Studies On The Preparation Of Nanometer VO₂ Powder And The Effects Of Doping On Its Phase-Tansition Properties

VO2 is a typical thermochromic compound, the phase transition temperature is 68 C. With the increase of temperature, it has metal-to-semiconductor transition at 68 C, and its physical properties change, too. For example, electrical resistance has 4-5 magnitude abrupt changes, accompanied by abrupt changes in magnetic susceptibility, optical index of refraction transmissivity, and reflectivity and it has infrared screen function. The importance is that its phase transition temperature can be changed by doping. Therefore, VO2 has great application potentials, such as buildings' solar temperature-control devices, photo-electricity switch materials, thermistor materials, eraserable optical store materials, the protective devices for laser blindly weapons, photo-chromic materials, and modulator of micro-weave radiation, etc. At present, there have been many studies on VO2 film and, to some extent, its application is limited. But VO2 powder has greater application areas and prospects. Recently, it has been found that nano VO2 has much better physical properties. Hence, studies focusing on VO2 powder have very important theoretical and realistic meanings.Based on rich Vanadium resource in Panzhihua, for the first time, only-doping and multi-doping nano VO2 through thermal decomposition have been produced, electricity and optics properties of VO2 on different technological and experimental conditions studied, thermal decomposition process of precursor, the structure and form of nano VO2, and the change of electron band structure after doping analyzed systematically by TG-DSC, XRD, TEM, and XPS techniques. The dissertation gets valuable results. (1). For the first time, by using industry V2O5 powder as raw material through H2C2O4 reduction, VO(C2O4)2 H2O and corresponding doping precursor have been produced. The method is simple and easy to repeat.(2). The particle size of nano VO2 produced after thermo decomposition is 20~30nm, and its distribution is even, ingredient of VO2 is pure, its phase transition temperature is 69.5 C,and its resistance abrupt change reaches two magnitudes, it has obvious screen function within near infrared ray, and it has good thermo-chromic stability. (3).Nano VO2 powder doped with Molybdenum and Molybdenum-Fluorine have been produced and the minimum temperature is 40 C. The phase transition temperature of VO2 powder is decreased remarkably by multi-doping of Molybdenum-Fluorine.