Controllable Preparation Of Thermochromic Vanadium Dioxide Thin Films And Study Of Regulate Phase Transition Temperature

Rutile M phase vanadium dioxide(VO2) displays a phase transition from a semiconductor phase to a metallic phase(MIT) at a critical temperature of 68 ?,accomPanied by a reversible abrupt change in optical transmittance. So,the ability to adjust the sunlight transmittance make the VO2 potentially useful for ‘efficient?energy conservation?smart' optical switches windows. However,M phase vanadium dioxide(VO2) still have some problems. Firstly, it is difficult to be prePared. Secondly, the optical transmittance isn't good enough and the phase transition temperature is still too high for optical switches windows.In the study, we used inorganic sol-gel method to prePare V2O5 films on the fused silica substrates by dip coating. Then VO2 films can be gained by high vacuum annealing. Characterization methods including XRD, SEM, UV-Vis-NIR were used to study the influence of oxygen Partial pressure,annealing temperature,different doping ratio, second high vacuum annealing and other factors on the structure, surface morphology, optical properties and transition temperature of the VO2 films. The results were showed as follows:(1)The phase-pure V2O5 thin films which were preParation by inorganic sol-gel method,were annealing treatment under different oxygen Partial pressure. Found under the same heating system(3 ?/min, 510 ?keep warm for 5 h),the oxygen Partial pressure have important influence on crystal structure and optical properties of vanadium oxide thin films.Under 280 Pa vacuum degree,we can get B phase vanadium dioxide film(VO2);Under 260 Pa vacuum degree,get M phase vanadium dioxide(VO2) film; Under 240 Pa vacuum degree,get M phase vanadium dioxide(VO2) and V2O3 phase film; Under 220 Pa vacuum degree,get V2O3 phase film.(2)The annealing temperature have great influence on film properties. With the increase of temperature, the decomposition degree of V2O5 gradually increases, made the VO2 sample which were obtained under 550 ? has the strongest diffraction peak. With the increase of heat temperature, the crystallization degree of vanadium dioxide thin film gradually increase, crystal growing, formed island, rod of crystal under the condition of 550 ?.Heat preservation and the influence of temperature on the properties of thin films are different. The film which were obtained under 510 ? has the highest sun modulation caPability,which is 4.9%; The film which were obtained under 530 ? has the highest optical performance, the average of visible light filtering is 15.04%, the infrared light modulation efficiency in 2000 nm is 61.1%; The film which were obtained under 550 ? has the minimum phase transition temperature,which is 45.9 ?.(3) In the vanadium dioxide thin film,which were preParation by molten inorganic sol-gel method, for a doping tungsten atoms effective implementation.To achieve the purpose of reduces the phase transition temperature. With the increase of mineral admixture, the phase transition temperature(TC) of vanadium dioxide thin film is gradually reduced. When the tungsten content 0?x?1, the phase transition temperature of vanadium dioxide thin film-13.9 ? / at. % W cooling efficiency. When the tungsten content 1?x?1.5, the phase transition temperature of vanadium dioxide thin film-23 ? / at. % W cooling efficiency.(4) This experiment adopts the secondary vacuum annealing method, under the condition of low temperature(about 300 ?), With the introduction of oxygen vacancy, cause tiny distortion of crystal lattice, In the case of basic does not reduce the sun's rays modulation efficiency, reduces the phase transition temperature of the vanadium dioxide thin film. Not doped samples, the phase transition temperature from 64.7 ?to 59.8 ?, 2000 nm modulation caPacity fell 1.9%, the sun's rays modulation efficiency is 3.78%, basic didn't change;Mixed amount to 1% of the sample, the phase transition temperature from 47.5 ?to 42.8 ?, 2000 nm modulation ability, 4.8%, and the sunlight modulation efficiency is 3.38%, basic didn't change.Therefore, in the case of basic does not reduce the sun's rays modulation efficiency, this method can be used to further reduce the phase transition temperature of the doped vanadium dioxide film, makes the film phase transition temperature close to room temperature, achieve energy smart window using conditions.