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Issue 17, 2017
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Particle size, morphology and phase transitions in hydrothermally produced VO2(D)

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Different morphologies and sizes of VO2(D) particles were synthesised via hydrothermal synthesis using ammonium metavanadate (NH4VO3) or vanadium pentoxide (V2O5) as a vanadium precursor. By adjusting the concentration of vanadium precursors and the pH of the starting solution, a variety of morphologies and sizes of VO2(D) particles from 20 nm to 3 μm could be produced. A flower-shape morphology was obtained under strongly acidic conditions, passing through star-shape particles of 1 μm at pH 2.5 and finally obtaining homogeneous round balls of around 3 μm at pH 6.9. Nanoparticles were produced hydrothermally using V2O5 as a precursor and hydrazine as a reducing agent. The transition from VO2(D) to thermochromic VO2(R) in micron scale particles occurred at 350 °C under vacuum. However, the nanoparticles of VO2(D) had a significantly lower VO2(D) to thermochromic VO2(R) transition temperature of 165 °C after annealing for only a few minutes. This is, to our knowledge, the lowest annealing temperature and time reported in the literature in order to obtain a thermochromic VO2 material via another VO2 phase. After the conversion of VO2(D) microparticles to thermochromic VO2(R), the metal to insulator transition temperature is 61 ± 1 °C for the heating cycle and 53 ± 1 °C for the cooling cycle. However, VO2(R) nanoparticles showed a significantly reduced metal insulator transition temperature of 59 ± 1 °C and 42 ± 1 °C for the cooling cycle lower than that reported in the literature for bulk VO2. This is important due to the need for having a compound with a switching temperature closer to room temperature to be used in smart window devices for energy consumption. W-VO2(D) star shape microparticle samples were prepared using 2–7 at% of the dopant (using ammonium metavanadate as a precursor), although unexpectedly this does not seem to be a viable route to a reduced metal to insulator transition in this system.

Graphical abstract: Particle size, morphology and phase transitions in hydrothermally produced VO2(D)

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The article was received on 16 Jun 2017, accepted on 21 Jul 2017 and first published on 21 Jul 2017

Article type: Paper
DOI: 10.1039/C7NJ02165H
Citation: New J. Chem., 2017,41, 9216-9222
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    Particle size, morphology and phase transitions in hydrothermally produced VO2(D)

    D. Teixeira, R. Quesada-Cabrera, M. J. Powell, G. K. L. Goh, G. Sankar, I. P. Parkin and R. G. Palgrave, New J. Chem., 2017, 41, 9216
    DOI: 10.1039/C7NJ02165H

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