Effect of Phase Transformation on the Densification of Coprecipitated Nanocrystalline Indium Tin Oxide Powders

Abstract

Two kinds of nanocrystalline indium tin oxide (ITO) powders with different crystal structures—rhombohedral and cubic—were prepared using a coprecipitation process through the control of aging time of precipitates after coprecipitation. The densification characteristics of the two ITO powders were examined. During sintering the rhombohedral ITO, which is a high‐pressure phase, was transformed to cubic around 900°C. The phase transformation induced coarsening of grains and many voids in the microstructure retarded densification. On the other hand the cubic ITO, which did not experience phase transformation during sintering, was well densified as the sintering temperature increased. Poor densification of the rhombohedral ITO powder is explained from the viewpoint of coarsening of grains during the phase transformation. This result shows the significance of phase transformation during sintering.

Modified Pechini Synthesis of Oxide Powders and Thin Films

“…In most of these studies, nano-crystalline In2O3 and ITO were prepared by co-precipitation (Kim et al 2002;Kim et al 2006), although a few reports with modified Pechini-methods exist (Sunde et al 2012). The modified Pechini methods avoid the simultaneous precipitation of both indium and tin hydroxides, which ruins the homogeneity on the atomic scale using coprecipitation.…”

Phase Transformation Behavior of Nanocrystalline ITO Powders during Heat-Treatment: Oxygen Partial Pressure Effect

“…In this case, because long-range diffusion is kinetically limited during crystallization, metastable phases often crystallize depending on the precursors [2][3][4]. Otherwise, the extremely small curvature radius of nano particles induces high capillary force on the particles, which often forms high-pressure phases in nano powders [4]. When the metastable and/or high-pressure phases are exposed to higher temperatures, phase transformations to the stable phases have been observed [2][3][4].…”

“…During nano powder fabrication processes in chemical routes precursors are usually pyrolyzed to an inorganic material at as low a temperature as possible to form a crystallization in order to prevent particle coarsening. In this case, because long-range diffusion is kinetically limited during crystallization, metastable phases often crystallize depending on the precursors [2][3][4]. Otherwise, the extremely small curvature radius of nano particles induces high capillary force on the particles, which often forms high-pressure phases in nano powders [4].…”

Sintering of Transparent Conductive Oxides: From Oxide Ceramic Powders to Advanced Optoelectronic Materials

“…The sintering of cubic and rhomboedric nanosized ITO powders with mean particle sizes in the range of 50 to 100 nm were sintered up to 900 °C (Kim, et al, 2002) where the cubic phase was transformed. This transformation should theoretically results in a volume expansion of 2.1 % which was not observed since grain growth and pore formation were initiated.…”

“…The phase transformation promoted the active diffusion of atoms resulting in inhomogeneous grain growth with intragranular pore formation. It is therefore recommended to prevent phase transformation during sintering in order to achieve higher densification rates and more homogeneous microstructures (Kim, et al, 2002).…”