Conductivity of surface modified TiO2 dope nanocomposites

Conductivity of surface modified TiO2 dope nanocomposites

Measurement 60 (2015) 214–221 Contents lists available at ScienceDirect Measurement journal homepage: www.elsevier.com/locate/measurement Conductiv...

2MB Sizes 0 Downloads 25 Views

Measurement 60 (2015) 214–221

Contents lists available at ScienceDirect

Measurement journal homepage: www.elsevier.com/locate/measurement

Conductivity of surface modified TiO2 dope nanocomposites S.C. Nagaraju a,b, Aashis S. Roy c, G. Ramgopal d,⇑ a

Department of Physics, Bharathiar University, Coimbatore, Tamil Nadu, India Department of Physics, Vidyavahini College, SIT Extn., Tumkur, Karnataka, India Horizon School, Sindhanur, Raichur, Karnataka, India d Department of Physics, Maharani’s Science College, Palace Road., Bangalore, Karnataka, India b c

a r t i c l e

i n f o

Article history: Received 11 July 2014 Received in revised form 19 September 2014 Accepted 3 October 2014 Available online 23 October 2014 Keywords: Polymer–matrix composites (PMCs) Electrical properties Surface properties Electron microscopy

a b s t r a c t Dielectric properties of TiO2 nanoparticles doped O-chloropolyaniline nanocomposites have been prepared using Camphorsulfonic acid. The prepared composites were characterized by FTIR for structural studies, SEM and TEM for surface morphology. The characteristic peaks of benzeniod ring, quiniod ring and MAO bending confirm the formation of nanocomposites. TEM image shows that the TiO2 nanoparticles are about 10 nm embedded in OPANI. Among all composites, 15 wt.% of nanocomposites shows high DC conductivity 4  103 S/cm compare to other compositions. The dielectric constant decreases as a function of applied frequency due to the multiple polarizations occur in polymer nanocomposites. Among all composites 15 wt.% of O-chloropolyaniline/TiO2 nanocomposite shows low dielectric constant and high AC conductivity of 3  104 S/cm. Tangent losses of these very low that is 2.5 X and it almost constant after 105 Hz hence these materials would be great importance in low k-dielectric application. Therefore these composites are suitable for electronic applications. Ó 2014 Elsevier Ltd. All rights reserved.

1. Introduction Conducting polymer has become an interesting field for scientific community because of its wide applications in engineering and technology. The designing of new supramolecules with the desired structure and properties for different application has attracted in recent years [1]. These conducting polymers got more attention because of its easily tunable electrical property by incorporating filler materials to in it [2]. Among all conducting polymers, polyaniline is extensively studied because of its easy synthesis, low cost, environmental stability and tunable electrical property by adding small quantity of inorganic or organic materials [3]. The nano-dimension fillers incorporated into the matrix changes tremendously, its electrical properties due to the ⇑ Corresponding author. Tel.: +91 8022 262796. E-mail address: [email protected] (G. Ramgopal). http://dx.doi.org/10.1016/j.measurement.2014.10.012 0263-2241/Ó 2014 Elsevier Ltd. All rights reserved.

high surface energy, homogeneous distribution and proper orientation of nanoparticles results isotropy throughout the matrix [4]. However the composite property also depends on the way of preparation, reaction mechanism, matrix composition and filler concentration. One of the co-authors earlier reported AC conductivity of polyaniline–n-TiO2 composites and found that the rAC conductivity greatly influenced by nanoparticles due to the nanodimension and orientation of nanoparticles in polyaniline matrix [5]. It is observed that the substituted polyaniline shows high conductivity because the p-electron of benzene ring delocalize cause resonant for longer time and hence conductivity is higher than polyaniline [6,7]. Lakshmi et al. reported that preparation of OPANI–NiTiO3 composites and found that the NiTiO3 influence the conductivity up to 0.3  102 S/cm and the tangent losses is about 10 at 105 Hz [8]. In this connection we made an effort to improve the conductivity of Ortho-chloropolyaniline (OPANI) by adding TiO2 nanoparticles using camphor

S.C. Nagaraju et al. / Measurement 60 (2015) 214–221

sulphonic acid as surfactant which will be improve the interface and avoid the agglomeration becomes easy in the electron transport mechanism. The prepared composites were characterized by Fourier transform infrared (FTIR) spectroscopy, Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). Further the DC and AC properties were studied by Kelvin two probe methods using Hioki LCR meter in the range of 50–5 MHz.

215

and Ortho-chloropolyaniline–TiO2 nanocomposites are washed with 300 ml of 0.2 M sulphuric acid to remove the unreacted monomer, followed with distilled water and acetone to remove SO 4 ions and excess APS from OPANI–TiO2 nanocomposites. Further, the nanocomposites precipitate is dried under vacuum to achieve a constant weight [10]. 2.4. Characterization and experimental techniques

2. Experimental 2.1. Materials and method The monomer Ortho-chloroaniline, Ammonium persulphate (APS) ((NH4)2S2O8), sulphuric acid (H2SO4) (AR grade), Camphorsulfonic acid, TiO2 nanoparticles (99.999% purity) and acetone were procured from Sigma– Aldrich, India. All chemicals were of analytical reagent (AR) grade and were used as received without any further purification. 2.2. Synthesis of Ortho-chloroaniline The 500 ml volumetric flask containing 1 M solution of Ortho-chloroaniline (100 ml) and 1 M sulphuric acid which acts as proton donor were dissolved in distilled water in equimolar ratio and stirred for 20 min to get Ortho-chloroaniline sulphuric acid solution. To the above mixture 10 ml surfactant of 0.1 M Camphorsulfonic acid is added and then to which oxidizer is added 0.25 M Ammonium persulphate of 100 ml solution to the above solution slowly drop by drop at the rate of 5 ml per minute and the resulting solution is stirred for an hour at 0–5 °C temperature using magnetic stirrer. The reaction mixture is allowed to keep for 24 h to complete the polymerization of monomers and get better yield without formation of oligomers. Next day, the reaction mixture is filtered using vacuum pump and Ortho-chloropolyaniline (OPANI) precipitate is washed with 300 ml of 0.2 M sulphuric acid to remove the unreacted monomer, followed with distilled water and acetone to remove SO 4 ions and excess APS from Ortho-chloropolyaniline. Further, the Ortho-chloropolyaniline precipitate is dried under vacuum to achieve a constant weight [8,9]. 2.3. Synthesis of Ortho-chloroaniline–TiO2 nanocomposites 1 M solution of O-chloroaniline (100 ml) and 100 ml of 1 M sulphuric acid are dissolved in double distilled water and TiO2 nanoparticles in various weight percentage (05, 10, 15, 20 and 25 wt.%) and stirred for 40 min and form Ortho-chloroaniline sulphuric acid solution which contains homogenously distributed suspended TiO2 nanoparticles. To the above mixture 10 ml of 0.1 M Camphorsulfonic acid is added and then to which 0.25 M Ammonium persulphate of 100 ml solution is added drop by drop slowly to the above at the rate of 5 ml per minute and the resulting solution is stirred for an hour at 0–5 °C temperature using magnetic stirrer. The reaction mixture is left in the ice bath for 24 h to complete polymerization of monomers. Next day, the reaction mixture is filtered using vacuum pump

The Fourier transform infrared spectra of the samples were recorded on a Perkin Elmer 1600 spectrophotometer in KBr medium (sample to KBr ratio is 1:5) in the wave number range 400–4600 cm1. The surface morphology of Ortho-chloropolyaniline and its composites in the form of pellets was investigated using Philips XL 30 ESEM scanning electron microscope on Au substrate. The transmission electron microscopy (TEM) image of the sample was obtained using JEOL Model 1200KVEX instrument operated at 120 kV. Sample for TEM analysis was prepared by dispersed the O-chloropolyaniline and its nanocomposites on carbon-coated copper grids, has been kept for 5 min. The samples on the TEM grid is exposed to IR light for 30 min for drying. The DC conductivity was studied by preparing pellets of 10 mm diameter with thickness varying up to 2 mm by applying pressure of 10 Tons in a UTM–40 (40 Ton Universal testing machine). For temperature dependent conductivity and sensor studies, the pellets are coated with silver paste on either side of the surfaces to obtain better contacts. The DC measurement was carried by two probe method and the change in resistance is measured using Keithley meter. Frequency-dependent electrical conductivity was measured by two probe technique using laboratory made setup. The dielectric tangent loss and dielectric constant are studied by sandwiching the pellets of these composites between the silver electrodes in the frequency range of 50–5 MHz using the Hioki LCR Q meter. 3. Results and discussion 3.1. Fourier transform infrared spectroscopy The molecular structure is carried out by Fourier transform infrared spectroscopy (FTIR) for TiO2 nanoparticle doped O-chloropolyaniline nanocomposites with different weight percentages. Fig. 1(a) shows the FTIR spectra of pure O-chloropolyaniline and is observed that characteristic peaks around 2922 cm1 corresponds to CAH stretching of aromatic ring, 1566 cm1 is due to the [email protected] stretching vibration of quinoid ring, 1493 cm1 for stretching vibration of benzenoid ring, 1406 cm1 is the characteristic mode of vibration of CAH bonding of aromatic nuclei, 1302 cm1 assigned for the stretching of CAN bonds of aromatic amine, 1142 cm1 is one of the important peaks assigned for measure of degree of delocalization of electron in aromatic ring, 796 cm1 corresponds to NAH rocking vibration mode out of the plain, 592 cm1 and 472 cm1 are due to the bonding of CAH in aromatic ring out of the plain respectively [11–13].

216

S.C. Nagaraju et al. / Measurement 60 (2015) 214–221

in the concentration of TiO2 nanoparticles. From the SEM images it is observed that nano-oxides are embedded layer by layer and developed small leaf one over the other. Uniform morphology obtained is due to no polymer chain entanglement during polymerization process. The SEM images of OPANI–TiO2 nanocomposites show the layered structure with layer thicknesses around 2 to 3 microns. 3.3. Transmission electron microscope Fig. 3 shows transmission electron micrograph (TEM) of pure TiO2 nanoparticles (Fig. 3a) and OPANI/TiO2 nanocomposite (Fig. 3b). The pure TiO2 nanoparticles (fig. 3(a)) are homogeneous individual particles form spherical in size and while this agglomerated in OPANI/TiO2 nanocomposite increasing considerably. Fig. 3(b) presents that OPANI/TiO2 nanocomposite possesses an embedded structure. Therefore, an embedded structure has been formed by the in situ polymerization of O-chloroaniline on the surface of TiO2 nanoparticles. Fig. 1. (a–f) FTIR spectra of O-chloropolyaniline and O-chloropolyaniline/ TiO2 nanocomposites.

Fig. 1(b–f) shows the FTIR spectra of O-chloropolyaniline/TiO2 nanocomposite. The important characteristic peaks are observed around 1596–1556 cm1 corresponds to the [email protected] stretching vibration of quinoid ring, 1487– 1484 cm1 assigned for stretching vibration of benzenoid ring, 1305–1302 cm1 are due to the stretching of CAN bonds of aromatic amine, 1145–1140 cm1 for measuring of degree of delocalization of electron in aromatic ring, 864–738 cm1 for NAH of vibration of rocking mode, 613–584 cm1 corresponds to vibration of TiAO in the plain and 509–497 cm1 for the bonding of CAH bonding in aromatic ring out of the plain respectively [14]. 3.2. Scanning electron microscope Scanning electron microscope (SEM) is used to investigate the surface morphology of OPANI and OPANI–TiO2 nanocomposites and to evaluate the effect of presence of TiO2 nanoparticles on the structure of OPANI for different weight percentages. Fig. 2(a) shows the SEM image of pure OPANI. The surface of OPANI shows a specific pattern of spikes like structure. It is observed that the grains are agglomerated and are spindle in shape representing a flower like structures. The average grain size is found to be about 200 lm. Fig. 2(b–f) shows the SEM image of 5, 10, 15, 20 and 25 wt.% of OPANI–TiO2 nanocomposite. It exhibits a layered and wrinkled leaf like structure, representing a curled and corrugated morphology intrinsically associated with TiO2 nanoparticles. However, surface morphology of OPANI–TiO2 nanocomposites is totally changed into flaky for the above 10 wt.% nanocomposites. Further it is observed that the increase in weight percentage of oxide nanoparticles transition from flake to spherical like layered morphology [15]. The formation of layers in the nanocomposite structure has been increased with increase

3.4. DC conductivity The variation of DC conductivity with different temperature of OPANI/TiO2 nanocomposites with different weight percentage is as shown in Fig. 4a. It is observed that the conductivity of all weight percentages of OPANI/TiO2 nanocomposites increases with increase in temperature. The three steps of conductivity were observed in these characteristics of semiconducting materials. The conductivity was measured in a temperature range in a step wise from 30 °C to 220 °C. Initially the conductivity is almost constant up to 110 °C afterwards it gradually increases till the temperature reaches to 150 °C and then suddenly increases up to 220 °C. Among all composites and pure OPANI, the 15 wt.% of TiO2 doped OPANI nanocomposites show high conductivity of 0.004 S/cm. This may be due to decrease in distance between the entangled polymer chains and TiO2, which helps in the tunneling of the electron from one site to another one easily. This is confirmed from the negative thermal coefficient (NTC) (a) in Fig. 4b. It is clearly found that the a value increases with increase in concentration of the TiO2 in OPANI matrix indicates that the thermal resistance of the matrix enhances due to the strong bonding between TiO2 nanoparticles and matrix [16] The negative coefficient value shows that these materials act as semiconductor at higher temperature [17]. When the temperature rises up, the average amplitude of the atoms vibration within the matrix increases. This, in turn increases the separation between the TiO2 atoms causing the OPANI polymer expands, which increases the conduction path network in nanocomposites. It is believed that the material does not undergo any phase change, so that the expansion can be easily related to the temperature change. It is also known that the thermal expansion will cause significant stress in the nanocomposite matrix and does not allow for expansion and contraction of matrix which increases the electron density in the junction and cause blocking of charge carriers [18]. However in this case, it is understood from the thermal coefficient graph, there is an expansion of the matrix with the increase in

S.C. Nagaraju et al. / Measurement 60 (2015) 214–221

217

Fig. 2. (a–f) SEM image of O-chloropolyaniline and O-chloropolyaniline/TiO2 nanocomposites.

temperature causes increase in the conduction path as a results the conductivity of the nanocomposites also increases. 3.5. Dielectric studies Variation of real part of permittivity (e0 ) as a function of frequency for OPANI and for various weight percentages of TiO2 in OPANI nanocomposites is shown in Fig. 5. It is observed that, in all these composites the dielectric constant is high at low frequencies and also the value is high for higher weight percentage of TiO2 in polymer matrix and sharply decreases with increase in applied frequency and almost becomes constant for

frequencies greater than 103 Hz for all the cases. High values of permittivity at lower frequency range are due to maximum accumulated charge carriers at the interface of grain boundaries. The strong frequency dispersion of permittivity is observed in the low frequency region [19]. The observed behavior may be due to dipole polarization along with Maxwell–Wagner–Sillars (MWS) polarization [20] at the interface of electrode and nanocomposites surface taking place in these materials lead to a large dispersion throughout the frequency range. The interaction between OPANI chains and surface of TiO2 nanoparticles restricts the motion of dipoles which leads to decrease of e0 at higher frequencies. Among all composites it is observed that 15 wt.% of OPA-

S.C. Nagaraju et al. / Measurement 60 (2015) 214–221

Negative thermal coefficient (α)

218

-1.6 -1.8 -2.0 -2.2 -2.4 -2.6 -2.8 -3.0 0

5

10

15

20

25

Concentration X Fig. 4b. NTC behavior of O-chloropolyaniline/TiO2 nanocomposites for various wt.%.

OPANI 05 wt% 10 wt% 15 wt% 20 wt% 25 wt%

Relative permitivity ( ε')

1000

800

600

400

200 2

10

Fig. 3. (a, b) TEM image of O-chloropolyaniline and O-chloropolyaniline/ TiO2 nanocomposites.

σ dc S/cm

0.003

4

10

5

10

6

10

Frequency (Hz) Fig. 5. Relative permittivity of O-chloropolyaniline/TiO2 nanocomposites as a function of applied frequency.

OPANI 5 wt% 10 wt% 15 wt% 20 wt% 25 wt%

0.004

3

10

OPANI 05 wt% 10 wt% 15 wt% 20 wt% 25 wt%

1200

0.002 1000

ε''

0.001

800 0.000 0

50

100

150

200

250

400

Temperature in ( 0C) 2

Fig. 4a. DC conductivity of O-chloropolyaniline/TiO2 nanocomposites against temperature.

NI–TiO2 nanocomposite show low relative permittivity value of 433 F/m compared to other composites. Fig. 6 shows the variation of imaginary part of permittivity (e00 ) with frequency for different weight percentage of TiO2 in OPANI at room temperature. The imaginary part

10

3

10

4

10

5

10

6

10

Frequency (Hz) Fig. 6. Imaginary permittivity of O-chloropolyaniline/TiO2 nanocomposites as a function of applied frequency.

of permittivity also has a similar nature as that of real part of permittivity with frequency and becomes almost constant beyond 103 Hz but the magnitude of the imaginary

219

S.C. Nagaraju et al. / Measurement 60 (2015) 214–221

Quality factor (Q)

0.25

OPANI 05 wt % 10 wt % 15 wt % 20 wt % 25 wt %

0.20 0.15 0.10 0.05 0.00 1

10

2

10

3

4

5

10 10 10 Frequency (Hz)

6

10

Fig. 7. Quality factor of O-chloropolyaniline/TiO2 nanocomposites.

OPANI 05 wt% 10 wt% 15 wt% 20 wt% 25 wt%

35000 30000 25000

Z'

20000 15000 10000 5000 0 -5000 2

10

3

10

4

5

10

10

6

10

Frequency (Hz) Fig. 8. Real part of Impedance of O-chloropolyaniline/TiO2 nanocomposites against applied frequency.

3.0 2.5 2.0

tanδ

part of permittivity is higher than that of e0 . At room temperature, the value of e00 is high for higher weight percentage of dopant in matrix and decreases with increase in applied frequency for all the composites. This is also due to dipole polarization i.e. due to rotation of dipoles between two equivalent equilibrium positions and MWS polarization causes large scattering of charge carrier’s results high dispersion [21,22]. It is the spontaneous alignment of dipoles in one of the equilibrium position that gives rise to nonlinear polarization behavior in these composites. The variation of quality factor (Q) as a function of frequency is shown in Fig. 7 for various weight percentages of OPANI–TiO2 nanocomposites. It is observed that the Q values change linearly for all the cases with applied frequencies as well as with the increasing filler concentration. However, after 103 Hz, it linearly increased and reached maximum in between 103 and 104 Hz. Further, it gradually decreased around 106 Hz and remains constant thereafter. Q value is found to be less than 0.04 due to over damping, reflecting the fact that the charge carriers does not oscillate at all. At equilibrium, a hump is formed due to the steady state of electron flow through the polymer composites asymptotically [23,24]. Among all the nanocomposites, 15 wt.% shows the high Q value of 0.25 is followed by other nanocomposites and pure polymer. The real part of impedance (Z0 ) against frequency is shown in Fig. 8. It is observed that the impedance value decreases with increase in frequency. The variation of impedance value depends on filler concentration in OPANI–TiO2 nanocomposite matrix. Three different processes occur in the multiphase composite system: association of charge carriers, dielectric dispersion because of different dipole rotation and the presence of both dielectric dispersion as well as charge carriers union within measured frequency range. The presence of relaxation peaks in both the complex impedances at low frequencies with increase in temperature could be due to space-charge relaxation [26] below 1 kHz. Therefore, electrical resistance decreases with decrease in complex impedance. Fig. 9 shows the variation of tan d as a function of frequency for various weight percentages of TiO2 in OPANI. It is observed that the dielectric loss decreases with

1.5 1.0

OPANI 05 wt% 10 wt% 15 wt% 20 wt% 25 wt%

0.5 0.0

2

10

3

10

4

10

5

10

6

10

Frequency (Hz) Fig. 9. Tangent loss of O-chloropolyaniline/TiO2 nanocomposites.

increase in applied frequencies. These energy losses are very small after 103 Hz. The constant tangent loss value at the lower frequency indicates that there should be two types of relaxation processes. Further increasing the frequency above 104 Hz, reduces the dielectric loss completely. Among all the composites, 15 wt.% shows low dielectric loss of 2.5 X compared to other nanocomposites [25]. Therefore, these materials can be used as low kdielectric material in electronic transistors, microelectronic devices, etc. The Cole–Cole graphs indicate a decrease in electrical resistance with increasing filler concentration as well as with the applied frequency, as shown in Fig. 10. The impedance value depends on the bulk resistance and grain resistance in a complex LCR circuit. The bulk resistance and grain resistance is noticed that it decreases with increase in TiO2 concentration and as a result the impedance value also decreases. It is observed that as the filler concentration increases, area under the curve decreases up to percolation threshold, indicating a sharp drop in the resistance. The formation of semicircular arc indicates that the presence of two different components in the composites form a series resistor and geometrical capacitance and a

220

S.C. Nagaraju et al. / Measurement 60 (2015) 214–221

10000

OPANI 05 wt% 10 wt% 15 wt% 20 wt% 25 wt%

Z''

-1

6000

σac S/cm x (10 )

8000

4000 2000

1

10

2

10

3

10

4

10

5

10

6

10

1

7

Z'

decrease in the arc area indicates increase in the bulk conductivity as shown in inset figure. The formation of two semicircles is observed and it shows that relaxation time decreases with increase in applied frequency till 15 wt.% and increases thereafter, which might be due to increase in grain resistance. The variation of relaxation time against different weight percentage of TiO2 in OPANI nanocomposites are shown in Fig. 11, which is calculated from Cole–Cole plots by using the formula [27].

T ¼ 0:5pf c where fc is maximum peak position of Cole–Cole plot in particular frequency range. The analysis of Cole–Cole plots suggests that there is an increase in the relaxation time distribution for higher percentage of TiO2 nanoparticles in polymer matrix. It is observed that relaxation time varies with increase in filler concentration in the polymer matrix. Among all the composites, 15 wt.% shows low relaxation time indicating that the flow of charge carriers is faster than other composites and it may be due to low bulk resistance and less grain boundaries. The formation of low grain boundaries supports easy hopping and

3.0

2.5

2.0

1.5

1.0 0

5

10

2

10

3

10

4

10

5

10

6

10

Frequency (Hz)

Fig. 10. Cole–Cole plot of O-chloropolyaniline/TiO2 nanocomposites.

Relaxation time (τ)

2

0

0

10

OPANI 05 wt% 10 wt% 15 wt% 20 wt% 25 wt%

3

15

20

25

wt% of n-TiO2 in OPANI Fig. 11. Relaxation time against various wt.% of O-chloropolyaniline/TiO2 nanocomposites.

Fig. 12. AC conductivity of O-chloropolyaniline/TiO2 nanocomposites as a function of applied frequency.

tunneling of polarons and bipolarons from one island to another. The variation of AC conductivity of OPANI–TiO2 nanocomposites as a function of applied frequency is shown in Fig. 12. It is observed that AC conductivity increases with increase in frequency. Among all the composites, 15 wt.% showed a high conductivity of 3  104 S/cm, which is due to its low electrical resistance and low dielectric constant value. Above 15 wt.% loadings, all other compositions showed lower conductivity due to predominant dipole polarization which increases the value of dielectric constant.

4. Conclusion The titanium dioxide nanoparticles doped O-chloropolyaniline nanocomposites have been prepared via in situ polymerization using Camphorsulfonic acid as surfactant. Structural characterization have been carried out by FTIR spectroscopy and important peaks of metal oxide and polymers are appeared in the spectra confirm the formation of nanocomposites. The surface morphology has been studied by using scanning electron microscopy and observed that the nanoparticles are homogeneously disturbed in the nanocomposite matrix. The nanoparticles help the composite nucleation in two dimensions as a result a flake like structure is formed. Further the DC conductivity has been studied by using Kelvin two prove method and found that the conductivity increases with increase in temperature. The three steps conductivity confirms that the hooping is the major conduction mechanism in these nanocomposites. Among all nanocomposite 15 wt.% shows high DC conductivity of 0.004 S/cm. Dielectric studies reveals that the permittivity value decreases with increase in applied frequency as well as the filler concentration up to 15 wt.% and thereafter the permittivity value increases because of the formation of permanent dipole in the nanocomposites. The tangent loss graphs show that the above 103 Hz there is no loss of energy therefore these materials can be used as low k-dielectric materials. AC conductivity show that among all nanocomposites, 15 wt.% of O-PANI/ TiO2 nano-

S.C. Nagaraju et al. / Measurement 60 (2015) 214–221

composites shows high conductivity of 3  104 S/cm and followed by the other nanocomposite composition. Therefore these nanocomposites are more suitable for engineering electronic applications. References [1] Aashis S. Roy, A. Parveen, Raghunandan Deshpande, Ravishankar Bhat, K.R. Anilkumar, J. Nanopart. Res. 15 (2013) [14:1337]. [2] J.L. Wojkiewicz, S. Fauveaux, J.L. Miane, Synth. Met. 135 (2003) 127– 128. [3] T. Maeda, S. Sugimoto, T. Kagotani, N. Tezuka, K. Inomata, J. Magn. Magn. Mater. 281 (2004) 195. [4] S. Koul, R. Chandra, S.K. Dhawan, Sens. Actuat. B Chem. 75 (2001) 151. [5] Aashis S. Roy, Satyajit Gupta, S. Sindhu, Ameena Parveen, Praveen C. Ramamurthy, Compos. B Eng. 47 (2013) 314. [6] Aashis.S. Roy, Ameena Parveen, M.V.N. Ambika Prasad, Koppalkar R. Anilkumar, Emerald: Sens. Rev. 32 (2013) 163–169. [7] W. Xue, K. Fang, H. Qiu, J. Li, W. Mao, Synth. Met. 156 (2006) 506. [8] Mohana Lakshmi, Aashish S. Roy, Syed Khasim, Muhammad Faisal, K.C. Sajjan, M. Revanasiddappa, AIP Adv. 3 (2013) 112113. [9] A. Parveen, A. koppalkar, A.S. Roy, Sens. Lett. 11 (2013) 242–248. [10] S.K. Dhawan, N. Singh, D. Rodrigues, Sci. Technol. Adv. Mater. 4 (2003) 105–113. [11] Ameena Parveen, Aashis S. Roy, J. Mater. Res. 28 (2013) 840. [12] D. Rajendra, A.S. Roy, A. Parveen, Compos. B Eng. 52 (2013) 211–216. [13] P. Singjai, A. Wongjamras, L.D. Yu, T. Tunkasiri, Chem. Phys. Lett. 366 (2002) 51–55. [14] Ramesh Patil, A.S. Roy, K.R. Anilkumar, K.M. Jadhav, S. Ekhelikar, Compos. B Eng. 43 (2012) 3406–3411.

221

[15] V. Senthil, T. Badapanda, S.N. Kumar, P. Kumar, S. Panigrahi, J. Polym. Res. 19 (2012) 9838. [16] G.S. Yashavanth Kumar, H.S. Bhojya Naik, Aashis S. Roy, K.N. Harish, R. Viswanath, Nanosci. Nanotechnol. 2 (2012) 1–6. [17] J. Luo, H.G. Huang, H.P. Zhang, L.L. Wu, Z.H. Lin, M. Hepel, J. New Mater. Electrochem. Syst. 3 (2000) 249–252. [18] H. Kunteppa, Aashis S. Roy, H. Devendrappa, M.V.N. Ambika Prasad, J. Appl. Polym. Sci. 125 (2012). [19] Ameena Parveen, Koppalkar R. Anilkumar, Aashis S. Roy, IEEE Sens. J. 12 (2012) 2817–2823. [20] R.P. McCall, J.M. Grinder, J.M. Leng, Phys. Rev. B 41 (1990) 5202– 5213. [21] Aashis S. Roy, K.R. Anilkumar, M.V.N. Ambika Prasad, Core–Shell method of J. Appl. Poly. Sci. 121 (2011) 675. [22] P. Indra Devi, K. Ramachandran, J. Exp. Nanosci. 6 (2011) 281–293. [23] K. Wakabayashi, M. Fujita, H. Ajiki, M. Sigrist, Physica B 280 (2000) 388–389. [24] Aashis S. Roy, K.R. Anilkumar, M.V.N. Ambika Prasad, J. Appl. Poly. Sci. 123 (2012) 1928–1934. [25] S.L. Patil, S.G. Pawar, M.A. Chougule, B.T. Raut, P.R. Godse, S. Sen, V.B. Patil, Int. J. Polym. Mater. 61 (2012) 809–820. [26] E.M.C. Fortunato, P.M.C. Barquinha, A.C.M.B.G. Pi-mentel, A.M.F. Goncalves, A.J.S. Marques, L.M.N. Pereira, Adv. Mater. 17 (2005) 590. [27] L.I. Qingshan, G.A.O. Wenjie, M.A. Pengsheng, Adv. Nat. Sci. 1 (2008) 81–88.

Further reading [28] G. Chakraborty, K. Gupta, A.K. Meikap, R. Babu, W.J. Blau, J. Appl. Phys. 109 (2011) 033707.