Synthesis of Cubic and Rhombohedral Phased Nanocrystalline SnO 2 Doped In 2 O 3 [ITO] Powders with Coprecipitation Metho
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Among these powder processing techniques, coprecipitation
has been
suggested as a simple and economic way to obtain nanocrystalline ITO powders with good controlled particle size and morphology. In the coprecipitation method, the morphology, particle size, and composition of precipitates depend on several parameters such as aging, concentration, temperature, pH, and the kinds of anions present[8-10]. In the present work, the morphology and the structure of the precipitate were controlled by varying aging time. As a result, cubic and rhombohedral nanocrystalline ITO powders were produced, and the fraction of the phases was dependent on the aging time. Therefore, selective production of nanocrystalline ITO powders with cubic or rhombohedral structure was available. EXPERIMENT Indium nitrate hydrate [ln(NO0)4 xH 2 ]Oj and tin chloride hydrate(SnC14xH 20) were used as starting materials. Mixed solutions of indium and tin were prepared by dissolving indium nitrate hydrate and tin chloride hydrate in doubly deionized water, respectively. Concentration and In/Sn atomic ratio in mixed solution were fixed to I N and 92/8, respectively. NH 4OH was added directly to a continuously stirred mixed solution until the pH reaches to 8.5. Then precipitate in Pyrex glass was sealed with silicon cover and aged for 0, 12, 24, and 48h After the aging process, precipitates were washed several times with deionized water using ultrasonic equipment and dried at 85'C. The dried precipitates were calcined at 600'C for I h in air and nanocrystalline ITO powders were produced. In/Sn atomic ratios in the nanocrytalline ITO 27 Mat. Res. Soc. Symp. Proc. Vol. 581 © 2000 Materials Research Society
powders were confirmed as 92/8 by a X-ray fluorescence spectrometer (XRF; Model PW 2400, Philips). .0 0 0 -" 0 •0 0'' 10 Phase identification and particle size measurement were performed by a 100 X-ray diffractometer of the powders 8 (XRD; Mac Science) using CuK,, 6 radiation. Fractions of cubic and X C. rhombohedral phases in calcined 4 .0 nanocrystalline ITO powders were obtained by calculating integrated 2 0 2 intensities of the (110) peak of 0 0 rhombohedral ITO (JCPDS No. 210406) and the (222) peak of cubic ITO 4 6 8 0 2 (JCPDS No. 44-1087) after being [OH]/[In+Sn] Ratio subtracted Ka2 and split multi-peak by using a software. The particle size of Fig. 1. NH OH titration of [Sn+ln] solution at 4 the powder was calculated from X-ray 15'C and concentration of I N. peak broadening using the Scherrer equation[I 1]. Si standard powders were used as a reference. The morphology and size of precipitates and ITO powders were examined by a transmission electron microscopy (TEM; Model H-7100, Hitachi). In addition, the dried precipitates were characterized by Fourier transform infrared (FT-IR) spectroscopy (Model IFS I20HR, Bruker).
0m
•
lOOnm
100nrnm
.. -
....
. .
Fig.2. TEM images of the precipitates with aging time of(a) 0, (b) 12, (c) 24, and (d) 48 h.
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RESULTS and DISCUSSION Figure 1 shows the change of pH value of the mixed solution with
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