Impedance spectroscopic studies on pani ceo2 composites

INTERNATIONAL Electrical EngineeringELECTRICAL ENGINEERING
International Journal of
JOURNAL OF and Technology (IJEET), ISSN 0976 –
6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 1, January- February (2013), © IAEME
& TECHNOLOGY (IJEET)
ISSN 0976 – 6545(Print)
ISSN 0976 – 6553(Online)
Volume 4, Issue 1, January- February (2013), pp.01-08
IJEET
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IMPEDANCE SPECTROSCOPIC STUDIES ON PANI/CEO2
COMPOSITES

Khened B.S1, Machappa.T2, M.V.N. Ambika Prasad3, Sasikala. M.4*
1
Department of Electrical and Electronics Engineering,
Ballari Institute of Technology & Management, Bellary-583 104, Karnataka, India
2
Department of Physics, Ballari Institute of Technology & Management, Bellary-583 104,
Karnataka, India
3
Department of Material Science, Gulbarga University, Gulbarga-585 106, Karnataka, India
4
Department of Electrical and Electronics Engineering, C. V. R. College of Engineering,
Vastunagar, Ibrahimpatnam-501 510, R R Dist., Andhra Pradesh, India
Email: bskhened@yahoo.co.in, machappat@rediffmail.com,
Prasad1_Amb@rediffmail.com, sasi_mun@rediffmail.com

Author for correspondence: sasi_mun@rediffmail.com

ABSTRACT

Polyaniline-Cerium oxide composites were prepared by in situ polymerization
method with different weight percentage of cerium oxide in Polyaniline. The composites
were characterized by infrared spectroscopy (FTIR) and scanning electron microscopy
(SEM). The frequency dependent conductivity and dielectric behavior of these composites
have been studied in the frequency range of 50 Hz to 5 MHz. The variation of σac was small
in all composites in the frequency range of 50Hz to 10 KHz. Large variations in conductivity
were observed in the frequency range of 10 KHz to 5 MHz. This multiphase variation may
be due to lattice polarization around a charge in localized state and due to variation of
distribution of CeO2 in polymer matrix. Dielectric constant and dielectric loss and real part of
impedance were found to decrease with increase in frequency. The position of peak of Z''
shifts towards higher frequency side with decrease in weight percent of cerium oxide in
polyaniline.

Key words: polyaniline, Cerium oxide, impedance spectroscopy, a.c.conductivity

1

International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –

1. INTRODUCTION

Conducting polymers are being used commonly in scientific and industrial studies
and in various applications such as sensors, rechargeable batteries, diodes, transistors and
microelectronic devices [1-7]. These materials provide huge scope for tuning their electrical
conductivity [8-9]. Among conjugated polymers polyaniline deserves special attention
because of its good environmental stability, easy processability, moderate electrical
conductivity, and rich physics in charge transport mechanism [10].
The electrical and dielectric properties of these materials are altered when they are
taken in the composite form. The composite materials consist of conducting filler material in
the polymer matrix and provide satisfactory mechanical and electrical properties. Conducting
polymer inorganic composites have been in the extensive research for the past few years [11-
14]. Synthesis of many polyaniline—inorganic particle composites have been reported [15-
21] and applications of such composites as electro—rheological fluids [22] and in high
density information storage devices [23] have been studied.

The conductivity of these composites depends on number of factors such as the
concentration of conducting fillers, their shape, size, orientation and interfacial interaction
between filler molecules and host matrix [24-25]. Conduction by polarons and bipolarons is
the dominant mechanism of charge transport in polymers. New models are developed to
explain the mechanism of charge transport in these materials [26-27]. Kivelson was the first
to use the inter-soliton hopping model [28]. Other models like electron hopping and dipolar
relaxation have been used to explain the dielectric data of PANI salts. But it seems that no
definite theory exists to explain the origin of electric conduction or the reported near metal
insulator transition occurring in conducting PANI [29]. In the present paper, the authors
report the preparation of Polyaniline / Cerium oxide composites, its characterization through
FTIR spectra, scanning electron microscope (SEM), transport properties such as ac
conductivity, dielectric behavior, dielectric loss and variation of impedance with frequency.

2. EXPERIMENTAL

All chemicals used are analytical grade (AR) and were used as received. The
monomer aniline was doubly distilled prior to use. Synthesis of polyaniline /CeO2 composites
has been carried out by single step in situ polymerization technique. Aniline of 0.1mol was
dissolved in 1M of hydrochloric acid to form aniline hydrochloride. Finely grinded powder of
Cerium oxide (CeO2) is added in the weight percent of10, 20, 30, 40 and 50 to the above
solution with vigorous stirring to keep Cerium oxide suspended in the solution. To this
reaction mixture, 0.1M of oxidizing agent ammonium persulphate [(NH4)2S2O8] in 1M of
hydrochloric acid was added slowly with continuous stirring for 4–8 hours at 0–5° C to
polymerize. The precipitated powder was recovered, vacuum filtered and washed with de
ionized water. Finally, the resultant precipitate was dried in an oven for 24 hours to achieve
constant weight. In this way, five different composites of polyaniline/CeO2 with different
weight of (10, 20, 30, 40 & 50) in PANI have been synthesized. The pellets of 10 mm
diameter are formed with thickness varying up to 2 mm by applying pressure of 10 ton in a
UTM-40 machine (40 Ton Universal testing machine). For conductivity measurement, the
pellets are coated with silver paste on either side of the surfaces.

2


The characterization studies are employed on all the above synthesized
polyaniline/CeO2 composites to confirm the presence of CeO2 in PANI. Fourier transform
infrared(FTIR) spectra was recorded on a JASCO FT/IR 5300 spectrophotometer in KBr
medium and the powder morphology of pellets was investigated with scanning electron
micrographs on Phillips XL 30 ESEM
The frequency dependent AC conductivity studies on polyaniline / CeO2
composites are made using Hioki impedance analyzer (model 3532-50 programmable LCR
meter) in the frequency range 50 Hz to 5 MHz at room temperature.

3. RESULTS AND DISCUSSIONS

3.1. FTIR
Figure 1(a) shows the IR spectra of Polyaniline where the transmittance is plotted
as a function of wave number (cm-1). Careful analysis of the spectra reveals the presence of
intensity peaks 1302 cm-1 for C-N stretching + C-H bending,1240cm-1 C-N stretching + C-C
stretching ,812 cm-1 Deformational C-H (out of plane) of 1-4 disubstituted aromatic ring (
Benzoid).The spectra shows the presence intense bands at 1568 cm-1, 1481 cm-1 which may
be attributed to Qunoid and Benzoid rings respectively.

Figure 1 (a) IR spectrum of Polyaniline (b) IR spectrum of composite

The IR spectra of polyaniline – CeO2 composite (40 wt % of CeO2 in PANI) is
shown in Figure 1 (b). The prominent peaks that are observed in polyaniline – CeO2
composite are 2918 cm-1, 2361 cm-1, 1560 cm-1, 1471 cm-1, 1298 cm-1, 1240cm-1,1107 cm-
1
,798 cm-1, 652 cm-1,and 509 cm-1.By careful observation of IR the characteristic stretching
frequencies are considerably shifted towards higher frequency side. The data suggest that,
there is a Vander walls kind of interaction between the polymer chain and CeO2.

3


3.2. SEM
SEM micrograph of polyaniline is as shown in figure 2(a). It can be clearly seen
that the micrograph of polyaniline is smooth and homogeneous. Since Hydrochloric acid is
used as protonic acid in the preparation of polyaniline, the presence of microcrystalline
structure can be seen that is not homogeneously distributed throughout. The contrast in the
image is a result of differences in scattering from different areas of the surface as a result of
geometrical differences.
Figure 2(b) shows the SEM micrograph of pure CeO2. High magnification SEM
image reveals that CeO2 particles are uniformly distributed with definite shape and size and
confirms the crystallanity of the oxide.The SEM micrograph of polyaniline – CeO2 composite
with 40 wt % of CeO2 in polyaniline is shown in figure 2(c). High magnification SEM image
reveals the presence of CeO2 particles uniformly distributed throughout the composite
sample. A small variation in the particle dimensions of CeO2 so dispersed in polyaniline has
been observed. Fibrillar morphology is observed in the composite. The contrast in the image
is due to the difference in scattering from different surface areas as a result of geometrical
differences between polyaniline and CeO2.

Figure 2.SEM of (a) PANi, (b)CeO2, (c)composite

3.3. A.C. conductivity
Using the values of the equivalent parallel capacitance(Cp), dissipation factor( D),
and parallel equivalent resistance(Rp), recorded by the LCR meter at a different frequencies ,
ac conductivity (σac), dielectric constant (ε') and dielectric loss (tan δ) parameters have been
calculated. Figure 3(a), shows the variation of ac conductivity as a function of frequency of
polyaniline/CeO2 composites. It is observed that variation of σac is small in all composites
in the frequency range of 50Hz to 10 KHz. Large variations in conductivity is observed in
the frequency range of 10 KHz to 5 MHz. This multiphase variation may be due to lattice
polarization around a charge in localized state and due to the variation of distribution of CeO2
in polymer matrix. Apart from temperature and frequency, percentage of crystallinity, degree
of protonation, crystalline domain size and order in crystalline and amorphous regions have a
relation with the delocalization length.
Figure (3b) shows the variation of σac as a function of wt% of CeO2 in polyaniline
at three frequencies (10, 100 & 1000 kHz) at room temperature. It is observed that ac
conductivity decreases in 10, 20, 30 & 50 wt % of CeO2 in polyaniline and increases in 40 wt
% of CeO2 in polyaniline. The decrease in conductivity with increase in wt% may be due to
an increase in the disorderliness of the composites. CeO2 particles could possibly induce
conformational changes in polyaniline, leading to a reduction in the order and a consequent
reduction in the delocalization length, which is reflected with decrease in conductivity [32].

4


The increase in conductivity in 40 wt% of CeO2 in polyaniline may be due to the extended
chain length of polyaniline which facilitate the polarization of charge carriers and variation of
distribution CeO2 particles which may support for more number of charge carriers to polarize
between favorable localized sites causing increase in conductivity.
-2
1.0x10 0.0050
10 20 30 40 50

-3 0.0045 b 10 wt%
9.0x10 10 KHz

0.0040
100KHz
1000KHz 20 wt%
-3
8.0x10 0.0035 30 wt%
40 wt%

conductivity(s-cm )
0.0030

-1
-3
7.0x10 0.0025 50 wt%
c o n d u c tiv ity (s /c m ) -3
0.0020

6.0x10
0.0015

-3 0.0010
5.0x10
0.0005

-3
4.0x10 0.0000
10 20 30 40 50
wt% of CeO2 in Polyaniline
-3
3.0x10
a
-3
2.0x10
-3
1.0x10

0.0
100 1000 10000 100000 1000000
frequency(Hz)

Figure 3(a) ac conductivity as a function of frequency (b) variation of σac at three frequencies.

3.4 Dielectric Behaviour
Figure 4 shows the variation of ε as a function of frequency for different wt% of
polyaniline/ CeO2 composites. It is observed that, the dielectric constant is high in 20 wt %
compared to 10, 30, 40 & 50 wt% at low frequency .In all the samples, dielectric constant
decreases with increase in applied frequency. The dielectric constant value for different
composites is ranging from 8.9 x 105 to 3.26 x 106 at 50 Hz which decreases to value ranging
from 707 to1843 at 5 MHz. Such large values of real permittivity is not unusual, which are
related to effect of electrode polarization and space charge polarization [30]. The observed
behavior may be due to nearly a Debye-type single relaxation mechanism taking place in
these materials. All these results go in accordance with the conductivity behavior.

6
3.5x10
10 wt% 10 10 wt%
20 wt% 20 wt%
6
3.0x10 30 wt% 30 wt%
40 wt% 40 wt%
50 wt% 50 wt%
6 8
2.5x10

6
2.0x10
6
T nd lta
a e
e'

6
1.5x10

6 4
1.0x10

5
5.0x10
2

0.0

-5.0x10
5 0
100 1000 10000 100000 1000000 100 1000 10000 100000 1000000
Frequency(Hz) Frequency(Hz)

Figure 4. Variation of permittivity Figure 5 . variation of dielectric loss

5


3.5. Dielectric loss
The variation of dielectric loss as a function of frequency for different wt% of
polyaniline / CeO2 composites is represented in figure 5. The loss tangent value is ranging
between 4.06 to 9.99 at 50 Hz and decreases with increase in frequency. At 5 MHz its value
is ranging between0.68 to 1.89.Similar values which increase with protonation have been
reported earlier [31] . The observed behavior is in accordance with the conductivity and
dielectric constant results in these composites. High dissipation loss at low frequency in all
the composites may be due to DC conduction losses.
3
4.0x10 900

3 10wt% 800 10wt%
3.5x10
20wt% 20wt%
30wt% 700 30wt%
3
3.0x10 40w t% 40w t%
50w t% 600 50w t%
3
2.5x10
500
z"(Ohms)

3
2.0x10
z'

400
3
1.5x10
300
3
1.0x10
200

2
5.0x10 100

0.0 0
1 2 3 4 5 6 7 1 2 3 4 5 6 7
10 10 10 10 10 10 10 10 10 10 10 10 10 10
Frequency(Hz) Frequency (Hz)

900

800
Z''(ohms)

700

600

500

400

300
10 %
200 20 %
30 %
100 40 %
50 %
0
0.0 5.0x102 1.0x103 1.5x103 2.0x103 2.5x103 3.0x103 3.5x103 4.0x103

Z'(ohms)

Figure 6 (a)Variation of Z' with frequency (b) Variation of Z'' with frequency (c)Nyquist plot

Figure 6 (a) shows the variation of real part of impedance with frequency in
polyaniline / CeO2 composites. At lower frequencies the value of Z' increases with increase
in weight percent of cerium oxide in polyaniline and with increase in frequency, the value of
Z' is found to decrease in all samples. The variation of imaginary part of impedance with
frequency in polyaniline / CeO2 composites is shown in figure 6(b)..The position of peak of
Z'' shifts towards higher frequency side with decrease in weight percent of cerium oxide in
6


polyaniline. The width of the peak points towards the possibility of distribution of relaxation
times(33) and the relaxation time τ can be determined from the position of the peak
(τ=1/ωmax). Figure 6(c) shows Nyquist (Z' vs. Z'') plots for polyaniline / CeO2 composites.
The semi circles observed in the plot are due to grains, grain boundaries and grain- electrode
effect. With increase in weight percent of cerium oxide in polyaniline, the number of semi-
circles increases up to three. Each semi circle can be represented by a resistance and a
capacitor connected in parallel. The intercept on real axis represents the bulk resistance of the
sample.

4. CONCLUSIONS

Polyaniline-cerium oxide composites with different weight percentage of cerium
oxide in Polyaniline were prepared by in situ polymerization method. The formations of the
composites were characterized by infrared spectroscopy, x-ray diffraction and scanning
electron microscope techniques. The frequency dependent conductivity and dielectric
behavior of the composites have been studied in the frequency range of 50 Hz to 5 MHz. In
the frequency range of 50Hz to 10 KHz, variations in a.c. conductivity was small in all the
samples. Large variations in conductivity were observed in the frequency range of 10 KHz to
5 MHz. This multiphase variation may be due to lattice polarization around a charge in
localized state and due to variation of distribution of CeO2 in polymer matrix. With increase
in frequency, dielectric constant was found to decrease. This behavior may be due to nearly a
Debye-type single relaxation mechanism. High dissipation loss observed at low frequency
may be due to D.C. conduction losses. With increase in frequency the dielectric loss and Z'
were found to decrease. With decrease in weight percent of cerium oxide in polyaniline, the
position of peak of Z'' shifts towards higher frequency side.

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