Synthesis of Tin Oxide Nanocrystalline Phases Via Use of Tin (II) Halide Precursors
Chemistry of Materials
Nanocrystalline tin oxides are synthesized via precipitation from heated solutions as well as from a novel above-solution vapor deposition route that occurs at low temperatures and atmospheric pressure. Crystalline phases are characterized via powder X-ray diffraction. Samples precipitated from reactions of SnCl2 are found to exist primarily as mixtures of tetragonal SnO and tetragonal SnO2 or tetragonal SnO2 and tin(II) oxyhydroxide (Sn6O4- (OH)4), depending on reaction conditions. A mixed tin(II)/tin(IV) sample is shown to produce a rarely observed form of the intermediate oxide Sn3O4 upon annealing in air at 600 °C. SnBr2 exclusively forms tetragonal SnO2 via precipitation. Variation in the solvent composition with SnBr2 is shown to result in vapor deposition of SnO2 at temperatures below 160 °C. The average crystallite sizes of the vapor-deposited material are ≈ 3 nm and grow slowly upon heating. Partially hydrolyzed SnBr4 is proposed as the vapor deposition intermediate based on variations in precursor/solvent combinations along with FTIR and GC-MS analysis of the reaction solution removed prior to the onset of deposition.