Measurement of the hysteretic thermal properties of W-doped and undoped nanocrystalline powders of VO2

Abstract

Hysteresis loops exhibited by the thermal properties of undoped and 0.8 at.% W-doped nanocrystalline powders of VO2 synthesized by means of the solution combustion method and compacted in pellets, are experimentally measured by photothermal radiometry. It is shown that: (i) the W doping reduces both the hysteresis loops of VO2 and its transition temperature up to 15 °C. (ii) The thermal diffusivity decreases (increases) until (after) the metallic domains become dominant in the VO2 insulating matrix, such that its variation across the metal-insulation transition is enhanced by 23.5% with W-0.8 at.% doping. By contrast, thermal conductivity (thermal effusivity) increases up to 45% (40%) as the metallic phase emerges in the VO2 structure due to the insulator-to-metal transition, and it enhances up to 11% (25%) in the insulator state when the local rutile phase is induced by the tungsten doping. (iii) The characteristic peak of the VO2 specific heat capacity is observed in both heating and cooling processes, such that the phase transition of the 0.8 at.% W-doped sample requires about 24% less thermal energy than the undoped one. (iv) The impact of the W doping on the four above-mentioned thermal properties of VO2 mainly shows up in its insulator phase, as a result of the distortion of the local lattice induced by the electrons of tungsten. W doping at 0.8 at.% thus enhances the VO2 capability to transport heat but diminishes its thermal switching efficiency.

High quality VO2 thin films synthesized from V2O5 powder for sensitive near-infrared detection

“…The analysis of the crystal structure is further studied by XRD, as shown in Fig. 4 b. XRD patterns of the film confirms the presence of highly crystalline VO 2 structure, exhibiting two indexed peaks (JCPDS 82-0661), (011) and (022) respectively, located at ~ 27.9° and ~ 57.5° with narrow full width half maximum of ~ 0.15° and ~ 0.3°, consistent with the monoclinic VO 2 structure 17 , 26 . The strong diffraction peak at ~ 27.9° (011) of monoclinic VO 2 suggests that the film has a preferential orientation (011).…”

“…Figure 4 a shows high resolution XPS spectrum of V 2p and O 1 s collected from the final film structures. The V 2p spectrum shows the main peaks of 2p 3/2 centered at 516.1 eV and 2p 1/2 centered at 523.7 eV, which corresponds to the V 4+ oxidation state 11 , 17 , 47 . The small shoulder peak at 517.3 eV is attributable to V 5+ ions due to surface oxidation of the VO 2 thin films or the presence of minor component of V 2 O 5 11 , 17 , 47 The O 1 s spectrum can be deconvoluted into two peaks at 529.9 and 531.9 eV, which correspond to VO 2 and CO 2 , H 2 O, respectively.…”

“…The underlying physical picture of the MIT process has been studied by both theoretical and in situ experimental studies 6 – 8 . Moreover, the change in crystal structure is simultaneously accompanied by colossal changes in the electrical 8 – 10 , optical 11 – 14 , magnetic 15 , and thermal properties 16 , 17 . These properties make VO 2 promising in applications in smart windows 14 , 18 , 19 , optical modulators 20 , gas sensors 21 , memory devices 22 , photodetectors 23 and so forth 24 , 25 .…”

“…On the other hand, magnetron sputtering 8 , 12 – 14 , pulsed laser deposition 22 , 33 and molecular beam epitaxy 34 , are usually used to synthesize epitaxial films of VO 2 (constructed by the nanoparticles). Various factors that affect the MIT behavior of the resultant VO 2 have also been extensively investigated, including size 35 , morphology 2 , 12 , 13 , oxygen defect 22 , 36 , 37 , hydrogen 15 , and chemical doping 17 , 30 , 38 , etc.…”

Facile Solution Process of VO2 Film with Mesh Morphology for Enhanced Thermochromic Performance

“…These layers include TiO 2 [19,20], V 2 O 5 [21], SiO 2 [22], SiN x [23], HfO 2 [24], ZnO [25], and so on. There is some strain between these layers and the VO 2 film, which will have an important effect on the band structure of VO 2 and thus control the phase transition temperature [26][27][28][29][30][31][32][33]. However, the additional protective layer always leads to the deteriorated optical performance of VO 2 film with reduced solar modulation efficiency.…”