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

Abstract

Nanocrystalline indium tin oxide (ITO) powders with different tin contents ranging from 0 to 8 at% were prepared by a coprecipitation process. A mixture of rhombohedral and cubic structured nanocrystalline ITO powders was obtained, and the amount of the rhombohedral ITO increased as the content of Sn increased. During heat-treatment the rhombohedral ITO was transformed to cubic around 900 • C. The phase transformation behavior of the powders was examined as a function of oxygen partial pressure. When the rhombohedral ITO powder was heat-treated in a low oxygen partial pressure (nitrogen gas) atmosphere the phase transformation was accelerated and this acceleration can be attributed to the formation of oxygen vacancies that accelerate atomic transport in the rhombohedral ITO.

Solid state sintering of nano-crystalline indium tin oxide

“…lower than 1200 • C, which has received very little attention in the literature, is also emphasized. The present findings are compared to corresponding studies of nano-crystalline powders prepared by co-precipitation 14,15,17,18,20 or mixtures of nano-crystalline In 2 O 3 and SnO 2 . 19 Finally, the importance of ball-milling to remove agglomerates in nano-crystalline materials is illustrated.…”

“…The phase purity was particularly important with respect to previous studies of nano-crystalline ITO materials. [14][15][16][17][18][19][20][21] The crystallite sizes of the In 2 O 3 and the ITO powders, calculated by the Scherrer equation, was found to be 26 ± 1 nm and 16 ± 2 nm respectively. The BET surface areas of the powders were 24.9 ± 0.8 and 39.4 ± 1.3 m 2 /g, giving an average particle size of 34 ± 1 nm for In 2 O 3 and 21 ± 1 nm for ITO.…”

“…It has been noted in several reports that it is advantageous to sinter ITO in oxygen. [13][14][15]20 The difference in sintering behaviour in synthetic air and oxygen was minor, while there was a significant difference between the two oxygen-rich atmospheres and nitrogen (with an estimated oxygen partial pressure of 10 −4 -10 −5 ). Below approximately 900 • C the sintering kinetics is not influenced by the atmosphere.…”

“…[14][15][16][17][18][19][20][21][22] In most of these studies nano-crystalline In 2 O 3 and ITO was prepared by co-precipitation methods. [14][15][16][17][18]20,21 Single phase SnO 2 -doped In 2 O 3 can however not be prepared by co-precipitation due to simultaneous precipitation of both In and Sn hydroxides, resulting in heterogeneous cation distribution. 17,21 Recently we have developed an aqueous sol-gel route to synthesize single phase nano-crystalline ITO powders, 23 which overcome the problems related to the co-precipitation route.…”