Preparation Of Indium Tin Oxide (ITO) Powders And High-quality ITO Target

With the help of thermal analyses (TGA-DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersion spectra (EDS), etc., preparation of spherical or acicular indium-tin oxide (ITO) powders and preparation of ITO targets by hot isostatic pressing (HIP) were comprehensively investigated, and cylindrical ITO targets having a relative density of higher than 99% were obtained. The situations of heavy demands of ITO target and the research situations and development trends of ITO powders and ITO targets were generally reviewed. Moreover, the differences between sintering method and HIP method for preparation of ITO targets were briefly summarized, and the purposes and significances of the research works of the dissertation were indicated. Effects of technical parameters during co-precipitation processes on phase structures of ITO precursor powders were discussed, and transformation from ITO precursors to cubic ITO solid solutions were comprehensively investigated. Two kinds of ITO precursors, cubic In(OH)3 and orthorhombic InOOH, were prepared in alkali and neutral conditions respectively. Moreover, rhombohedral ITO solid solution appeared and acted as a transition phase during the transformation from InOOH to cubic ITO solid solution. Micron-scale and nano-scale acicular ITO powders were prepared in ambient atmosphere (1 atm) by concentration and co-precipitation methods respectively. The cross-sectional diameters of the most of micron-scale ITO aciculae were in the range of 2 to 9 μm, and the aspect ratios of about 95% of aciculae were more than 6, and Sn content of the surface layer was higher than that of the bulk. The cross-sectional diameters of most of ITO nano-aciculae were mainly in the range of 20 to 60nm, and the aspect ratios were mostly in the range of 4 to 12. ITO precursor nano-aciculae were composed of very subtle nano-wires of 3 to 4 nm in cross-sectional diameter, and the nano-wires were regularly arranged to be parallel to the axial direction of ITO precursor nano-aciculae. ITO nano-aciculae were composed of flaky grains whose flat surfaces were perpendicular to the axial direction. Effects of heat-treatment parameters of spherical powders, technical parameters of cold isostatic pressing (CIP) and isolated materials on HIP of ITO targets were investigated in detail, and the processes of HIP of ITO targets were simulated by computer. Single ITO solid solution having larger lattice constant than In2O3 was formed after heat-treatment of spherical ITO powders, and the tap density of the powders was promoted greatly. In-Sn alloy having a weight ratio of 97 : 3 between In and Sn was formed on surfaces of grains of reduced ITO powders, and In-Sn alloy tended to form spherical particles for the reason of not wetting ITO. Moreover, the In content of In-Sn alloy increased with the increasing of reducing degrees of ITO powders. Pressure was the key parameter of relative density of ITO green compact by CIP. ITO green compact covered with Pt foil was capsuled with 1Cr18Ni9Ti stainless steel and isolated by mixing powders of Al2O3 and Graphite or BN before HIP, and the isolation method was excellent in HIP of ITO target. The grains of ITO target was uniformly in 1 ~ 10μm in diameter, and the fracture of ITO target was absolutely along grain boundaries. The target was single ITO solid solution except that the existence of a weak diffraction peak located at 32.25°2θin XRD pattern being probably indexed to In-Sn alloy or low-valence oxides of In and Sn. The distribution of diameters of grains of HIPed ITO target using powders being not heat-treated was greatly broadened and abnormally growing grains appeared, and there existed large amount of pores in target. Moreover, the HIPed ITO target using powders being not heat-treated was ITO solid solution with precipitated SnO2 of 4.6% in weight. Author attempted to prepare small ITO targets by sintering method, and the fracture faces, phase structures and compositions of the targets were characterized. At the same time, ITO films were prepared by magnetron sputtering using HIPed targets, and effectsof relative technical parameters on phase structures, electro-conductivities, morphology and transmittance of the films were investigated. There existed a large amount of pores being 10 ~ 20μm in diameter in targets sintered in air, and Sn content and the lattice constant of ITO solid solution of targets sintered in air were smaller than targets sintered in pure O2. The ( 4 0 0 ) face of ITO films tended to grow to be parallel to the face of glasses when prepared at low O2 partial pressure, and the ( 2 2 2 ) face of ITO films tended to grow to be parallel to the face of glasses when prepared at higher O2 partial pressure. The roughness of the films tended to become smaller and the microstructures tended to become finer with the increasing of O2 partial pressure. The optical transmittance of the films tended to become higher and the electroconductivities tended to become lower with the increasing of O2 partial pressure.