K. Yanagisawa et al.: Preparation and characterization of fine indium tin oxide powders
spectively. Then the solution was added drop-wise
analyzed by a least square fit to the Lorentz function.
Thermogravimetric differential thermal analysis (TG-
DTA; SEIKO-SSC-5200H, Seiko Instruments Inc., To-
kyo, Japan) of the hydrothermally treated powder was
carried out from 25 to 1000 °C in air in order to study the
precursor decomposition and the phase changes. The test
cell contained 10 mg of sample, while the standard cell
contained 10 mg of ␣–Al2O3. The heating rate was
20 °C/min. Morphological characterization of the pre-
pared powders was performed using transmission elec-
tron microscopy (TEM; Hitachi H-800, Tokyo, Japan) at
200 kV. The samples were supported on carbon-coated
100 mesh copper grids. A portion of each powder was
dissolved in 1 M HCl and analyzed by inductively
coupled plasma atomic emission spectrometer (ICPS-
SPS 7000A-SII Seiko Instruments Inc., Tokyo, Japan).
(2 ml/min) to 5 M NH4OH (500 ml, excess) solution
(Wako Pure Chemical Industries, Ltd., Osaka, Japan)
while stirring. A light yellow color gel precipitate was
obtained. The reaction mixture soaked at 80 °C for 10 h
while stirring. The precipitate was then filtered and thor-
oughly washed with distilled water until it was free from
Cl− and NH4 . The co-precipitated gel was air-dried. The
+
gel was next hydrothermally treated at 300°C for 24 h
using a microautoclave (inner volume 20 cm3), with a
Hastelloy C corrosion resisted linear. The fill ratio of the
solution volume against the inner volume of the auto-
clave was 60%. The pH of the media was controlled
using ammonia solution. After the hydrothermal treat-
ments the powders were filtered and washed with dis-
tilled water, then dried at 50 °C under vacuum. The
powder was calcined at 500–1000 °C for 4 h in air in
order to obtain the ITO powder. X-ray diffraction (XRD)
measurements (Rigaku, Rotaflex, Tokyo, Japan) of the
coprecipitated gel and its hydrothermal and calcined
products were carried out for phase identification. The
lattice parameters of both the hydrothermally treated Sn
doped and undoped samples were obtained by XRD. Na-
tional Bureau of Standards (NBS)–Si powder was used
as an internal standard for calibration. The powder dif-
fraction patterns of from 2 ס
20° to 70° were recorded
with a scan speed of 0.01° 2/min. The unit cell param-
eters observed were subjected to a least-square refine-
ment. The 119Sn Mo¨ssbauer spectra (Wissel GmbH,
Germany, used inconstant acceleration mode) of hydro-
thermally produced and calcined powders (700 °C for
4 h) were performed at room temperature in order to
study the environment of tin in the ITO powders. 119Sn in
CdSnO3 was used as a ␥-ray source and the specimen
powder was used as an absorber. Mo¨ssbauer spectra were
measured by transmission geometry. The relative veloc-
ity between the source and absorber was calibrated using
the ␣–Fe spectrum of 57Fe at room temperature. The
isomer shift is relative to BaSnO3. Spectra obtained were
III. RESULTS AND DISCUSSION
Separate coprecipitation experiments showed that pre-
cipitation of In(OH)3 and Sn(OH)2 occurs above the pH
values of 5 and 2.2, respectively. During aging in an
aqueous media, In3+ and Sn2+ cations combined with
OH− to form In(OH)3 and Sn(OH)2 and formed hydrous
gel type precipitates. Therefore, a homogenous gel is
formed the coprecipitation method. The coprecipitated
gel particles show very poor crystallinity as shown in
the XRD pattern in Fig. 1(a). The XRD pattern shows
broad low intensity peaks that were also observed in the
pure In(OH)3 gel. The evolution in the intrinsic micro-
structure of the gel powder was studied TEM. Observa-
tions show [see Fig. 2(a)] highly aggregated particles
approximately 15 nm in size. The absence of well-
defined rings in the electron diffraction pattern (not
shown in the figure) confirms that the particles are sub-
stantially amorphous.
Under hydrothermal conditions the reactant was con-
verted to a well-crystallized powder. The XRD pattern of
the hydrothermally treated powder is shown in Fig. 1(b).
The narrow peaks of the XRD pattern indicate that the
treated powder has well-crystallized fine particles. The
powder was identified as single-phase tin-doped indium
oxyhydroxide with lattice parameters a ס
5.2561 ±
0001 Å, b ס
4.5788 ± 0001 Å, and c ס
3.2702 ±
0001 Å, (cell volume 78.70 ± 0.01 Å3) the crystal struc-
ture is a long range ordered orthorhombic system similar
to InOOH.9 No additional phases are observed. A similar
phase of InOOH was observed10 under hydrothermal
conditions at 300–400 °C with very high pressures
(>80 atm) and long treatment times (100 h) with the lat-
tice parameters of a ס
5.26 ± 0.01 Å, b ס
4.56 ±
0.01 Å, and c ס
3.27 ± 0.01 Å. The lattice parameters of
pure InOOH phase in this study were determined as a ס
5.2698 ± 0.0001 A, b ס
4.5702 ± 0.0001 Å, and c ס
3.2755 ± 0.0001 Å (cell volume 78.70 ± 0.01 Å3), re-
FIG. 1. XRD patterns of (a) the In–Sn coprecipitated gel powder (b)
after hydrothermal treatment at 300 °C for 24 h and after calcination in
air for 2 h at (c) 500 °C, and (d) 700 °C.
J. Mater. Res., Vol. 15, No. 6, Jun 2000
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