Synthesis Of ITO Nanopowders By Co-precipitate Method

With the development of electronic science and technology transparentconducting oxides have been widely used in electronic devices, solar cells,displays, and so on. Indium tin oxide （ITO） has been widely used due to itsexcellent comprehensive property since its discovery in1950. ITO nanoparticlematerial can be used as the main component of transparent conducting ink besidesthe application as the target materials for sputtering deposition of the transparentconducting films. The research on the fabrication of high quality ITO powders isof great significance.In this thesis, ITO nanopowders were prepared by solution co-precipitationand subsequent calcination from SnCl4and InCl3precursors. The co-precipitationmethod has the advantages of simplicity in production, composition controllability,and short production cycle. During experiments the effects of In to Tin mass ratio,chemical environment of reaction, and subsequent calcination on the structure,conductivity, and transparency of the ITO powders were investigated. X-raydiffraction （XRD） and scanning electron microscope were used to characterize thephase composition, morphology, and structure of the ITO powders. Four-proberesistance measuring system was used to measure the electrical property andUV/visible spectrometer was used to characterize the transparency in the visiblerange of the obtained products.Firstly, the effects of the solution chemical environment on theco-precipitation were investigated. Appropriate amount of acid was added into thereaction solution to adjust the reaction rate, where the effects of sulfuric acid,nitric acid, hydrochloric acid, and acetic acid on the precipitation reaction wereinvestigated. The experimental results indicate that the samples prepared in thepresence of acetic acid have smaller particle size （～20nm）, lower electricalresistance （1×10-3-5×10-3/Ω cm）, and higher transparency （～80%） with lesschlorine ions, suggesting that weak acids have better effects on theco-precipitation reaction. The content of O atoms influences the electricalresistance of the products and smaller resistance appears in the O content range40-55at.%.The precipitants were calcined in the temperature range of350-700℃,which indicates that the comprehensive properties of the calcined products werebetter at600℃and decrease with decreasing the temperature below550℃.Theeffects of doping concentration on the structure and property of the obtainedmaterials were investigated by changing the mass ratio of In to Tin in the reaction solution. It is found that lower resistance and higher transparency can be obtainedin the In to Tin ratio range of10:1-11:1while the properties degrade at the ratiosof8:1,9:1, and12:1.Finally, the effects of the ammonia concentration and adding rate, reactiontemperature, ultrasonic treatment, and wash on the precipitated products wereinvestigated. It is indicated that the impurity concentration decreases and thetransparency increases with decreasing the ammonia concentration while theconductivity and transparency decrease with increasing the adding rate ofammonia. The impurity concentration increases with the increase of the reactiontemperature and the products prepared at room temperature show better properties.The introduction of ultrasonic in the reaction process can increase the dispersity ofthe obtained powders and the wash on the precipitated products with ethanol candecrease the agglomeration of the powders during subsequent calcination.In general, the process preparing the ITO nanopowders by co-precipitationwas investigated in this thesis. The methods to control the impurity concentration,crystallinity, dispersity, and property of the ITO nanopowders were established.The ITO nanopowders with diameter about20nm, resistivity of10^-4Ω cm, andtransparency about90%were successfully prepared.