Investigation of preparation method on vanadium oxide thin films thermochromic tendency under high annealing temperature

The effect of investigation method on the vanadium oxide thin film transition temperature have been investigated. Three coating solutions were adopted; first starting from vanadium (V) oxytripropoxide precursors mixed with anhydrous isopropanol with and without tungsten chloride. While the other two solution starts from vanadium metal or vanadium pentoxidemixed with hydrogen peroxide. Spin coating technique was used to prepare the tested films,at spinning speed of 2800 rpm, using (1×1 cm) quartz substrate. The effect of annealing temperature on the films structure were investigated too. The resulting films were characterized through UV-VIS-NIR, SEM, XRD and FTIR. The doping concentration effect on films thermochromic properties was investigated. Introduction Smart windows, defined as the kind of windows that partially prevent the unwanted solar radiation. This property can enhanced by increasing heat gain in wintry weather and decreasing it in warm weather by adopting glasses irradiative and thermal features dynamically [1]. Coating convenient absorbing layer on the surface of the glass can modify the optical properties of this glass by regulating the fallen solar heat flux [2]. Thus smart windows lead to reduced heating freshening and air conditioning energy consumption, size and electric request of the building [3,4]. Smart glasses latest equipment, include thermochromic, electrochromic, photochromic, micro-blind and polymerisolated liquid crystal devices[5]. F. J. Morin in 1959 was firstly discovery of the VO2 transition [6]. At low temperature, VO2 has a monoclinic crystal structure. If VO2 films was heated over the transition temperature (around 68°C), the lattice is changed from the monoclinic to a tetragonal crystal phase, then enabling the material to be IR reflecting. Practically, in addition to VO2, there are corresponding vanadium oxides often resulting from preparation methods, which are commonly known as Magnelli phases VnO2n-1 [7]. The mainvanadium oxide phases are V2O5,VO, VO2 and V2O3, which reveal different oxidation states V 2+ ,V 4+ , V 3+ and (V 5+ ) respectively. Usually, vanadium dioxide thin films are synthesized through physical vapor deposition, chemical vapor deposition and sol-gel method. Sol-gel method is starting from; precursor solution, its transformation into sol and then into gel due to hydrolysis and condensation processes, following by aging, drying and thermal treatment. In fact fabrication of thin films can occur on the gel stage, where the obvious advantage of sol-gel method is the high degree of initial components homogeneity. International Journal of ChemTech Research CODEN (USA): IJCRGG, ISSN: 0974-4290, ISSN(Online):2455-9555 Vol.10 No.9, pp 093-100, 2017 Wesam A ATwej et al /International Journal of ChemTech Research, 2017,10(9): 093-100. 94 Researchers have to pay particular attention to the direct dependence between the synthesis methods and conditions and products physical properties. Furthermore, the film morphology also greatly influences the phase transition characteristics, mainly on the thermal hysteresis loop width. The effect of synthesis conditions on the reaction products is also evident for sol-gel approach [8-10]. Sol-gel technology can also be used to synthesize doped VO2 thin films on fluoride tin oxide [11], aluminum [12], silicon [10], titanium oxide [13], Laminate Films [14]or glass [15] substrates. Furthermore, vanadium pentoxide reduction on the substrate [16, 17] is one of the possible modifications of VO2 sol-gel synthesis, the initial Magnelli phases can be converted into VO2(B) and VO2(M) [17]. Morphology together with particle size and doping are the main parameter that determines the VO2 properties. The various existing ways for VO2 synthesis are quite assort and numerous variations of composition, dimension distributions and material structure can be achieved. This raises new ambitious areas for the scientists. The improvement of known synthetic techniques as well as the development of novel synthesis approaches are very perspective in order to discover modern products with more complicated structures and compositions. The aim of this investigation is fabrication of vanadium oxide W-VO2as thermochromic composite films using the VO2 orW-VO2 coating. Also studying three preparation methods of vanadium oxides thin film, then examine the tungsten chloride doping concentration affection on the transition temperature.