Phase, Microstructure, Thermochromic, and Thermophysical Analyses of Hydrothermally Synthesized W-Doped VO<sub>2</sub> Nanopowder

Barra, Hamdi Muhyuddin; Chen, Soo Kien; Tamchek, Nizam; Talib, Zainal Abidin; Lee, Oon Jew; Tan, Kar Ban

doi:https://doi.org/10.1155/2021/8582274

Advances in Materials Science and Engineering

On this page

Abstract Introduction Materials and Methods Results and Discussion Conclusions Data Availability Conflicts of Interest Acknowledgments References Copyright Related Articles

Research Article | Open Access

Volume 2021 | Article ID 8582274 | https://doi.org/10.1155/2021/8582274

Phase, Microstructure, Thermochromic, and Thermophysical Analyses of Hydrothermally Synthesized W-Doped VO₂ Nanopowder

Hamdi Muhyuddin Barra,¹Soo Kien Chen,²Nizam Tamchek,²Zainal Abidin Talib,²Oon Jew Lee,³and Kar Ban Tan⁴

Academic Editor: Lingxue Kong

Received04 Jun 2021

Accepted28 Aug 2021

Published13 Sept 2021

Abstract

Vanadium dioxide (VO₂) has great potential as an intelligent architectural glazing system as it can control the amount of light, heat, and solar energy relative to the temperature in the environment. However, the applicability of VO₂ for commercial use is yet to be realized because its phase transition temperature (τ_c) of ∼68°C is too high for use in buildings. A proven strategy to lower its τ_c is by elemental doping. Hence, in this study, hydrothermal synthesis of nanostructured VO₂ was carried out with the introduction of tungsten (W) as a dopant. Furthermore, the effects of W doping on the structural, thermochromic, and thermophysical properties of VO₂ were examined. Using X-ray diffraction (XRD), it was found that the addition of W atoms affected the VO₂ lattice since the crystal structure of VO₂ was changed from monoclinic to tetragonal rutile. Subsequently, this influenced the thermochromic behavior of the prepared VO₂. Based on the differential scanning calorimetry (DSC), doping with tungsten resulted in a significant decrease in τ_c from 66.47°C to as low as 31.64°C. Moreover, W doping affected the thermophysical properties of the samples. Accordingly, an abrupt increase in the thermal conductivities of the doped samples was observed across the transition temperature.

1. Introduction

Energy-saving methods are important in curbing the problem of global climate change. One way to conserve energy is by enhancing energy efficiency, i.e., minimizing avoidable energy losses while maximizing its output [1]. Consequently, one of the areas where efficiency can be greatly improved is in built environments or buildings as they use up a significant amount of energy. In fact, buildings consume about 30–40% of the world’s primary energy, mainly for heating, ventilation, and air conditioning (HVAC), lighting, and appliance usage [2]. However, the majority of this energy is wasted due to the inefficiencies of windows. Since windows easily allow heat to go in or out of a building, more energy is required to use cooling or heating systems to balance the increase or decrease in temperature [3].

A promising avenue in reducing energy expenditure and losses in buildings is the fabrication of energy-efficient windows with the ability to control the throughput of light, heat-carrying infrared (IR) radiation, and solar energy. One way to do this is by coating spectrally selective materials on the surface of windows [4]. By blocking unwanted and regulating solar radiation, usage of HVAC and lighting can be minimized, which can translate into reductions in energy use and greenhouse gas (GHG) emissions.

A prime candidate for this application is the thermochromic compound vanadium dioxide (VO₂), as it has the ability to reversibly change from a semiconductor with a monoclinic structure (M-phase) to a metal with a tetragonal rutile structure (R-phase) at a phase transition temperature (τ_c) of 68°C [5]. As the material undergoes a phase shift, its optical properties also change; i.e., when it is in the VO₂ (M) phase, it is transparent to IR radiation, whereas when it is in the VO₂ (R) phase, it becomes IR reflective [6]. Meanwhile, the transmission of visible light does not change in both phases [7]. Hence, VO₂ has great potential in the fabrication of smart windows.

However, the industrial and commercial use of VO₂ have yet to be realized due to some limiting factors [8]. For instance, the τ_c of VO₂ is still too high for near room temperature usage in buildings. Ideally, VO₂-based windows should reflect heat-carrying IR rays at room temperature (∼25°C) to achieve people’s thermal comfort [9]. Doping VO₂ has been reported to be the most effective way of lowering the τ_c value of VO₂ [10]. Cations such as niobium (Nb⁵⁺), tantalum (Ta⁵⁺), molybdenum (Mo⁶⁺), and tungsten (W⁶⁺), which have a larger radius than V⁴⁺ ion and high valency, are primary candidates for such task [11].

For instance, in the case of tungsten, Long et al. comprehensively discussed the effects of W dopant on the atomic structure of VO₂ and the reduction of τ_c by employing X-ray absorption spectroscopy using synchrotron radiation coupled with first-principle calculations [12]. Accordingly, there is intrinsic symmetry around the local structure of the W atom with a seemingly tetragonal configuration. This propels the distortion and twisting of the asymmetric VO₂ lattice forming rutile-like nuclei that cause a reduction in the thermal activation energy of the phase transition. This is evident in the works of Chen et al. (2012) and Blackman et al. when both groups doped VO₂ with W and reported a reduced τ_c of 35°C and 20°C, respectively [13, 14]. Most recently, W doping was done by Zou et al. (2018) by a combined sol-gel-hydrothermal-annealing process that further reduced τ_c to 27°C with a temperature reduction rate of -22 Cº/at% W [15]. Meanwhile, Hanlon et al. used molybdenum as VO₂ dopant and found that the phase transition temperature of VO₂ decreases to 24°C with a rate of 5 Cº/at% Mo [16]. Moreover, codoping of W and Mo was conducted by Lv et al. (2014), using microwave-assisted HT synthesis, which led to further reduction of τ_c to as low as 17°C [17].

Overall, these studies have mostly reported on the reduction of the transition temperature of VO₂ to near room temperature by elemental doping. However, very few studies have analyzed the effects of doping on the phase transition performance of VO₂. Additionally, there is a notable paucity of studies assessing the effects of doping on the thermophysical properties of VO₂, particularly across its phase transition temperature. Hence, in this work, the effects of tungsten as dopant on the structural and thermochromic properties of VO₂ were examined. In particular, the phase transition performance of doped VO₂ was evaluated by measuring its enthalpy and hysteresis. Further, the effects of the dopant on the thermophysical properties of the prepared nanostructured VO₂ were investigated.

2. Materials and Methods

2.1. Sample Preparation

All chemical reagents in this study were of analytical grade and used without further purification. Differing weight percentages (wt%) of metallic tungsten powder relative to the V precursor were prepared. This was done by dissolving the requisite amount of W in 2 mL hydrogen peroxide (H₂O₂, 30%). The concentration of the dopant relative to the V precursor, wt% (W), was calculated using the following equation:where m(W) is the mass of the dopant and m(V) is the mass of the V precursor. W concentrations of 1, 1.5, 2, and 3 wt% were prepared for the hydrothermal process, and the respective powder products were labeled as VMW1%, VMW1.5%, VMW2%, and VMW3%. Also, the undoped sample was labeled VMW0% to denote the absence of dopant.

The preparation of the undoped sample is reported elsewhere [18]. Meanwhile, to begin the synthesis of the doped samples, 2.4750 g of V₂O₅ was dissolved in 148 mL deionized water under magnetic stirring. H₂C₂O₄ with a mass of 4.9502 was then added while vigorous stirring continued. When the V₂O₅-H₂C₂O₄-H₂O system turned blue-green, the W-H₂O₂ solution was added to it. Afterwards, the solution was transferred into a 240 mL Teflon-lined autoclave when it changed into a reddish color. It was then heated inside an electric oven at a temperature and processing time of 180°C and 24 h, respectively. Then, the blue-black precipitate was collected after cooling it to ambient temperature. Then, it was centrifuged and washed with ethanol and water several times. Finally, the powder was dried at 60°C overnight. Since the produced VO₂ particles were in a metastable state, further heat treatment was employed to obtain the desired thermodynamically stable phase. Hence, the samples were calcined at 650°C in 2 hours under an N₂ environment with heating and cooling rates of 5 C°/min.

2.2. Sample Characterization

The phase and crystal structure of the prepared samples were analyzed by X-ray diffraction using the X’pert Pro PANalytical MPD diffractometer at 2θ values ranging between 20° and 80° at a scanning step rate of 0.017 s⁻¹. Additionally, the morphology of the samples was examined by field-emission scanning electron microscopy (FESEM) using a JEOL-JSM7600F scanning electron microscope at an acceleration voltage of 5 kV. Meanwhile, differential scanning calorimetry (DSC) was employed to measure the obtained powder’s thermochromic properties. This was done by placing an amount of nanopowder in a DSC822e (Mettler Toledo) specimen pan with a temperature accuracy of ±0.20°C. As the temperature was increased from 30°C to 200°C and then decreased from 200°C to 30°C, the heat flow on the sample was measured. Finally, thermal diffusivity was measured using a Netzsch LFA457 light flash apparatus (LFA). This was done by molding the nanopowder samples into pellets with a thickness of 1 mm and a diameter of 10 mm using a hydraulic press.

3. Results and Discussion

3.1. Phase and Structural Analysis

The XRD scans of the hydrothermally prepared undoped and W-doped VO₂ powders after annealing are illustrated in Figure 1. The appearance of a non-VO₂ compound was observed from sample VMW1%, as shown in the presence of V₆O₁₃. These crests gradually diminish as the concentration of the dopant was increased. However, peaks belonging to V_2.4W_0.6O₇ began to appear at wt. percentage of 1.5 wt%. Interestingly, when the concentration of W reached 2 wt%, peaks associated with the tetragonal rutile VO₂ (R) were detected with ICSD code 98-007-1662 of space group P42/mnm. As found in literature, replacing a V site in the VO₂ crystalline structure with the larger W atom causes strong interactions. Subsequently, the asymmetric atoms in the VO₂ lattice rearrange themselves, which leads to the transformation from monoclinic to tetragonal configuration.

Moreover, an enlarged view of the preceding XRD patterns is illustrated in Figure 2 to provide a magnified look at the effects of the doping concentration on the phase formations in VO₂ (M). At 2θ values between 26° and 35°, as many as four events or changes (labeled I, II, III, and IV) in the XRD plots can be observed. Firstly, in event I, the (0 1 1) peak of VO₂ (M) at 26.90° deteriorated, and a new peak at 27.11°, which belongs to V_2.4W_0.6O₇, appeared. In event II, the VO₂ (M) peak at 27.86° shifted position gradually to 27.65°, which can be indexed to the VO₂ (R) peak with Miller indices (hkl) of (1 1 0). Also, the appearance and abrupt disappearance of the peak associated with V₆O₁₃ can be seen in event III. The presence of V₆O₁₃, which signified the occurrence of oxidation in an otherwise inert nitrogen atmosphere, may have stemmed from the residual H₂O₂ molecules, which were not fully dissolved during the hydrothermal synthesis nor removed through the washing and centrifugation processes. Potentially, these molecules were adsorbed in the VO₂ (B) molecules and tended to reoxidize the VO₂ particles into V₆O₁₃ during the heating treatment. Finally, in event IV, a VO₂ (M) peak gradually diminished while a new peak belonging to VO₂ (R) emerged. This shifting of peak to lower 2θ value is mainly due to the replacement of W atoms on the V sites. Considering that tungsten has a greater atomic radius (1.37 Å) compared with vanadium atom (1.34 Å), this can potentially result in the increase of adjacent interplanar distance (d-spacing). Hence, the peak position movement is towards the left because there is an inverse proportionality relationship between the d-spacing and 2θ values based on Bragg’s law.

Additionally, the samples’ full width at half maximum (FWHM) and lattice properties at the peak with the greatest intensity were measured and summarized in Table 1. It can be observed that the quality of crystallization diminished as the W content was increased to 2 and 3 wt.%. Specifically, the FWHM widened from 0.1299° to 0.1948° with increasing W concentration. A factor that affected the FWHM was the crystallite size which significantly decreased from 81.5 nm (for the undoped sample) to 50.1 nm (for sample VMW3%). Based on the transformation of VO₂ (B) to VO₂ (R) during the annealing process, the increase in temperature resulted in the breakage of the interconnections between the edge-sharing and corner-sharing octahedra in the VO₂ (B) crystal lattice. Then, the octahedra underwent reorientation to form the rutile tetragonal structure, which has a smaller crystallite size. Moreover, the addition of tungsten accelerated this process. As elucidated in the work of Zhang et al. (2015), distortions caused by the tungsten atoms in the doped VO₂ (B) hasten the breakage of the interconnecting V-O octahedra [19]. With prolonged heating during the annealing stage, the VO₂ (B) transformed to VO₂ (R) at a faster rate, which resulted in the growth of VO₂ (R) with reduced crystallite size.

Another factor that caused the broadening of peaks was the internal strain in the VO₂ lattice which increased from 0.196 to 0.322. This increase is mainly due to the difference in the atomic radius of W and V. By replacing V sites with W atoms, which have a greater radius, distortions in the V-V and V-O bonds in the VO₂ (M) crystals transpire. With increasing dopant concentration, more V sites were replaced with W atoms, thus resulting in greater lattice strain. This finding is further supported by the measurement of the interplanar spacing in the undoped and W-doped samples. As shown in the rightmost column of Table 1, the d-spacing increased with increasing W weight percentage. Indeed, this shows the successful partial substitution of V atoms with W atoms in the VO₂ (M) crystal structure.

Additionally, the morphologies of the synthesized W-doped VO₂ were examined using field-emission scanning electron microscopy analysis. The FESEM scans of the samples are given in Figure 3. Similar to sample VMW0%, all the doped samples showed the formation of spherical shapes, albeit at larger sizes. Grain growth mechanism may have caused these changes in the morphology during the heat treatment process. Correspondingly, dissociation of the vanadium and oxygen atoms causes the disordering and breakage of the VO₂ (B) nanobelts. Then, the crystalline structure is reconfigured and transformed into the monoclinic VO₂ (M) or into the tetragonal VO₂ (R) with the addition of tungsten. After 2 hours of annealing, coalescing of the nanoparticles occurs. Agglomeration stage follows, whereby oblate, spherical, and/or plate-like shaped particles are formed. For samples VMW0%, VMW1%, VMW1.5%, VMW2%, and VMW3%, the measured average diameters of these spheroids were 0.24, 3.08, 2.17, 1.51, and 0.89 μm, respectively. According to Chen et al. (2014), this increase in grain size is a prominent feature of W doping on VO₂ [20]. Seemingly, samples with wt.% of 1% and 1.5% had rough surfaces compared with the undoped and the other doped samples. This may be due to the presence of V₆O₁₃ based on their XRD scans. Meanwhile, the formation of nanorods can be noticed in Figures 3(c) and 3(d) when the doping reached 2 and 3 wt%. The widths of these rods were as low as 161 nm for VMW2% and 101 nm for VMW3%. Based on the diffractograms of these samples, these rods may contain the compound V_2.4W_0.6O₇.

(a)

(b)

(c)

(d)

(e)

3.2. Influence on Thermochromic Properties

The thermochromic behavior of W-doped VO₂ can be evaluated using the DSC curve of the samples in Figure 4. As seen, a change in the position of the peaks can be readily observed as the concentration of W was increased. Particularly, the peaks shifted to the left, indicating the reduction of the phase transition temperature. As elaborately discussed by Tan et al. (2012), the local structure of the tungsten atom has intrinsic symmetry with a tetragonal-like configuration [21]. When added to a VO₂ (M), W propels the distortion of the VO₂ lattice and twisting of the asymmetric V-V bonds, resulting in the formation of rutile-like nuclei. Consequently, this lowers the thermal activation energy, thereby causing the reduction of the phase transition. Also, sample VMW3% exhibited two sharp peaks at 31.64°C and 51.99°C. These lower phase transition temperatures may be caused by the increase in VO₂ (R) contained in the sample compound as evidenced in the sample’s XRD scan in Figure 1. Also, as reported by Xu et al. (2020), the presence of different-shaped VO₂ nanoparticles can lead to multiple phase transition peaks [22]. Indeed, nanoparticles with differing shapes and sizes can be observed in sample VMW3% in Figure 3(e). However, in the cooling direction, only a single peak was observed. This can be explained through the work of Zou et al. (2018). Accordingly, heating a W-doped VO₂ (M) nanoparticles causes recrystallization which may transform the nanoparticles into larger-sized VO₂ [15]. By heating the sample to 200°C during the heat flow measurement in the DSC, larger-sized VO₂ may have formed. Subsequently, this resulted in higher phase transition temperature in the cooling direction with a single peak.

Furthermore, the measured values of the phase transition temperatures of the samples based on the DSC curve are recorded in Table 2. Correspondingly, τ_c significantly decreased from 66.47°C to 47.35°C when the W concentration was increased to 3%. The decrease in the phase transition temperature can be attributed to the increase in lattice strain (Table 1) as well as the growth of VO₂ (R), as evidenced by the XRD scan (Figure 1). Meanwhile, to determine the heat of metal-to-semiconductor transition and strength of phase change, the enthalpies and hysteresis of the samples were measured (see Table 2). As seen, a large increase in hysteresis is observed as the doping wt.% increases. Since hysteresis is mainly affected by crystallinity and grain size, the high hysteresis in the doped samples may have resulted from the low quality of crystallization due to the presence of impurities in the forms of V₆O₁₃ and V_2.4W_0.6O₇ (see Figure 2) as well as their large grain size (refer to Figure 3).

Meanwhile, a decrease in enthalpy can be observed when 1 wt% W was added to the VO₂ sample. Then, an increasing trend occurred when the wt% of the dopant was increased to 2%. Finally, the heat of metal-semiconductor phase transition (MST) decreased when the W was at 3 wt.%. The trends in τ_c and ΔH of the samples are summarized in Figure 5. As seen, both the phase transition temperatures and enthalpies of all doped samples were lower compared to the undoped sample. This is primarily due to the decrease in the thermal activation energy when W was introduced in the VO₂ (M) lattice. Based on the work of Liang et al. (2016), the V-V bonds in VO₂ (M) are arranged with interval distances of 2.65 and 3.12 Å, while in VO₂ (R), the V-V intervals are equidistant at 2.87 Å [23]. Accordingly, partial substitution of V atoms with W atoms, whose radius is greater, results in the shrinking of the V-V bond intervals. Thus, a decrease in the structural difference between the M- and R-phases of VO₂ emerges. Consequently, the activation energy of the metal-to-semiconductor transition decreases; hence, τ_c and ΔH of the doped sample are lower compared with the undoped VO₂ (M). Nonetheless, the values of the enthalpies in this work are closer to the values for bulk VO₂ (37.38 J/g – 51.85 J/g) [24]. Moreover, the decreasing trend in τ_c is mainly due to the increase in lattice strain, as shown in Table 1. Meanwhile, an increase in the enthalpy from 1 to 2 wt.% may be due to the removal of impurity in the form of V₆O_13, as displayed in the XRD pattern in Figure 2. Meanwhile, the decrease in enthalpy when the W concentration was changed from 2 to 3 wt.% can be potentially caused by the grain size effect considering that sample VMW3% has a greater grain size than VMW2%. Reasonably, the large grain size of VMW3% may contain structural defects or more oxygen vacancies, which have been reported to cause a decrease in the phase transition temperature and the rate of phase transition [25].

3.3. Influence on Thermophysical Properties

The effects of introducing a tungsten dopant on the thermophysical properties of VO₂ were carried out using the microflash method. Specifically, the thermal diffusivity (α) of the samples at temperatures of 25, 50, 100, and 150°C was measured, and the results are plotted in Figure 6. Accordingly, the changes in α from 25 to 50°C, 50 to 100°C, and 100 to 150°C were 0.091, 0.210, and 0.027 mm²/s. Hence, it can be inferred that the heat transferring ability of the highly pure VO₂ (M) significantly increased across the phase transition temperature. Apart from sample VMW1%, an increase in α was still discernible across the metal-to-semiconductor transition temperature of the doped samples. Specifically, the measured Δα from 50 to 100°C were 0.113, 0.157, and 0.07 for samples with W concentrations of 1.5, 2, and 3 wt%. Meanwhile, doping generally resulted in a decrease in thermal diffusivity at a temperature above 25°C. As shown in Table 1, the d-spacing of the doped samples increased, which could result in the decrease of the transfer of heat in the VO₂ lattice.

Moreover, the thermal conductivity (κ) of the samples was calculated using the following equation:where ρ is the material’s density and C_p is the heat capacity. The measured densities of the pelletized samples, namely, VMW0%, VMW1%, VMW1.5%, VMW2%, and VMW3%, were 2.75, 3.20, 3.23, 3.23, and 3.31 g/cm³, respectively. Inasmuch as these pellets were obtained by the hydraulic pressing of porous nanopowder samples, their densities were lower than the theoretical density of VO₂ (M), which is 4.67 g/cm³. The heat capacities, on the other hand, were determined from the DSC data in Figure 4, using the following equation:where Q/m is the measured heat flow in the DSC curve and dT/dt is the temperature gradient employed in the DSC scan. The resulting measurements of κ are plotted in Figure 7.

Correspondingly, the profiles of these plots are similar to the results of Oh et al., albeit with lower values, which is primarily due to the low densities used in calculations [26]. Accordingly, a considerable increase in thermal conductivity across τ_c can be observed. Particularly, for the undoped VO₂, κ increased from 2.140 to 3.163 W/m•K as the temperature was increased from 50 to 100°C. This corresponded to a Δκ of 1.023 W/m•K, which is greater than Δκ from previous results on VO₂ bulk and nanobeams [27]. Meanwhile, for W-doped samples, the thermal conductivities at 25°C were very close to that reported by Oh et al. for VO₂ bulk. Also, an incremental change in κ occurred from 25 to 50°C. Then, a bigger jump can be observed across the phase transition temperature. Specifically, Δκ with values of 0.297, 1.424, 1.329, and 1.288 W/m•K were recorded. In general, these values are greater compared to previous findings [13, 27]. This increase in thermal conductivity is possibly caused by the absence of grain boundary defects, which tend to decrease the thermal conductivity of a material.

4. Conclusions

Investigation of the influences of elemental doping on the structural, morphological, thermochromic, and thermophysical properties of VO₂ nanoparticles was carried out. Accordingly, the introduction of W shifted some of the peak locations in the XRD scans of the samples, which indicated a phase transformation from VO₂ (M) to VO₂ (R). This shift in phase was caused by the increase in the lattice strain of the VO₂ crystal structure. Also, an increase in grain size was observed in the doped sample. More importantly, doping resulted in the decrease of the phase transition temperature of VO₂ from 66.47°C to as low as 31.64°C. However, a decrease in the enthalpy was observed, which signified a decrease in the transition strength. This was potentially caused by many factors such as lower crystallinity, an increase in lattice strain, and the presence of impurities. In addition, W doping was found to influence the thermophysical properties of VO₂. In particular, the thermal diffusivity and thermal conductivity of the doped VO₂ increased noticeably across its phase transition temperature.

Data Availability

The data used to support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Acknowledgments

The authors would like to thank the Universiti Putra Malaysia for the financial support of this research under Putra Grant GP-IPS (Grant no. 9501500).

References

B. Baatz, G. Relf, and S. Nowak, “The role of energy efficiency in a distributed energy future,” The Electricity Journal, vol. 31, no. 10, pp. 13–16, 2018.
View at: Publisher Site | Google Scholar
C. G. Granqvist, P. C. Lansåker, N. R. Mlyuka, G. A. Niklasson, and E. Avendaño, “Progress in chromogenics: new results for electrochromic and thermochromic materials and devices,” Solar Energy Materials and Solar Cells, vol. 93, no. 12, pp. 2032–2039, 2009.
View at: Publisher Site | Google Scholar
M. Kamalisarvestani, S. Mekhilef, and R. Saidur, “Analyzing the optical performance of intelligent thin films applied to architectural glazing and solar collectors,” in Sustainability in Energy and Buildings, A. Hakansson, M. Hojer, R. Howlett, and L. Jain, Eds., pp. 813–826, Springer, Berlin, Germany, 2013.
View at: Publisher Site | Google Scholar
Y. Gao, H. Luo, Z. Zhang et al., “Nanoceramic VO₂ thermochromic smart glass: a review on progress in solution processing,” Nano Energy, vol. 1, no. 2, pp. 221–246, 2012.
View at: Publisher Site | Google Scholar
M. M. Seyfouri and R. Binions, “Sol-gel approaches to thermochromic vanadium dioxide coating for smart glazing application,” Solar Energy Materials and Solar Cells, vol. 159, pp. 52–65, 2017.
View at: Publisher Site | Google Scholar
J. Wu, W. Huang, Q. Shi et al., “Effect of annealing temperature on thermochromic properties of vanadium dioxide thin films deposited by organic sol-gel method,” Applied Surface Science, vol. 268, pp. 556–560, 2013.
View at: Publisher Site | Google Scholar
L. Long and H. Ye, “How to be smart and energy efficient: a general discussion on thermochromic windows,” Scientific Reports, vol. 4, pp. 1–10, 2014.
View at: Publisher Site | Google Scholar
S. Li, G. A. Niklasson, and C. G. Granqvist, “Nanothermochromics: calculations for VO₂ nanoparticles in dielectric hosts show much improved luminous transmittance and solar energy transmittance modulation,” Journal of Applied Physics, vol. 108, Article ID 063525, 2010.
View at: Publisher Site | Google Scholar
M. Kamalisarvestani, R. Saidur, S. Mekhilef, and F. S. Javadi, “Performance, materials and coating technologies of thermochromic thin films on smart windows,” Renewable and Sustainable Energy Reviews, vol. 26, pp. 353–364, 2013.
View at: Publisher Site | Google Scholar
P. Kiri, G. Hyett, and R. Binions, “Solid state thermochromic materials,” Advanced Materials Letters, vol. 1, no. 2, pp. 86–105, 2010.
View at: Publisher Site | Google Scholar
S. Wang, M. Liu, L. Kong, Y. Long, X. Jiang, and A. Yu, “Recent progress in VO₂ smart coatings: strategies to improve the thermochromic properties,” Progress in Materials Science, vol. 81, pp. 1–54, 2016.
View at: Publisher Site | Google Scholar
R. Long, B. Qu, R. Tan et al., “Identifying structural distortion in doped VO₂ with IR spectroscopy,” Physical Chemistry Chemical Physics, vol. 14, no. 20, pp. 7225–7228, 2012.
View at: Publisher Site | Google Scholar
J. Chen, X. Liu, X. Yuan et al., “Investigation of the thermal conductivities across metal-insulator transition in polycrystalline VO₂,” Chinese Science Bulletin, vol. 57, no. 26, pp. 3393–3396, 2012.
View at: Publisher Site | Google Scholar
C. S. Blackman, C. Piccirillo, R. Binions, and I. P. Parkin, “Atmospheric pressure chemical vapour deposition of thermochromic tungsten doped vanadium dioxide thin films for use in architectural glazing,” Thin Solid Films, vol. 517, no. 16, pp. 4565–4570, 2009.
View at: Publisher Site | Google Scholar
J. Zou, X. Chen, and L. Xiao, “Phase transition performance recovery of W- doped VO₂ by annealing treatment,” Materials Research Express, vol. 5, Article ID 065055, 2018.
View at: Publisher Site | Google Scholar
T. J. Hanlon, J. A. Coath, and M. A. Richardson, “Molybdenum-doped vanadium dioxide coatings on glass produced by the aqueous sol-gel method,” Thin Solid Films, vol. 436, no. 2, pp. 269–272, 2003.
View at: Publisher Site | Google Scholar
W. Lv, D. Huang, Y. Chen, Q. Qiu, and Z. Luo, “Synthesis and characterization of Mo-W co-doped VO2(R) nano-powders by the microwave-assisted hydrothermal method,” Ceramics International, vol. 40, no. 8, pp. 12661–12668, 2014.
View at: Publisher Site | Google Scholar
H. M. Barra, S. K. Chen, N. Tamchek, Z. A. Talib, O. J. Lee, and K. B. Tan, “Nanostructured VO₂ (A) and VO₂ (M) derived from VO₂ (B): facile preparations and analyses of structural, thermal, optical and thermophysical properties,” Materials Science, vol. 27, no. 3, pp. 269–275, 2021.
View at: Publisher Site | Google Scholar
Y. Zhang, X. Tan, C. Huang, and C. Meng, “Hydrothermal treatment with VO₂(B) nanobelts for synthesis of VO₂(A) and W doped VO₂(M) nanobelts,” Materials Research Innovations, vol. 19, no. 4, pp. 295–302, 2015.
View at: Publisher Site | Google Scholar
Z. Chen, Y. Gao, L. Kang, C. Cao, S. Chen, and H. Luo, “Fine crystalline VO₂ nanoparticles: synthesis, abnormal phase transition temperatures and excellent optical properties of a derived VO₂ nanocomposite foil,” Journal of Materials Chemistry, vol. 2, no. 8, pp. 2718–2727, 2014.
View at: Publisher Site | Google Scholar
X. Tan, T. Yao, R. Long et al., “Unraveling metal-insulator transition,” Science. Reports. UK, vol. 2, pp. 1–6, 2012.
View at: Publisher Site | Google Scholar
C. Xu, G. Liu, M. Li et al., “Optical switching and nanothermochromic studies of VO₂ (M) nanoparticles prepared by mild thermolysis method,” Materials & Design, vol. 187, Article ID 108396, 2020.
View at: Publisher Site | Google Scholar
S. Liang, Q. Shi, H. Zhu, B. Peng, and W. Huang, “One-step hydrothermal synthesis of W-doped VO₂ (M) nanorods with a tunable phase-transition temperature for infrared smart windows,” ACS Omega, vol. 1, no. 6, pp. 1139–1148, 2016.
View at: Publisher Site | Google Scholar
Y. Chen, S. Zhang, F. Ke et al., “Pressure-temperature phase diagram of vanadium dioxide,” Nano Letters, vol. 17, no. 4, pp. 2512–2516, 2017.
View at: Publisher Site | Google Scholar
J. Y. Suh, R. Lopez, L. C. Feldman, and R. F. Haglund, “Semiconductor to metal phase transition in the nucleation and growth of VO₂ nanoparticles and thin films,” Journal of Applied Physics, vol. 96, no. 2, pp. 1209–1213, 2004.
View at: Publisher Site | Google Scholar
D. Oh, C. Ko, and S. Ramanathan, “Thermal conductivity and dynamic heat capacity across the metal-insulator transition in thin film VO₂,” Applied Physics Letters, vol. 96, pp. 1–4, 2010.
View at: Publisher Site | Google Scholar
S. Lee, K. Hippalgaonkar, F. Yang et al., “Anomalously low electronic thermal conductivity in metallic vanadium dioxide,” Science, vol. 355, no. 6323, pp. 371–374, 2017.
View at: Publisher Site | Google Scholar

Copyright

Copyright © 2021 Hamdi Muhyuddin Barra et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

PDF Download Citation

Download other formats

Order printed copies