Indian Journal of Pure & Applied Physics
Vol 46, May 2008, pp. 321-324
Synthesis of CdIn2S4 by flux method
L A Patil* & M D Mahanubhav
PG Department of Physics, Pratap College, Amalner 425 401
*E-mail: lapresearch@rediffmail.com
Received 12 December 2007; accepted 5 March 2008
Stoichiometric and non-stoichiometric powders of CdIn2S4 have been synthesized by flux method. X-ray diffraction
(XRD) studies reveal that CdIn2S4 powders are polycrystalline in nature with spinel cubic structure. Thick films of CdIn 2S4
powders have been prepared using screen printing technique on glass substrates. The films are characterized by energy
dispersive X-ray analysis (EDAX) for quantitative elemental analysis, scanning electron microscopy (SEM) for
microstructural studies and optical absorption studies for determination of band gap energies. The optical band gap energy
for stoichiometric film is observed to be 2.38 eV while for nonstoichiometric films, it increases as the Cd/In ratio increases.
Keywords: CdIn2S4, Flux method, Screen printing, Thick films, Absorption spectra
1 Introduction
Cadmium indium sulphide (CdIn2S4) is a
semiconducting ternary compound of type AIIB2IIIX4VI
where A = Cd, Zn, Hg or Mg, B = Ga or In and X = S,
Se, or Te. It crystallizes in cubic spinel structure. Bulk
crystals of CdIn2S4 are photosensitive in the visible
region1,2 and exhibit photoluminescence in the nearIR region3. CdIn2S4 is one of the photoconducting
materials and have the potential capabilities for the
applications in solar cells and light emitting diodes4,5.
Bulk crystals of CdIn2S4 were grown by chemical
transport and the Bridgman method over the past few
years6,7. Also, the thin films of CdIn2S4, deposited
using vacuum evaporation8-10, have been studied.
Hong11 prepared CdIn2S4 epilayers by hot wall epitaxy
method. There are no reports at all on the preparation
of CdIn2S4 by flux method. Flux method is a simple
technique to synthesize high quality homogeneous
solid solutions with potentials of up-scaling. It
permits the synthesis of solid solutions well below the
melting point of the materials12-14. Doping with
suitable elements can be easily achieved.
Stoichiometric and nonstoichiometric forms of solid
solutions are obtainable. Equipments required are
simple and within the financial scope of most
laboratories.
In the present study, structural and optical
properties of CdIn2S4 have been studied and reported.
CdIn2S4 powders are synthesized by flux method. The
thick films of as prepared stoichiometric and
nonstoichiometric powders of CdIn2S4 are prepared by
using screen printing technique. Screen printing is a
viable and economical method to produce thick films
of various materials.
2 Experimental Details
2.1 Synthesis of CdIn2S4 powders
CdIn2S4 powders were prepared by flux method
using sodium polysulphide (Na2Sx) as a flux. Na2Sx
solvents are reported to be suitable fluxes to
synthesize metallic sulphides15. The advantages of
Na2Sx solvents are the presence of common anion and
the possible byproduct related to sodium are soluble
in water and could be removed out from final product
(CdIn2S4). Na2Sx are soluble in cold water and can be
easily separated from the final product.
The starting materials used for the preparation of
CdIn2S4 were AR grade powders of cadmium
sulphide, indium sulphate, sulphur and sodium
sulphide. The above powders were mixed in
appropriate proportion so as to obtain stoichiometric
CdIn2S4 product. The mixture was ball-milled for 2 h
and then transferred into 50 ml platinum crucible. The
crucible was placed in kanthal wound muffle furnace
having temperature control of ± 2 oC. The furnace
temperature was increased to 600 oC with a heating
rate of 60 oC/h. This temperature was then maintained
for 1 h. The Cr-Al thermocouple was used to sense
the temperature of the furnace. During heating excess
sulphur would evaporate and it combines with air
oxygen and water in sodium sulphide to form SO2 and
H2S, respectively. The furnace was then switched off
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INDIAN J PURE & APPL PHYS, VOL 46, MAY 2008
to allow it to cool down to room temperature
overnight. The product in the crucible was washed
several times with double distilled water. Sodium
polysulphide got dissolved in water and separated out
easily. Final product was dried. Using the same
procedure and varying the proportion of cadmium
source (CdS), two different nonstoichiometric
powders were prepared.
2.2 Preparation of CdIn2S4 thick films
CdIn2S4 powder was thoroughly ground in an agate
pestle-mortar using double distilled acetone to ensure
a sufficiently fine particle size. The thixotropic paste
was formulated by mixing the fine powder of CdIn2S4
with solution of ethyl cellulose (a temporary binder)
in a mixture of organic solvents such as butyl
cellosolve, butyl carbitol acetate and terpineol.
Fluidity of the paste depends upon the extent of
organic part, which goes in its formulation16 (i.e. solid
to liquid ratio). The ratio of inorganic part to organic
part was kept as 75:25 in formulating paste. This
particular ratio for the paste formulation was found to
be thixotropic in nature and gave good line definition
of the prints. This paste was screen printed using a
160 mesh size screen and a flexible squeegee onto
glass substrates. The wet films were dried under IR
lamp and then fired at 200 oC for 30 min to remove
organic binder. The firing would mature the thick film
elements and bound them integrally to the substrates.
2.3 Characterization
The structural properties of powders were studied
with X-ray diffractogram (Philips PW 1730) using Cu
K radiation (=1.5418 Å)with Ni filter in scanning
angle range 20-80 º. Scanning electron microscope
(JEOL JSM-6360A) was used to examine the surface
morphology of the films. Quantitative elemental
analysis of the films was carried out by computer
controlled energy dispersive X-ray analyzer attached
to the scanning electron microscope. The optical
absorption spectra were recorded against wavelengths
300-900 nm using UV-VIS-NIR spectrophotometer
(HITACHI Model 330).
3 Results and Discussion
Table 1— Elemental composition of CdIn2S4 thick films
Sample wt % of the elements
No.
in film
Cd
S1
S2
S3
In
S
14.83 58.44 26.74
23.74 49.27 26.99
31.66 41.78 26.56
at % of the elements in film
Cd
In
S
Cd/In
8.95
14.26
19.12
34.54
28.98
24.71
56.52
56.76
56.17
0.259
0.492
0.774
The theoretically expected at % of Cd, In and S for
stoichiometric CdIn2S4 is 14.29, 28.57 and 57.14 %
respectively. It is clear from Table 1 that sample S2 is
stoichiometric while S1 is cadmium deficient and S3
is cadmium excess. Thus S1 and S3 thick films are
nonstoichiometric.
3.2 XRD analysis
Fig. 1 shows XRD patterns of CdIn2S4 powders
prepared by flux method. It is seen in all samples that
the peaks corresponding to (311) and (440) which are
the main characteristics of the cubic spinel phase of
CdIn2S4 (ASTM data file no. 31-229 and 27-60) are
present. Along with the peaks of CdIn2S4, few
additional peaks of βIn2S3 phase (ASTM data file no.
32-456) and CdS hexagonal phase (ASTM data file
no. 6-314) are also present. Sharp XRD peaks indicate
the polycrystalline nature of CdIn2S4.
The grain size of the samples was calculated using
the Debye-Scherrer formula
D = 0.9λ / βcosθ
where D is the diameter of the crystallites, λ is the
wavelength of the Cu K line, β is FWHM and θ is the
Bragg angle. The grain size values obtained for S1, S2
and S3 samples are 466, 432 and 495 nm, respectively.
3.3 Surface morphology
Surface morphology of CdIn2S4 thick films was
analyzed using SEM technique. Fig. 2 depicts SEM
pictures of samples S1, S2 and S3. SEM images
consists of voids and grains of varying sizes ranging
from 1 to 10 m. Along with the smaller spherical
grains there are few large grains tending to hexagonal
shape. The hexagonal grains could be attributed to the
CdS hexagonal phase present in the samples.
3.1 Elemental composition
Energy dispersive X-ray analysis (EDAX) was
employed to determine the elemental composition of
the films. The wt % and at % of Cd, In and S were
obtained by EDAX at three different locations on the
surface of the each film and average of the three is
given in Table 1.
3.4 Optical properties
The absorption spectra of the samples (S1-S3) were
recorded in the wavelength range 300-900 nm using
UV-VIS-NIR spectrophotometer. The variation of
absorbance with wavelength for samples is shown in
Fig. 3. It is clear from this figure that with the
PATIL & MAHANUBHAV: SYNTHESIS OF CdIn2S4 BY FLUX
Fig. 1 — XRD patterns of CdIn2S4 powders. (a) S1 (b) S2 (c) S3
Fig 2 — SEM micrographs of CdIn2S4. (a) S1 (b) S2 (c) S3
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INDIAN J PURE & APPL PHYS, VOL 46, MAY 2008
324
blue shift with increase in Cd/In ratio. The direct band
gap energy of stoichiometric CdIn2S4 is estimated to
be 2.38 eV and that of cadmium deficient and
cadmium excess films are 2.07 and 2.69 eV,
respectively.
Acknowledgement
Authors are grateful to Head, Department of
Physics and Principal, Pratap College, Amalner, for
providing laboratory facilities. One of the authors
(MDM) sincerely thanks the University Grants
Commission, Govt. of India, for sanctioning a
Teacher Fellowship. He also acknowledges Principal,
Z B Patil College, Dhule, for encouragement and
constant support to carry out this research work.
Fig. 3 — Absorption spectra of CdIn2S4 thick films
Table 2 — The band gap energies of CdIn2S4 thick film samples
Sample No. Cd/In Absorption edge at (nm)
S1
S2
S3
0.259
0.492
0.774
600
520
460
Band gap (eV)
References
2.07
2.38
2.69
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increase of Cd/In ratio, the absorption edge shifts
towards the lower wavelength side and there is blue
shift in absorption edge. The band gap energy Eg of
the films is determined from Fig. 3 and presented in
Table 2.
It is clear from Table 2 that band gap increases
from 2.07 to 2.69 eV with increase of Cd/In ratio
from 0.259 to 0.774. The band gap energy of the
stoichiometric film (S2) is observed to be 2.38 eV,
which is in the reported2 range from 2.10 to 2.42 eV.
4 Conclusions
The flux method is suitable for the synthesis of
CdIn2S4 powder. Stoichiometric and nonstoichiometric CdIn2S4 material can be synthesized by flux
method. CdIn2S4 powders are found to be
polycrystalline in nature. Absorption spectra showed
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