTR than the amount VO 2 (R) since superheating above the phase transition temperature is required for the full phase transition from VO 2 (M) into VO 2 (R) 24. For the same reason, more VO 2 (R) appears at LTR since undercooling below the phase transition temperature is required for the full phase transition from VO 2 (R) into VO 2 (M).…”

“…In this work, due to the hysteresis of SSPT in the system, there are more VO 2 (M) appears at HTR than the amount VO 2 (R) since superheating above the phase transition temperature is required for the full phase transition from VO 2 (M) into VO 2 (R). [24] For the same reason, more VO 2 (R) appears at LTR since undercooling below the phase transition temperature is required for the full phase transition from VO 2 (R) into VO 2 (M). Therefore, when the system was in the LTR, most of the NPs in the VO 2 layer were in the R phase (insets of Figure 3b).…”

“…We also demonstrated the spontaneous pyroelectricity generation enabled by such temperature oscillation during the water evaporation. The key enabling component in the system is a layer of thermochromic vanadium dioxide (VO 2 ) nanoparticles (NPs), which show a reversible solid‐state phase transition (SSPT) between monoclinic insulating type VO 2 (M) and rutile metallic type VO 2 (R) as the temperature changes 23–25. This reversible phase transition is accompanied by the enthalpy change as well as the reflectivity change in the near‐infrared (NIR) region.…”

“…The key enabling component in the system is a layer of thermochromic vanadium dioxide (VO 2 ) nanoparticles (NPs), which show a reversible solid-state phase transition (SSPT) between monoclinic insulating type VO 2 (M) and rutile metallic type VO 2 (R) as the temperature changes. [23][24][25] This reversible phase transition is accompanied by the enthalpy change as well as the reflectivity change in the near-infrared (NIR) region. Extensive studies have demonstrated the feasibility of indoor thermal management by applying VO 2 into smart windows due to its reflectivity change upon temperature changes.…”

Effect of Zr Doping on the Magnetic and Phase Transition Properties of VO2 Powder

“…A main peak appeared at 530.59 eV corresponding to a typical lattice O 2− absorption that has been reported for many metal oxides (e.g. TiO 2 and VO 2 ) [31,32]. A peak appeared with a BE of 532.56 eV was assigned to C=O and hydroxyl groups that probably result from contamination of sample [31].…”