International Journal of Electronics and Computer Science Engineering
Available Online at www.ijecse.org
1422
ISSN- 2277-1956
Synthesis and Characterization of Tin Oxide as
Humidity Sensor
Ritesh Kumar1 , Indu Verma2, Nidhi Verma3
Department of Physics, University of Lucknow,
Lucknow-226007, India
Email- 1 riteshnanodu11@gmail.com
1, 2,3
Abstract- The bulk SnO2 was synthesized by oxidizing the fine powder (50 mesh) of metallic tin (purity 99.99, Aldrich)
powder at 750°C for 9 hrs hours in programmable temperature controlled furnace. The gross structure and phase purity
of the powder sample ground from sintered pellets were examined by powder X-ray diffraction technique. The phase
identification /gross structural characteristics of synthesized SnO2 materials explored through powder X-ray diffracto
meter reveals that the sample crystallize in tetragonal structure with lattice parameters a = b = 4.7346Å, c = 3.1787Å. The
surface morphology investigated through scanning electron microscope and atomic force microscopy (SEM & AFM)
results that pure SnO2 possesses uniform grains and is almost homogeneously distributed, which indicates the high
packing density of the materials and nano spheres like structures on the surface of SnO2sample. Average sensitivity of the
sensor was found to be 27 MΩ/%RH.
Keywords – SnO2, SEM, AFM and average sensitivity.
1. INTRODUCTION
Among these oxides, Tin oxide (SnO2) belongs to a class of materials that combines high electrical conductivity
with optical transparency and thus constitutes an important component for optoelectronic (photovoltaics)
applications, rechargeable lithium batteries [1], antistatic coating, and transparent electrode preparation and widely
used as a photo catalyst for oxidation of organic compounds. Tin oxide is an n- type wide band gap semiconductor
(Eg = 3.6 ~3.97eV)and its electrical properties critically depend on its stoichiometry with respect to oxygen, on the
nature and amount of impurities or dopants present and on its size as well as shape of nanostructures [2-4].
Materials based on tin oxide (SnO2) have also been proposed as alternative anode materials with high energy
densities and stable capacity relation in lithium -ion batteries [5-8]. Tin oxide has also been one of the first
considered and still has shown very high sensitivity towards reducing gases such as H 2, CO, hydrocarbon, and
alcohol. Its sensitivity can be further improved by increasing the surface area. Therefore the use of porous nano
structured SnO2 with large surface to volume ratio and small crystal size could lead to easy gas transport and
interesting optical and electrical properties [9-15].
Stannic oxide is formed in the structure of rutile, the spatial group being P4/mnm. The unit cell is
tetragonal, it consists of six atoms – two stannum and four oxygen atoms – and is characterized by the lattice
parameters a and cand intrinsic parameter u. The atoms of Sn are located in the bcc-positions (0, 0, 0) and (1/2, 1/2,
1/2) and are surrounded by oxygen atoms being in the positions ± (u, u, 0) and ± (1/2+u, 1/2–u, 1/2) to form a
distorted tetrahedron. The optimized cell parameters obtained in the calculation are as follows: a=b= 4.738Å, c=
3.188Å and u = 0.30756. In the bulk all Sn atoms are six fold coordinated to threefold coordinate oxygen atoms.
SnO2 is an anisotropic polar crystal, [16-20] which crystallizes in tetragonal rutile structure with spacegroup D4h
[P42/mm] [21, 26]. The unit cell contains 6 atoms, 2 tins and 4 oxygen. Each tin atomis at the center of six oxygen
atoms placed approximately at the corners of a regular slightly deformed octahedron, and three tin atoms
approximately at the corners of an equilateral triangle surround every oxygen atom.
2. EXPERIMENTAL DETAILS
In the present investigation firstly the bulk SnO 2 was synthesized by oxidizing the fine powder (50 mesh) of metallic
tin (purity 99.99, Aldrich) powder at 750°C for 9 hrs hours in programmable temperature controlled furnace. In
second step the as synthesized SnO2 powder was palletized in a hydraulic press machine at the pressure of 300-400
ISSN 2277-1956/V1N3-1422-1426
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Synthesis and Characterization of Tin Oxide as Humidity Sensor
Kg/cm2.The resulting pellets of undoped SnO2 of 10mm diameter and 2 mm thickness were sintered at 900 0C in air
for 9 hours in a programmable SiC furnace.The gross structure and phase analysis of the samples at different stages
of calcinations were carried out by powder X-ray diffractometer (18KW rotating anode Cu target, Rigaku, Japan).
The surface morphology of the as partially melted pellets were carried out through Joel scanning electron
microscopy (SEM, JSM-5600) and Nanoscope-E digital Instruments atomic force microscope (AFM).
3. RESULT AND DISCUSSION
The gross structure and phase purity of the powder sample ground from sintered pellets were examined by powder
X-ray diffraction technique. We have also calculated the lattice parameters using high angle XRD lines such as
(002), (310), (112), (301) and (202) shown in figure 1. The calculated lattice parameters of the tetragonal unit cell
has been observed a=b= 4.7346Å, c= 3.1787Å.The diffraction peaks are markedly broadened, which indicates that
the crystalline sizes of samples are small. According to the Debye-Scherer’s equation:
dRX = k.λ / βCosθ
(1)
Where λ is the X-ray wavelength (1.5418Å for CuKα), θ is the Bragg angle and β is the full width of the diffraction
line at half its maximum intensity (FWHM). The crystallite sizes were calculated to be ~ 62, 53, 75 nm for the
undoped tin oxide sample corresponding to the diffraction peaks 110, 101 and 211 respectively.
Fig. 1 XRD of SnO2 sample.
The scanning electron microscopic (SEM) technique is powerful methods for providing the information about the
surface morphology (e.g. porosity, cracks, size and orientation of grains etc.) of as synthesized materials in different
regions respectively, so the scanning electron microscope operating at voltage 20 KV with resolution limit 3.5 nm
(Jeol- JSM 5600, at CSR, Indore) is again employed for the surface characterization.
Fig. 2 SEM image of SnO2 sample.
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IJECSE,Volume1,Number 3
Ritesh Kumar et al.
The surface morphology of randomly aligned pure SnO 2 nano spheres with diameter of 15-190 nm of pure is shown
in fig. 2. The SEM pictures clearly show that pure SnO2 possesses uniform grains and is almost homogeneously
distributed, which indicates the high packing density of the materials. Also AFM is the basic confirmation tool and it
plays an important role in nanotechnology. The surfaces of as partially melt and sintered pellets were analyzed using
a Nano scope-III atomic force microscope with Scanning Tunneling Microscope (STM) attachment.AFM in contact
imaging mode in the air was used to obtain topographic images. To locate the oxide scale over well-separated two
phases, initial 40 µm x 40 µm scans were made on the specimen surface. The 2-dimensional AFM images appear as
a nano sphere like structures on the surface as shown in figure 3. In order to check the difference in thickness
profiles, line scans were also carried out across the oxides scales formed on the both phases. The most pronounced
difference in the two layers of oxide is around 35 nm. It is noted that fluctuation in the scan profile in the upper layer
as well as in the lower layer is due to changes from one grain to another grain of the oxides. Figure 4 shows the
three- dimensional (3D) view of the same surface. The formation of the humps in some places could be clearly seen,
which is due to formation of oxide layer with different thickness depending on the chemical composition of phases.
Fig. 3 Two dimensional AFM image of SnO2 sample.
Fig. 4 Three dimensional AFM image of SnO 2 sample.
This principle is employed for the measurement of moisture in resistive type humidity sensor.
S
ΔR
M /RH%
ΔRH%
(2)
The sensitivity of sensor at different annealing temperatures has been calculated. Sensitivity of humidity sensor has
been defined as the change in resistance (ΔR) of sensing element per unit change in relative humidity (%RH).The
change in impedance of porous ceramics at different environmental humidity values is related to the water
adsorption mechanism on the oxide surface.
The sensing element prepared at temperature 900°C show that as % RH increases from 25-95 % the
resistance decreases markedly and gave maximum average value of sensitivity in this region which was 27
M/%RH.
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Synthesis and Characterization of Tin Oxide as Humidity Sensor
Fig. 5: Variation in resistance in M against %RH.
4. CONCLUSION
The calculated lattice parameters of the tetragonal unit cell has been observed a = b = 4.7346Å, c = 3.1787Å. The
surface morphology of randomly aligned pure SnO 2 shows nano spheres with diameter of 15-190 nm. The SEM
pictures clearly show that pure SnO2 possesses uniform grains and is almost homogeneously distributed, which
indicates the high packing density of the materials. The sensing element prepared at temperature 900°C show that as
%RH increases from 25-95 % the resistance decreases markedly and gave maximum average value of sensitivity in
this region which was 27 M/%RH.
5- ACKNOWLEDGEMENT
We are grateful to Prof. C. D. Dwivedi of Department of Physics, D.M.S.R.D. E., Kanpur, India and Dr. P.
K. Khanna of Department of physics, C-MET, Pune, India.
6. REFERENCES
[1] Q. Kuang, C.Lao, J. L. Wang, Z. Xie, Zheng, “Nanostructure characterization and performance evaluation of ” J.
Am. Chem. Soc,.129, pp. 6070-6071, 2007.
[2] C.A. Ibarguen, A. Mosquera, R. Parra, M.S. Castro, “Synthesis of Tin Oxide (SnO2) by the Oxalate Route:
Effects of ...” J.E. Rodriguez-Paez, Mater. Chem. Phys. 101, pp. 433-440, 2007.
[3] J. S. Lee, S. K. Sim, B. M., K. Cho, S. W. Kim, and S. Kim, “Surface characterization and functionalization of
carbon nanofibers” J. Cryst. Growth. 267, pp. 145-147, 2004.
[4] G. Ansari, P. Boroojerdian, S. R. Sainkar, R. N. Karekar, R. C. Alyar, and S.K. Kulkarni, “High-performance
temperature-selective SnO2:Cu-based sensor” Thin Solid Films. 295,pp. 271-276, 1997.
[5] Y. S. He, J. C. Campbell, R. C. Murphy, M. F.Arendt and J. S. Swinnea, “Structural, electrical, and optical
properties of SnO2 nanocrystalline ...” J. Mater. Res. 8, pp. 3131-3134, 1993.
[6] Y. Idota, T. Kubota, A. Matsufuji, Y. Maekawa, T. Miyasaka, “Structural Investigation of Tin Oxide Glasses C.
Gejke, A. Matic, and ...” Science. 276, pp. 1395-1397, 1997.
[7] J. O. Besenhard, J. Yang, M. Winter, “Improvement in electrochemical properties of nano-tin-polyaniline ...” J.
Power Sources. 90, pp. 70-72, 2000.
ISSN 2277-1956/V1N3-1422-1426
IJECSE,Volume1,Number 3
Ritesh Kumar et al.
[8] I. A. Courtney, J. R. Dahn, “Optical Reflectance of Pure and Doped Tin Oxide: From Thin Films ......” J
Elertcochem. Soc. 144, pp. 2045-2048, 1997.
[9] M. Kojima, H. Kato, M. GAtto, “Studies on the structural and electrical properties of spray deposited ...” Philos.
Mag. B.68, pp. 215-218, 1993.
[10] G.X. Wang, M.S. Park, D. Wexler, J. Chen, H.K. Liu, “Synthesis and characterization of one-di” Appl. Phys.
Lett.19, pp. 88-90, 2006.
[11] M.S. Park, G.X. Wang, Y.M.Kang, D. Wexler, S.X. Dou, H.K. Liu, “Maximum Li storage in Si nanowires for
the high capacity three ...” Angew. Chem. Int. Ed., 46, pp.750-752,2007.
[12] G.X. Wang, J.S. Park, D. Wexler, M.S. Park, J.H. Ahn, “Preparation of SnO2/Carbon Composite Hollow
Spheres and Their ...” Inorg.Chem.46, pp.4778-4780, 2007.
[13] C.J.Brinker, G.W. Sherer, “Preparation and characterization of ultra-thin sol–gel films” Sol-Gel Science.
Academic Press, San Diego, 1990.
[14] M.S. Park, Y.M. Kang, J.H. Kim, G.X. Wang, S.X. Dou, H.K. Liu, “SnO2 nanosheets grown on graphene
sheets with enhanced lithium ...” Carbon. 46, pp.35-38, 2008.
[15] M.S. Park, Y.M. Kang, G.X. Wang, S.X. Dou, H.K. Liu, “Structural and electrochemical properties of a porous
...” Adv. Funct. Mater.18, pp.455-458, 2008.
[16] G.X. Wang, J.S. Park, M.S. Park, X.L.Gou,”Nanostructured semiconducting metal oxides for use in gas
sensors” Sensor and Actuators B: Chemical., 8, pp. 265-270, 2008.
[17] M.S. Park, G.X. Wang, S.Y. Kim, Y.M. Kang, H.K. Liu, S.X. Dou, “Synthesis of Tin Dioxide Octahedral
Nanoparticles with Exposed ...” Electrochem. Commun.9, pp.71-75, 2007.
[18] Z.W. Pan, Z.R .Dai, Z.L .Wang, “Nanoengineering of structural, functional, and smart materials” Science. 291,
pp.1947-1950, 2001.
[19] G .Spezia, “The growth and properties of large crystals of synthetic quartz.” Atti.Accad. Sci. Torino. 44, pp. 9599,1909.
[20] R.I .Walton, “General synthesis of metal sulfides nanocrystallines via a simple ...” Chem. Soc. Rev. 31, pp.
230-232, 2002.
[21] K.F .Zhang, S.J. Bao, X.Liu, J .Shi, “Vanadium dioxide nanobelts: Hydrothermal synthesis and magnetic ...”
Materials Research Bulletin. 41, pp.1985-1988, 2006.
[22] H.T.Feng, R.F.Zhuo ,J.T.Chen, D.Yan, J.J.Feng, H.J.Li, S.Cheng,P.X.Yan, “Synthesis, Characterization, and
Microwave Absorption Property of ...” Physica E. 41, pp.1640-1642, 2009.
[23] Hyoun Woo Kim, “SnO2microparticles by thermal evaporation and their properties ...” Seung Hyun Shim,
Chongmu Lee, CeramicsInternation. 32, 943-946, 2006.
[24] Zhengtao Deng, Bo Peng, Dong Chen, Fangqiong Tang, and Anthony J. Muscat, “Orientated Attachment
Assisted Self-Assembly of Sb2O3Nanorods ...” Langmuir. 24, 11089-11095, 2008.
[25] J. Wang, D. Zhou, P. Fraundorf and J. Liu , “Synthesis and Characterization of Antimony-doped Tin Oxide ...”
MicroscMicroanal. 13, 2-4, 2007.
[26] O. Lupan, L.Chow ,G.Chai, H.Heinrich, S.Park, A.Schulte , “Synthesis of one-dimensional SnO2nanorods via a
hydrothermal ...” Physica E. 41, 533-534, 2009.
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