Bong-Chull Kim

Rapid rate sintering of nanocrystalline indium tin oxide ceramics: particle size effect

The nanocrystalline indium tin oxide (ITO) powders with different particle size were prepared using a coprecipitation process and the sintering characteristics of the powders at different heating rate were examined. Decrease of particle size in nano-sized powder regime promoted the densification in normal rate sintering as temperature increased, while this retarded severely the densification at high temperature in rapid rate sintering. It is explained due to the differential densification, that is, the outmost region of the sample is well densified, while many large pores are observed inside of the densified ring. The differential densification may easily occur in the sample sintered at high temperature with small particles in rapid rate sintering, because smaller particle size has higher densification rate and higher sintering temperature in rapid rate sintering accompanies higher thermal gradient between the surface and center of a sample.

Precipitate concentration of Co2SnO4 in CoO-doped SnO2 ceramics at different oxygen chemical potentials

Abstract The precipitate concentration of Co 2 SnO 4 phase in CoO-doped SnO 2 ceramics was investigated as a function of oxygen chemical potential during heat treatment. When the SnO 2 ceramic doped with 2 mol% CoO was sintered at 1400°C for 2 h in oxygen (O 2 ) or nitrogen (N 2 ) atmosphere, a small amount of precipitated Co 2 SnO 4 phase was observed in the SnO 2 samples regardless of sintering atmosphere. When the sample sintered in N 2 was afterwards heat-treated at 1300°C for 20 min in O 2 , the amount of the Co 2 SnO 4 phase on the surface of the sample was largely increased. On the other hand, when the sample sintered in O 2 was afterwards heat-treated in N 2 , the Co 2 SnO 4 phase on the sample surface disappeared. It is suggested that outward or inward diffusion of oxygen vacancies (V O ) in the sample under different oxygen chemical potentials is coupled to outward or inward diffusion of Co-ions due to a defect association of oxygen vacancies with Co Sn ″, which causes modifications of the Co concentration at the surface and controls the precipitation fraction of Co 2 SnO 4 phase at the sample surface.

Sensing Characteristics of Cubic and Rhombohedral Nanocrystalline ITO Thick Films

Two kinds of nanocrystalline Tin doped indium oxide (or indium tin oxide: denoted ITO hereafter) powders with different crystal structures – rhombohedral and cubic – were prepared using a coprecipitation method through the control of pH of a mixing solution and aging time after coprecipitation. The two powders have the same particle size of 15 nm in diameter but different morphologies (spherical for rhomboheral and rectangular for cubic). The gaseous ethanol sensing characteristics of the sensors prepared by the two ITO powders were quite different. The sensitivity of rhombohedral ITO sensor was high compared to that of the cubic ITO sensor across all temperatures. The reason for this is explained through the viewpoint of the binding energy of XPS and the surface structure relating to the crystal structure.