Structural, optical and microscopic studies of tungsten substituted molybdenum diselenide thin films

Article abstract of DOI:10.1016/j.jallcom.2010.03.146

A modified chemical bath deposition method has been developed to prepare Mo_1-xW_xSe₂ layer type semiconductor thin films. Various preparative conditions of the thin films are outlined. The films were characterized by X-ray diffraction, optical absorption, electrical measurements and thermoelectric techniques. The grown films were found to be uniform, well adherent to substrate and brown in color. The X-ray diffraction (XRD) study indicates the polycrystalline nature in single hexagonal phase over whole range of composition. Analysis of absorption spectra gave direct type of band gap, the magnitude of which increases slightly as tungsten content in the film is increased and electrical conductivity at room temperature was found to be 10^-5 to 10^-2 (Ω cm)^-1. All the films show n-type conductivity.

Full text of DOI:10.1016/j.jallcom.2010.03.146

Journal of Alloys and Compounds 499 (2010) 187–193
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
Structural, optical and microscopic studies of tungsten substituted
molybdenum diselenide thin films
D.J. Sathed,∗, P.P. Hankarea, A.H. Maniksheteb, P.A. Chatec, A.A. Patila
a Solid State Research Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur, MS, India
b Dept. of Chemistry, Walchand college, Solapur, MS, India
c Dept. of Chemistry, J.S.M. College, Alibag, MS, India
d Dept. of Chemistry, KIT’s College of Engineering, Kolhapur, MS, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A modified chemical bath deposition method has been developed to prepare Mo1−xWxSe2 layer type
semiconductor thin films. Various preparative conditions of the thin films are outlined. The films were
characterized by X-ray diffraction, optical absorption, electrical measurements and thermoelectric tech-
niques. The grown films were found to be uniform, well adherent to substrate and brown in color. The
X-ray diffraction (XRD) study indicates the polycrystalline nature in single hexagonal phase over whole
range of composition. Analysis of absorption spectra gave direct type of band gap, the magnitude of
which increases slightly as tungsten content in the film is increased and electrical conductivity at room
temperature was found to be 10−5 to 10−2 (ꢀ cm)−1. All the films show n-type conductivity.
© 2010 Elsevier B.V. All rights reserved.
Received 10 August 2009
Received in revised form 13 March 2010
Accepted 18 March 2010
Available online 23 March 2010
Keywords:
Thin films
Semiconductors
Chemical synthesis
X-ray diffraction
1. Introduction
MoxW1−xSe2 by using various methods have been published earlier
[17,18,21].
The transition metal dichalcogenides (MoSe2, WSe2, MoS2, and
WS2) have layered structure and attracted many researchers due to
their interesting properties like superconductivity, charge density
waves, intercalation compound formation etc. Most of the TMDC
compounds studied can be considered structurally as strongly
bonded two-dimensional X–M–X (M = metal, X = chalcogen) lay-
ers loosely coupled to one another by relatively weak van der
Waals type forces [1–4]. Recent investigations have shown that the
layered type semiconducting group VI transition metal dichalco-
genides, which absorb visible and near-IR light are particularly
interesting materials for photoelectrochemical solar energy con-
version. Recent applications include intercalation compounds,
long-life PEC solar cells, catalysis in hydro treating processes
high temperature- high pressure solid lubricants, and recharge-
able batteries [5–11]. Agarwal et al. described the growth and
some of the key properties of Mo1−xWxSe2, WSxSe2−x, MoSexTe2−x
and Mo0.5W0.5Se2 single crystals [12–16]. Similar mixed crys-
tals of compounds such as Mo0.02W0.98Se2, Mo0.5W0.5Se2 and
In the present investigation we describe synthesis of
Mo1−xWxSe2 thin films grown on glass substrates by chemi-
cal method. Structural, morphological, optical, and electrical
properties of sample were study and reported.
2. Experimental details
All the solutions were exclusively prepared in double-distilled water and the
basic chemicals used were of AR grade. All the solutions were kept in air tight bot-
tles. It contains ammonium molybdate, sodium tungestate, tartaric acid, hydrazine
hydrate, sodium sulphite and selenium powder. Sodium selenosulphate was pre-
pared by following the reported method [19].
The deposition of typical Mo0.5W0.5Se2 thin films was made in a reactive solu-
tion obtained by mixing 5 mL (0.2 M) ammonium molybdate, 5 mL (0.2 M) sodium
tungestate, 5 mL (1 M) tartaric acid, 20 mL (10%) hydrazine hydrate and 20 mL
(0.25 M) sodium selenosulphate. The total volume of the reaction mixture was made
to 200 mL by adding double-distilled water. The beaker containing the reactive
solution was transferred to an ice bath of 278 K temperature. The pH the result-
ing solution was found to be 9.5–10.5. Four clean glass slides were kept vertically
enflaged on a specially designed substrate holder and rotated in the reaction mix-
ture with a speed at 50 2 rpm. The temperature of the solution was then allowed
to rise slowly to 298 K. The substrates were removed from the beaker after 3 h. After
the deposition, the substrates were taken from the bath, rinsed with distilled water,
dried in air and kept in a dessicator.
A similar procedure was adapted to synthesis Mo1−xWxSe2 thin films. The solu-
tions of ammonium molybdate, sodium tungestate and sodium selenosulphate were
mixed in the required stoichiometric ratio 1:1:2. The pH of the reactive solution was
kept in the range 9.5–10.5.
∗
Corresponding author.
E-mail addresses: djsathe07@yahoo.co.uk (D.J. Sathe),
pachate04@rediffmail.com (P.A. Chate).
0925-8388/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2010.03.146

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D.J. Sathe et al. / Journal of Alloys and Compounds 499 (2010) 187–193
Fig. 1. (a) A plot of thickness vs. time for representative Mo0.5
W0.5Se2 thin film. (b)
A plot of thickness vs. temperature for Mo0.5W0.5Se2 thin film.
3. Growth mechanism of Mo1−xWxSe2 thin films
The rate of deposition of Mo1−xWxSe2 film depends upon super-
saturation, pH, composition of reactive species and temperature
of bath. Initially reaction mixture is prepared by mixing ammo-
nium molybdate, sodium tungestate, sodium selenosulphate and
tartaric acid as complexing agent. Tartaric acid controls the metal
ion concentration in the reaction vessel. Hydrazine hydrate acts as
a reducing agent and it also serves complementary complex to help
increase compactness and adherence of the film. A slow increase
in temperature decomposes moderately stable sodium selenosul-
phate to yield Se2−, while hydrazine hydrate reduce M6+ to M4+ in
basic medium. The dissociation of M-TA complex at higher temper-
ature liberates bear M4+ ions that react with Se2− ion to get brown
color thin film. The growth mechanism can be described from the
following reactions;
Fig. 2. XRD-pattern of Mo1−xWxSe2 thin films; (a) (x = 0.0, 0.2, 0.4) (b) (x = 0.6, 0.8,
1.0).
nucleation centers on the substrates. The presences of induction
period suggest ion-by-ion growth mechanism instead of cluster-
by-cluster.
The present investigation indicates that homogenous
Mo1−xWxSe2 films have been deposited at 180 min. The thickness
was measured every 30 min and plotted against time as shown
in Fig. 1(a). From the figure, the thickness varies linearly with
time, but above 180 min the concentration of the reactive species
decreases and results in decrease in thickness. All the films were
homogenous well adherent to the substrate. Growth kinetics for
the development of typical Mo0.5W0.5Se2 films is shown in Fig. 1(b)
50 2 rpm rotation speed was selected to deposit Mo1−xWxSe2
thin films. The optimum condition in the deposition process for
yielding good quality deposits are 298 K deposition tempera-
ture and 180 min deposition time. The films obtained were well
adherent and of brown color.
M
6+ + 3A2− → [M(A)3]
(M = Mo, W)
[M(A)3] + 2NH2-NH2 + 2OH− → M4+ + 3A + 2H2O + 2N2↑
Na2SeSO3 + OH− → Na2SO4 + HSe−
HSe− + OH− → H2O + Se2−
4. Sample characterization
(1 − x)[Mo(A)3] + x [W(A)3] + 2Se2− → Mo1−xWxSe2 + 3A
Crystallographic studies of films were characterized by using
In chemical bath deposition method, the ionic product exceeds
the solubility product; precipitation take place and ions combine on
the substrate and in the solution to form nuclei followed by growth
process. The film deposition takes place by recombination of ions on
the glass surface via nucleation followed by growth. The deposition
of film occurs when the ionic product of M4+ and Se2− exceeds the
solubility product. In the growth process, no film formation occurs
within first 60 min. This is the induction period required to from
a Phillips PW-1710 X-ray diffractometer with Cu K␣1 line
(ꢁ = 1.54056 Å) in 2␪ range from 10◦ to 80◦. The optical proper-
ties were studied by taking absorption spectra of films using a
Hitachi-330 (Japan) double-beam spectrophotometer in the range
from 400 to 900 nm at room temperature. A substrate absorption
correction was made by placing an identical uncoated glass slides
in the reference beam. A 250 MK-III, Stereoscan, Cambridge (UK)
scanning electron microscope (SEM) was used for microstructural

D.J. Sathe et al. / Journal of Alloys and Compounds 499 (2010) 187–193
189
Table 1
Crystallographic data of Mo1−xWxSe2 thin film.
Film compositions
Observed ‘d’ (Å)
Standard ‘d’ of MoSe2 (Å)
Standard ‘d’ of WSe2 (Å)
h k l planes
Cell parameters (Å)
Crystallite sizes (Å)
2.879
2.366
1.895
1.415
1.303
2.846
2.368
1.909
1.422
1.303
1 0 0
1 0 3
1 0 5
2 0 0
2 0 4
a = b = 3.281
c = 12.882
MoSe2
224
219
214
210
204
193
189
187
181
174
159
2.8863
2.4161
1.9951
1.5178
1.3137
2.846
2.368
1.909
1.422
1.303
1 0 0
1 0 3
1 0 5
2 0 0
2 0 4
a = b = 3.284
c = 12.893
Mo0.9W0.1Se2
Mo0.8W0.2Se2
Mo0.7W0.3Se2
2.9193
2.4645
2.0821
1.6137
1.3245
2.846
2.368
1.909
1.422
1.303
1 0 0
1 0 3
1 0 5
2 0 0
2 0 4
a = b = 3.289
c = 12.905
2.9671
2.5120
2.1680
1.7094
1.3352
2.846
2.368
1.909
1.422
1.303
1 0 0
1 0 3
1 0 5
2 0 0
2 0 4
a = b = 3.292
c = 12.914
3.0081
2.5609
2.2534
1.8043
1.3456
2.846
2.368
1.909
1.422
1.303
1 0 0
1 0 3
1 0 5
2 0 0
2 0 4
a = b = 3.298
c = 12.917
Mo0.6
W0.4Se2
3.0481
2.612
2.3397
1.904
2.846
2.368
1.909
1.422
1.303
1 0 0
1 0 3
1 0 5
2 0 0
2 0 4
a = b = 3.303
c = 12.929
Mo0.5W0.5Se2
Mo0.4WO.6Se2
Mo0.3WO.7Se2
Mo0.2W0.8Se2
Mo0.1W0.9Se2
WSe2
1.3567
3.0814
2.6872
2.4257
1.9969
1.3678
3.250
2.850
2.770
2.380
1.410
0 0 4
1 0 0
1 0 1
1 0 3
1 0 8
a = b = 3.307
c = 12.942
3.1283
2.7051
2.5117
2.0927
1.3779
3.250
2.850
2.770
2.380
1.410
0 0 4
1 0 0
1 0 1
1 0 3
1 0 8
a = b = 3.311
c = 12.952
3.1692
2.7537
2.5979
2.1885
1.3887
3.250
2.850
2.770
2.380
1.410
0 0 4
1 0 0
1 0 1
1 0 3
1 0 8
a = b = 3.317
c = 12.966
3.2093
2.8021
2.6839
2.2842
1.3991
3.250
2.850
2.770
2.380
1.410
0 0 4
1 0 0
1 0 1
1 0 3
1 0 8
a = b = 3.321
c = 12.976
3.250
2.851
2.775
2.382
1.413
3.250
2.850
2.770
2.380
1.410
0 0 4
1 0 0
1 0 1
1 0 3
1 0 8
a = b = 3.325
c = 13.00
observations. The electrical resistance measurements were carried
out in the temperature range 300–500 K on a Zintek 502 BC mil-
liohm meter using the two-probe method. A quick drying silver
paste was applied at the ends of the film for better ohmic contact.
Maintaining a temperature gradient along the length of the film
and measuring the potential difference across the terminals hav-
ing a separation of 1 cm with the help of digital micro-voltmeter
made thermoelectric power measurement. A calibrated thermo-
couple probe (chrome alumel) with a digital indicator was used to
sense the working temperature.
5. Result and discussion
5.1. XRD studies
The XRD-pattern of films were obtained by using a Phillips
PW-1710 X-ray diffractometer with Cu K␣1 line (ꢁ = 1.54056 Å)
in 2␪ range from 10◦ to 80◦. The XRD-pattern of representative
Mo1−xWxSe2 thin films are shown in Fig. 2(a) (x = 0.0, 0.2, 0.4) and
(b) (x = 0.6, 0.8, 1.0). The presence of a large number of peaks indi-
cates that the films are polycrystalline in nature. The observed ‘d’

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D.J. Sathe et al. / Journal of Alloys and Compounds 499 (2010) 187–193
Fig. 3. SEM photographs of various Mo1−xWxSe2 thin films (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0).
values for deposited samples were in good agreement with the
standard ‘d’ values taken from JCPDS diffraction file No. 15-0029
(MoSe2)and JCPDS-06-0080 (WSe2). Comparison of observed ‘d’
with standard ‘d’ values confirms that chemically deposited film
shows of single phase compound with typical lines belonging to
hexagonal structure in accordance with the literature reported data
[4,16,20].
At the experimental conditions, MoSe2 and Mo1−xWxSe2 films
with 0.0 < x ≤ 0.5 showed prominent peaks due to reflections from
(1 0 0), (1 0 3), (1 0 5), (2 0 0) and (2 0 4) planes of a hexagonal MoSe2
structure. A significant shift in peak position with changes in con-
centration was not observed and hence, it can be conjectured that
addition of tungsten ions in MoSe2 up to x < 0.5 forms alloy in
the form of a solid solution. A small increase in lattice parame-
ter is observed with the gradual addition of tungsten ions in MoSe2
and is in conformity with the probable solid solution formation in
terms of incorporation of tungsten ions in MoSe2. Since the ionic
radius of the tungsten ion is known to be slightly greater than the
molybdenum ion, additions of tungsten ions in MoSe2 gradually
expand the cell uniformly. Although, the X-ray diffraction pattern
shows a shift in diffraction line position, the number of lines is
not altered, which gives an evidence that the cell symmetry is not
changed by addition of tungsten. However, for higher values of x
(1.0 ≤ x ≤ 0.5), the entire films exhibited highest intensity reflec-
tion peak at d = 3.25 Å (0 0 4). Along with (0 0 4) plane (1 0 0), (1 0 1),
(1 0 3), (1 0 8) planes were peaks corresponding to hexagonal struc-
ture of WSe2.A small increase in lattice parameter is observed with
the gradual addition of tungsten ions in MoSe2.which indicates
that tungsten ions go into form solid solution with MoSe2. The lat-
tice parameters ‘a and c’ were found to be 3.28 Å and 12.882 Å for
MoSe2film and 3.325 Å 12.921 Å for WSe2 respectively. The vari-
ation of the lattice parameters as a function of composition ‘x’
and the results show that the values of ‘a’ and ‘c’ vary linearly
with ‘x’ following Vegard’s law [12]. The crystallite sizes of thin
films were determined by using Scherrer formula and listed in
Table 1.
5.2. Microscopic characterization
Scanning electron microscopy (SEM) is convenient technique to
study the surface morphology of thin films. The SEM micrographs
of Mo1−xWxSe2 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) thin films are shown
in Fig. 3. All the thin films are homogenous, well cover to glass sub-
strate and without any cracks or pinholes. The spherical grains are

D.J. Sathe et al. / Journal of Alloys and Compounds 499 (2010) 187–193
191
seen to be fused with adjacent. This type of morphology is typical
of layered structure [19,21,22].
5.3. Optical studies
The optical absorption spectra for Mo1−xWxSe2 films deposited
onto a glass substrate were obtained in the wavelength range of
400–900 nm without considering losses due to reflection and trans-
mission. Fig. 4(a) and (b) represents the absorption spectra of few
representative samples. The optical absorption studies revealed a
high absorption coefficient with allowed direct type of transition.
The interpretation of experimental results is most often per-
formed with the help of the formula derived for a 3D crystal. The
simplest form of the equation obeyed near and above the absorp-
tion edge is; [23]
˛hꢂ = A(hꢂ − Eg)1/2
A plot of (˛hꢂ)2 versus hꢂ should be a straight line whose inter-
cept to the x-axis gives the optical band gap. The graphs of (˛hꢂ)2
versus hꢂ for ‘as deposited’ samples are shown in Fig. 5(a) (x = 0.0,
0.2) (b) (x = 0.4, 0.6) and (c) (x = 0.8, 1.0) for samples. The band gaps
for various compositions slightly increase from 1.43 to 1.48 eV with
increase in mole fraction of tungsten (x).
5.4. Electrical & thermo electrical properties
The dark conductivity of all samples was measured by using
two-probe method in temperature range of 300–525 K. The spe-
cific conductance at room temperature of MoSe2 and WSe2 were
found to be of the order of 10−5 to 10−2(ꢀ cm)−1, respectively. The
specific conductance increases for the ternary films with composi-
tion parameters ‘x’. The values of specific conductance of different
composition at 300 and 525 K are listed in Table 2
The conductivity of the samples increases with increase in tem-
perature, showing semiconducting behavior of the films. The plot
of log ꢃ versus 1000/T is shown in Fig. 6(a and b). The plots are
linear for Mo1−xWxSe2 films indicating the presence of only one
type of conduction mechanism in the films. The activation energies
obtained from the slopes of straight lines of log ꢃ versus 1000/T
plots (Fig. 5) are included in Table 2. The values were found to be
between 0.683 and 0.990 eV at high temperature and 0.005 and
0.064 eV low temperatures. The values are in well agreement with
earlier reported values for MoSe2 and WSe2 thin films [24–27].
Thermoelectrical power measurement of all films shows sim-
ilar behavior of increasing thermoelectric power with increasing
temperature. The increase in thermoelectric power with tempera-
ture suggests the degenerate nature of the films. In thermoelectric
power measurements, the open circuits thermovoltage generated
by samples, when a temperature gradient is applied across 2-cm
length of samples was measured. From the sign of terminal con-
Fig. 4. Absorption spectra of Mo1−xWxSe2 thin film samples (a) for films with x = 0.0,
0.1, (b) for films with x = 0.2, 0.4, 0.6, 0.8.
Table 2
Electrical parameters of Mo1−xWxSe2 thin film.
Sr. No.
Composition
Specific conductance (ꢀ cm)−1
Activation energy (eV)
HT
At 300 K
At 525 K
LT
01
02
03
04
05
06
07
08
09
10
11
MoSe2
2.7 × 10−5
5.45 × 10−3
4.49 × 10−3
3.58 × 10−3
3.28 × 10−3
8.46 × 10−3
2.18 × 10−3
5.32 × 10−3
1.64 × 10−3
5.62 × 10−2
1.32 × 10−2
2.77 × 10−1
0.683
0.706
0.702
0.741
0.773
0.797
0.829
0.858
0.880
0.912
0.99
0.005
0.016
0.031
0.041
0.055
0.162
0.271
0.382
0.488
0.593
0.640
Mo0.9W0.1Se2
Mo0.8W0.2Se2
Mo0.7W0.3Se2
Mo0.6W0.4Se2
Mo0.5W0.5Se2
Mo0.4W0.6Se2
Mo0.3W0.7Se2
Mo0.2W0.8Se2
Mo0.1W0.9Se2
WSe2
3.25 × 10−5
3.92 × 10−5
4.14 × 10−5
4.59 × 10−5
8.33 × 10−5
9.50 × 10−5
7.14 × 10−5
1.35 × 10−4
6.25 × 10−3
1.58 × 10−2

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D.J. Sathe et al. / Journal of Alloys and Compounds 499 (2010) 187–193
Fig. 5. Determination of band gap for Mo1−xWxSe2 thin films.
Fig. 6. A plot of ‘log ꢃ’ with inverse of absolute temperature for Mo1−xWxSe2 thin films x = 0.1, 0.3, 0.5, 0.7, 0.9.

D.J. Sathe et al. / Journal of Alloys and Compounds 499 (2010) 187–193
193
nected to cold end of the sample, one can decide the sign of the
predominant charge carrier [28]. In our study, the negative termi-
nal was connected to cold end therefore all the film show n-type
conductivity.
[6] M.H. Whittingham, F. Levy (Eds.), Intercalated Layered Materials, Reidel, Dor-
drecht, 1979, p. 533.
[7] G. Prasad, O.N. Shrivastava, J. Phys. D: Appl. Phys. 21 (1988) 1028.
[8] G. Kline, K.K. Kam, D. Canfield, B.A. Parkinson, Solar Energy Mater. 4 (1980)
2471.
[9] H.D. Abruna, G.A. Hope, A.J. Bard, J. Electrochem. Soc. 29 (1982) 2224.
[10] K. Agarwal, V.V. Rao, Matter Sci. Lett. 9 (1996) 1023.
[11] R. Tenne, A. Woldm, Appl. Phys. Lett. 47 (1985) 707.
[12] M.K Agarwal, P.A. Wani, Mater. Res. Bull. 14 (1979) 825.
[13] M.K. Agarwal, P.A. Wani, P.D. Patel, J. Cryst. Growth 49 (1980) 693.
[14] M.K. Agarwal, L.T. Talell, Solid State Commun. 76 (1986) 549.
[15] M.K. Agarwal, M.N. Vashi, A.R. Jani, J. Cryst. Growth 71 (1985) 414.
[16] M.K. Agarwal, P.D. Patel, R.M. Joshi, J. Mater. Sci. Lett. 5 (1986) 66.
[17] W.K. Hofmann, H.J. Lewerern, C. Pettenkofer, Solar Energy Mater. 17 (1988)
165.
6. Conclusions
1. Mo1−xWxSe2 can be deposited at low temperature by a modified
chemical deposition technique.
2. The film formation takes place via nucleation and growth.
3. Crystallographic studies shows that Mo1−xWxSe2 exist in hexag-
onal structure. As the composition parameter (x) increases, the
‘d’ value, lattice parameter increases slightly.
[18] G. Kline, K.K. Kam, R. Ziegler, B.A. Parkinson, Solar Energy Mater. 6 (1982)
337.
[19] P.P. Hankare, A.H. Manikshete, D.J. Sathe, P.A. Chate, K.C. Rathod, J. Mater. Chem.
Phys. 113 (2009) 183.
[20] G Salitera, G. Hodes, E. Klein, R. Tenne, Thin Solid Films 245 (1994) 190.
[21] P.P. Hankare, A.H. Manikshete, D.J. Sathe, P.A. Chate, J. Mater. Sci.: Mater. Elec-
tron. 10854 (2009) 9980.
[22] P.P. Hankare, A.A. Patil, P.A. Chate, K.M. Garadkar, D.J. Sathe, A.H. Manikshete,
I.S. Mulla, J. Cryst. Growth 311 (2008) 15.
[23] P.P. Hankare, P.A. Chate, D.J. Sathe, A.A. Patil, J. Mater. Sci.: Mater. Electron. 20
(2009) 776.
4. Optical studies revealed the presence of direct band gap. The
band gap value slightly increases.
5. The specific conduction at room temperature of Mo1−xWxSe2
thin films were found to be of the order of 10−5 to 10−2(ꢀ cm)−1
.
References
[24] P.P. Hankare, P.A. Chate, S.D. Delekar, V.M. Bhuse, M.R. Asabe, B.V. Jadhav, K.M.
Garadkar, J. Cryst. Growth 291 (2006) 40.
[1] A. Jäger-Waldau, E. Bucher, Thin Solid Films 200 (1991) 157.
[2] M.K. Agarwal, H.B. Patel, K. Nagireddy, J. Cryst. Growth 41 (1977) 84.
[25] S. Mary Delphine, M. Jayachandran, C. Sanjeeviraja, Mater. Res. Bull. 40 (4)
(2005) 135.
[3] S. Mary Delphine, M. Jayachandran, C. Sanjeeviraja, Mater. Chem. Phys. 81
(2003) 78.
[26] J.C. Bernede, J. Pouzet, Z.K. Alaoui, Appl. Phys. A 51 (1990) 155.
[27] F. Fan, H. White, B.L. Wheeler, A.J. Bard, J. Electrochem. Soc. 127 (1980) 518.
[28] C.N. Rao, Modern Aspects of Solid state Chemistry, Plenum Press, New York,
1974.
[4] J. Devadasan, C. Sanjeeviraja, M. Jayachandran, Mater. Chem Phys. 77 (2003)
397.
[5] O. Wisser, S. Landa, Catalysts, Their Properties & Application, Pergamon, Oxford,
1973.