Preparation And Optical Properties Of Tungsten-doped Vanadium Dioxide Nanofilms

VO2 is a thermochromic material which optical properties have a large change before and after its phase transition point(68 ?).Based on this characteristic,VO2 has also become a very broad application of functional materials,measuring thermal infrared radiation,infrared pulsed laser radiation protective film,smart windows,thermistors and solar panels,and many other areas have particularly prominent role.However,defects in the practical application of the main phase transition temperature is too high.For practical applications,we need to reduce the phase transition temperature by various means,and experimental methods.In this paper,the sol-gel process is used for preparing tungsten-doped gel film,and its heat treatment under an argon atmosphere to give the final product of tungsten-doped vanadium dioxide nano film.Doping is an important mean to reduce the vanadium oxide thin film phase transition temperature,before and after the doping thin-film photovoltaic performance has a significant difference,the first by a sol-gel method of preparing a gel film on a quartz substrate,keeping all parameters and preparation conditions remain unchanged,change tungsten doping,and then heat-treated under argon get different amounts of tungsten-doped vanadium dioxide nano film.Using X-ray diffraction,scanning electron microscopy,differential scanning calorimetry and UV-Vis-NIR spectrophotometer to test tungsten-doped vanadium dioxide nano film properties.The results show the configuration of different concentrations of vanadium precursor sol,its concentration reported in the literature is changed around 0.125 mol/L,after annealing the resulting nano-films are all standard VO2 film,that small differences in concentrations has no effect Therefore this paper were taken vanadium concentration 0.125 mol/L.Characterized by XRD of a film doped with increasing amounts of tungsten-doped crystal nano film basically unchanged,at(011)20 peak orientation on the case of minor enhancements,which is due to the W ions replace a part of the V ion into the crystal lattice.By scanning electron microscopy,it can be seen that the particle size is between 20-200 nm,the particle size is quite small.When introduced into the protective gas argon gas flow is not the same,different amounts of tungsten-doped vanadium dioxide prepared nanofilms reunion situation is significantly different.Under the same gas flow rate,with the increase in doping,the reunion is more obvious,this is due to the small size of nanoparticles,surface area,surface energy,and therefore prone to agglomeration,sparse population distribution;and when the same amount of tungsten doping air flow is not the same,but less airflow large reunion,the overall distribution-intensive,which is due to air traffic increases could undermine the electrostatic and van der Waals forces between aggregates,reducing the reunion,it could be the gas flow rate increases,with go organic group surface cracking during annealing product,a reducing atmosphere to prevent the film surface reactions,suppressed and agglomeration.The gel was dried to a powder and annealed VO2 powder obtained by differential thermal analysis,that the undoped powder phase transition temperature is 67 ?,tungsten doping 1.5mol%powder phase transition temperature is 37 ?,consistent with the theoretical value,the phase transition temperature decreased significantly.UV-Vis transmittance test,phase transition transmittance decreased significantly,this is because the first phase change,VO2 monoclinic phase,the infrared light through,after the phase transition,VO2 tetragonal phase,infrared light barrier.The degree of change of the transmission nanofilms spin coating can be seen three times better than the nano-second spin-coated films.By thermal hysteresis curve projections,undoped nanofilms phase transition temperature is 55 ?,tungsten doping 0.5mol%nanofilms phase transition temperature is 42 ?,tungsten doping lmol%nanofilms phase transition temperature is 34 ?,tungsten doping 1.5mol%nanofilms phase transition temperature is 32 ?,tungsten doping 2mol%nanofilms phase transition temperature is 25 ?,each tungsten doping nanofilm phase transition temperature is lower than the theoretical value,this is because the nano-particle size effect causes the phase transition temperature is far lower than the theoretical value,but the doping amount of agglomeration occurring between grains increases,resulting in the particles increases,the phase transition temperature decrease is reduced,and scan results of testimony.The paper prepared tungsten doped VO2 phase transition temperature nanofilms significantly decreased tungsten doping effect,small particle size,enabling transmission of the film as a whole,and can further reduce the phase transition temperature,is conducive to practical use.