The effect of Sn(IV) on transformation of co-precipitated hydrated In(III) and Sn(IV) hydroxides to indium tin oxide (ITO) powder

Multicomponent metal oxide (indium tin oxide, ITO) powders were prepared by the hydrolysis of their corresponding metal salts following co-precipitation technique. Indium tin oxide powders with relatively high content of tin were prepared by the treatment of aqueous NH4OH with the mixture of aqueous In(NO3)3 and SnCl4 solution (pH=8.4–8.7) at an ambient temperature. The composition of the powders were 90:10, 70:30 and 50:50 (In/Sn atomic ratio). The air-dried powders were cured at different temperatures and also at different atmospheric conditions [air and H2(5%)–Ar(95%)]. They were characterized by FTIR spectroscopy, thermal analysis and X-ray powder diffraction studies. FTIR spectroscopy and thermal analysis of powders revealed that the air-dried powders existed as hydroxides of In3+ and Sn4+ in the solid state which transformed to ITO via some metastable intermediates after 300 °C. In addition, the formation of InOIn and SnOSn type of bonding was also predicted by FTIR. Below 200 °C, the powders predominantly existed as corresponding hydrated oxide phases which corresponded to possible formulations, In(OH)3 and SnO3H2 and transformed to ITO phases after 300 °C. The powders containing below 30% Sn showed pure cubic In2O3 phase whereas the casseterite structure of SnO2 phase was observed in the case of relatively high Sn content (Sn>30%). The crystallite size of the powders increased with temperature as well as with increase in Sn content.