World Journal of Nano Science and Engineering, 2012, 2, 6-12 Published Online March 2012 (
Morphology and Optical Measurements of Nanostructured
In2O3:SnO2 Nanoparticle
A. Ayeshamariam1*, M. Jayachandran2, C. Sanjeeviraja3, M. Tajun Meera Begam4
1Department of Physics, Khadir Mohideen College, Adirampattinam, India
2ECMS Division, CECRI, Karaikudi, India
3School of Physics, Alagappa University, Karaikudi, India
4Department of Chemistry, Avvaiyar Government College for Women, Karaikal, India
Email: *
Received May 18, 2011; revised June 17, 2011; accepted October 20, 2011
Ultra-fine and uniform ITO nanopowders can be prepared by very simple Combustion method. In this paper, effects of
Indium oxide with Sn doping on crystallinity, band gap values by UV studies and morphological studies by SEM and
TEM analysis of nanopowders are reported. Powder mixtures of In2O3:SnO2 of 90:10 compositions are prepared and
calculated grain size from X-ray diffraction measurements. The free electron absorption is determined from spectral
transmission and reflection measurements. Key words: In2O3:SnO2, XRD, UV, Combustion and SEM.
Keywords: In2O3:SnO2; XRD; UV; Combustion; SEM
1. Introduction
In2O3:SnO2 (also called indium tin oxide or ITO) is a
highly degenerate n-type wide gap semiconductor that is
produced by doping Sn atoms in In2O3. Since ITO pow-
ders have a high transmittance in the visible range and a
high conductivity simultaneously, they are widely used in
a variety of electronic and optoelectronic fields. In Com-
bustion process In2O3:SnO2 powders show an interest-
ing and technologically important combination of prop-
erties: they have luminous transmittance, high infrared
reflectance, good electrical conductivity, excellent sub-
strate adherence, hardness, and chemical inertness. Com-
posite powders have been patented for use as agrochemi-
cals and herbicides. Parent et al. [1] used extended X-ray
absorption fine structure (EXAFS) investigations and
found that the In atomic environment was modified by
the Sn doping. Even at low tin concentrations the first
oxygen polyhedron and the metallic In-In co-ordination
shells were disordered. This disorder increases with the
amount of tin inserted. Tin doped indium oxide is exten-
sively studied as a base material for its gas sensor appli-
cations. It is oxygen deficient and therefore is an n type
semiconductor with a wide band gap (3.53 eV) [2]. The
effect of crystallite size on the optical prop erties has been
widely studied [3]. Nanocrystalline powders have at-
tracted considerable interest because of their high trans-
mittance. Here, we have presented the optical properties
of 90:10 nanocrystalline ITO powders [4 ].
1.1. Physical Characterization
The visible transmission was recorded using Hitachi
S3400N Spectrophotometer. The calcined powders were
further characterized by particle size analysis (Autosizer
IIC Malvern) and powder X-ray diffraction (XRD) (X-
ray diffractometer (XRD) with monochromation CuKα
target (1.5406 Å) at a scan rate of 2˚C/min). Unit cell pa-
rameter was calculated from the observed “d”-spacing,
which was accurately measured with the help of silicon
as an internal standard. Particle size and morphology of
the synthesized powders were further evaluated with the
help of a transmission electron microscope TEM (JEOL
JEM 200CX). Scanning electron microscope (SEM) and
Energy dispersive X-ray analysis (EDAX) work on the
calcined powders were performed under Scanning Elec-
tron Microscope Cambridge 53400N and elemental analy-
sis was studied by EDAX Make “thermo software Nor-
ton systems”. The asprepared powders were pelletised at
a pressure of 500 kg/m2.
1.2. Experimental
The Combustion method is a useful technique that has been
shown to be good preparation route for ITO nanopowders
[5]. It is based on exothermic and usually very rapid
chemical reaction between metal nitrates as an oxidizer
and an organic fuel [6], such as Urea, glycine and so on.
*Corresponding author.
opyright © 2012 SciRes. WJNSE
A key feature of the method is that heat is required to
maintain the chemical reaction supplied from the reaction
itself that is not from an external source but from an in-
ternal one. Therefore to achieve an optimized combus-
tion reaction condition, many chemical reaction parame-
ters must be considered [7]. Among known fuels we used
the urea which had the versatility of combustion synthe-
sis methods by showing successful preparation of a large
number of well crystallized multicomponent oxides [8].
The raw materials used in this study are In(NO3)2·2H2O,
Sn(NO3)2·3H2O, these raw materials were dissolved in
distilled water and mixed in a appropriate ratio to form a
tin nitrate solution. Then urea (CO(NH2)2) was added to
this solution. The amount of urea was fixed at 1.0 mol [9].
Amount of urea was calculated based on total valence of
the oxidizing and reducing agents for maximum release of
energy during combustion. Oxidant/fuel ratio of the sys-
tem was adjusted by adding nitric acid and ammonium
hydroxide; and the ratio was kept at unity. The solution was
heated under constant stirring at a temperature of about
60˚C in a Pyrex vessel on a hot plate. Then the concentra-
tion of the solution slowly became higher. The resulting
translucent solution was heated on a hot plate (at about
100˚C) until it turned into a viscous solution. The solu-
tion boils upon heating and undergoes dehydration ac-
companied by foam. The foam then ignites by itself due
to persistent heating giving a voluminous and fluffy pro-
duct of combustion. The combustion product was subse-
quently characterized as single phase nanocrystals of ITO.
The resulting ashes were then fired at a temperature
higher than 350˚C until complete decomposition of the
residues was achieved. Yellow ashes obtained after com-
bustion were then collected for structural characterization
and other morphological studies. The system was homo-
geneous during the whole process and no precipitation
was observed. The entire processing steps are illustrated
in Figure 1. The final mixtures are heated for two dif-
ferent temperatures of 300˚C and 500˚C.
2. Results and Discussion
2.1. XRD
Structural studies by XRD showed the presence of domi-
nant β-phase with a minor quantity of α-phase. The atomic
arrangements in the grain boundary seem to be somewhat
different from regular periodic arrangement whereas in-
side the grain there is a good periodic arrangement of at-
oms. Figure 2(a) shows the XRD structure of different
temperature. XRD lines are indicating that Sn has gone to
the substitutional position forming solid solution. XRD
shows complete oxidation of the alloy giving mainly
cubic phase of In2O3. The crystallite size of the nano-
crystalline powder is estimated using Scherer formula
[10]. Average value of grain size varies from 9 nm to 18
Figure 1. (a) Schematic representation of precursor sol
preparation and ultra fine powder by Combustion synthesis;
(b) XRD of proportions (90:10).
nm for the prominen t o f p eak ( 222) (400 ), (4 40) and (622 )
orientation. Fro m the figures the analysis of crystal struc-
Copyright © 2012 SciRes. WJNSE
Copyright © 2012 SciRes. WJNSE
he solu-
tend mainly to gather near the Sn ion on In2 sites and can
form strongly bound O-Sn-O units. This occupation me-
chanism does not produce additional free electrons. The
increase in conductivity is only small. Larger doping
concentrations cause a further oxygen reception. Apart
from the O-Sn2-O units O-Sn1-O arrangements can also
occur. This effects a further distortion of the bix-byte
structure. The microstrain increases and the domain size
decreases which is shown in Figures 2(b)-(d). The grain
size strain values are shown in Table 1.
ture revealed that the detected peak of the nanoparticle
was corresponded with that of crystallized ITO. That is
very intense peak was found at the three most important
peaks of In2O3 namely (222 ), (400) and (440) r eflections.
The diffraction patterns are well matched with TEM resu lts
shown in Figure 3. EDAX analysis confirmed the prepared
nanoparticles were fine indium tin oxide powdered and
there was no impurity in it as shown in Figure 5.
ITO materials retain the cubic structure upto t
lity limit of the SnO2 in In2O3 [11] at 90:10 doping con-
centrations when the temperature increases the lattice
constant also increases rapidly. Then the tin ions occupy
In1 and In2 sites shown in Figure 1(b). The stoichiomet-
ric balance can be maintained only if additional oxygen
is inserted into the lattice. These oxygen atoms can fill
the empty tetracheal sites in the bixbyite structure. They
2.2. UV Studies
It was reported that, the model developed by Franck and
Kostlin [12] for tin insertion into In2O3 results from an
analysis of the carrier concentration and additional meas-
urements of the lattice constants dependent on the doping
0 102030405060708090
Relative Intensity (A.U)
2 Theta
As prepared
As Prepared300500
Grain Size (nm)
(a) (b)
As Prepared300500
Lattice Constant (A0)
As Prepared300500
2 x 10-3
3 x 10-3
4 x 10-3
(c) (d)
Figure 2. (a) XRD analysis fo(d) Micro strain.
r two di fferent temperatures; (b) Grain Size; (c) Lattice Constant;
Figure 3. SAED for as prepared sample.
Sample Micro strain
Table 1. XRD results of ITO.
(ITO) Grain Size Lattice Constant
(nm) (Å) lines/m
As Prepared 8.776 10.124 4 × 10–3
300˚C 11.142 10.126 3 × 10–3
500˚C 17.217 10.138 2 × 10–3
oncentration. Optical analysis comprises two kinds of c
interstitial oxygen, one of which is loosely bound to tin,
while the other forms a strongly bound Sn2O4 complex.
At low doping concentration (10% Sn) here we found de-
creasing lattice constants and therefore concluded a domi-
nance of the loosely bound tin-oxygen defects. Optical
absorbance and transmission (T) spectra Figures 6(a)-(c)
were measured using a near-infrared to UV double-beam
spectrometer. Optical absorption coefficients (α) were cal-
culated by correcting the reflection using a formula α =
kh Eh
, where Eg is the optical band gap
(Tauc ns a constant. Using the model with n =
2 proposed by Tauc, Eg was estimated by linearly ex-
trapolating the plot of
gap) and i
vs hv and finding the in-
tersection with the abscissa auc Plot) [13,14] shown in
Figures 7(a)-(c) and 8. The band gap for different tem-
peratures are shown in Table 2.
2.3. SEM Analysis
90:10) leading to an interconnected
SEM photograph ITO (
spherical structure with good mechanical strength. The
nano-structural changes taking place during combustion
process leads to a decrease in pore size and pore diameter.
The nano-structural changes are accompanied by the as-
sociated internal stresses in the membrane. Increasing the
annealing temperature with respect time can lead to local
shifts in the interconnected grains, so as to reduce the
internal stresses. It is well documented that the surface
of nanostructure materials. The reaction temperature is one
among them. We obtained surface spherical morphologies
of ITO asprepared, 300˚C and 500˚C using ITO powder as
source material. Figures 4(a)-(c) show Scanning Electron
Microscopy (SEM) images of spherical-shaped ITO nano-
structures at (100˚C, 300˚C and 500˚C) different tem-
peratures [15].
morphology has a significant impact on the perform
Figure 4. (a) SEM for asprepared sample; (b) SEM analysis
at 300˚C; (c) SEM analysis at 500˚C.
Copyright © 2012 SciRes. WJNSE
Figure 5. EDAX.
050010001500 2000 2500
Asp 90% 10%
% of Transmis sion
Wavelength (nm)
05001000 1500 2000 2500
300 ITO 90% 10%
% of Transmi s sion
Wavelength (nm)
05001000 1500 2000 2500
500 ITO 90% 10%
% of Transmission
W av elength (nm)
Figure 6. Transmittance cu of (a) ASP; (b) 300˚C; (c
rves )
(b) (b)
Copyright © 2012 SciRes. WJNSE
Figure 7. Band gap values of (a) ASP; (b) 300˚C; (c) 500˚C.
Figure 8. Grain size and bandgap values of ITO.
Table 2. Bandgap values of ITO.
Sample (ITO) Bandgap (eV)
As prepared 3.197
300˚C 3.156
500˚C 3.135
2.4. Sensor Analysis
The addition of a small amount of doping elements to
SnO2 powders has been known to be effective in modi-
fying their optical and electrical properties [16]. In par-
ticular, in the case of gas sensor applications, a gene
strategy for tailoring matee selective sensor
ddition of dopan ts during sen sor fabrication [17]. Hen ce,
there is a growing interest in doping SnO2 with different
rials for th
response involves the modification of the surface by the
0150 300 450 600 750 900
In2O3 90% SnO2 10%
Time (Sec)
igure 9. Sensitivity with respect to time of as prepared sam-
elementent study, we oease in
grain sizrease in temperatur
of the sampepared is of the ordernm. In this
works, graieffects on the sensitivgas sensor
devices have reported shown in Figure 9.
But the powders are highly resistive. Hence, In2O3:SnO2
dopings can be used in areas where only a moderate elec-
tronic conductivity is required.
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