temperature dependent electrical conductivity of polyaniline/y2o3 composites

ISSN 0965�545X, Polymer Science, Ser. A, 2013, Vol. 55, No. 9, pp. 549–555. © Pleiades Publishing, Ltd., 2013.

549

1 INTRODUCTION

Intrinsically conducting polymers in general, andpolyaniline (PANI) in particular, are an interestingclass of materials as they offer chemical stability,ease of synthesis [1] and low cost compared withinorganic semiconductors. These polymers havewide applications such as in solar cells, lightweightbatteries, light emitting diodes, polymer corrosionprotection agents, sensors and molecular electronicdevices. Conducting polymer/inorganic nanoparti�cles composites have attracted considerable atten�tion because of their novel physical and chemicalproperties and potential applications. These com�posite systems can provide new synergistic proper�ties that cannot be attained from individual materi�als [2–6], such that the conductivity is more easilycontrolled, and the mechanical or thermal stabilityis improved through the synthesis of the nanocom�posites [7]. In recent years, the development of inor�ganic/polymer hybrid materials on nanometer scalehave been receiving significant attention due to awide range of potential applications in optoelec�tronic devices [8–10] and in field effect transistors[11]. The inorganic fillers at nanoscale exhibit high‘surface to volume ratio’ and thus expected to mod�ify drastically the electrical, optical and dielectricproperties of the polymer. In general, the synthesisof hybrid of polymer/inorganic material has the goalof obtaining a new composite material having syner�getic or complementary behaviors between the poly�mer and inorganic material. Of conducting poly�

1 The article is published in the original.

mers, polyaniline (PANI) is generally recognized tobe one of promising conducting polymers for com�mercial application due to its high electrical con�ductivity, good environmental stability and ease ofsynthesis [12]. Until now, various composites ofPANI with inorganic nanoparticles have been syn�thesized either by an electrochemical or by a chem�ical oxidative polymerization [13–16]. Amongthem, Y2O3 nanoparticles have been intensivelystudied because of their good thermal stability, aswell as their wide applications in host matrices ofphosphors [17], catalyst support or even catalysts[18], and dielectric insulators of electroluminescentdevices [19]. Although there are lots of papers aboutPANI/inorganic nanoparticles composites, no studydealing with PANI /nano�Y2O3 composites has beenreported so far. Combination of rare earth oxidenanoparticles with semiconducting PANI may offercomposites with unique properties. In this study, wereport chemical synthesis of PANI with nano�Y2O3

composite. The structural properties and tempera�ture dependent DC electrical conductivity of com�posite were investigated. Temperature DependenceDC Electrical Conductivity of PANI with differentratio of Y2O3 at different temperatures has beenstudied. The results cover direct current (dc) electri�cal conductivity Temperature dependant, Activationenergy, hopping length were calculated, and dis�cussed the obtained results. Variable range hopping(VRH) gives the charge transport mechanism inmaterial and is useful in fabricated of electronicsdevices.

Temperature Dependent Electrical Conductivityof Polyaniline/Y2O3 Composites1

Muhammad Saeed, Abdul Shakoor, and Ejaz AhmadDepartment of Physics, Bahauddin Zakariya University, Multan, 60800 Pakistan

e�mail: [email protected] October 1, 2012;

Revised Manuscript Received December 24, 2012

Abstract—Composites of polyaniline with yttrium oxide (Y2O3) nanoparticles have been prepared by chem�ical polymerizations method by increasing the weight percentage of yttrium oxide. X�Ray diffraction (XRD)and Fourier Transform Infrared Spectra (FTIR) were used to characterize the composites. XRD and FTIRpattern indicate that Polyaniline (PANI) is intercalated into the layers of Y2O3 nanoparticles successfully byin situ polymerization and therefore the degree of crystallinity increases due to crystalline of yttrium oxidenanoparticles. The scanning electron micrographs (SEM) also confirm the formation of dual phase of plateletas well as of flaky structure in PANI–Y2O3. Temperature dependant DC conductivity showed three dimen�sional variable ranges hopping (3D VRH) model. Activation energy, density of states and hopping length arecalculated and found to be influenced by intercalating PANI into the layers of Y2O3 clay.

DOI: 10.1134/S0965545X13080105

COMPOSITES

550

POLYMER SCIENCE Series A Vol. 55 No. 9 2013

MUHAMMAD SAEED et al.

EXPERIMENTAL

Materials

Aniline (Merck) was distilled under reduced pres�sure and stored at low temperature prior to use.Ammonium per sulfate (APS) was obtained fromSigma Aldrich. Yttrium oxide was supplied by SigmaAldrich and used as obtained. All materials were usedas provided without any further.

Synthesis of Polyaniline (PANI)

Aniline was added dope wise in 30 mL distilledwater for about 1h and the solution was left stirring for6 h. HCl was added dope wise in it to keep PH between0 and 1. After this Ammonium per sulphate (APS) wasadded drop wise for about 30 minutes period, whereasmolar ratio of oxidant to monomer was kept 1/2. Asthe Ammonium per sulphate (APS) mixed with thesolution, it turned to greenish black color, indicatingthat the organic polymerization reaction has begun.The solution was left overnight, the next day the solu�

tion was filtered and a dark black�green paste of Poly�aniline was obtained which was washed with plenty ofdistilled water until the filtrate become colorless. Thepaste was kept at 60°C in a vacuum oven for 24 h.

Synthesis of PANI/Y2O3 Composites

Yttrium oxide mixed in 100 mL distilled water andthe mixture was stirred for about 1h in order to dis�perse Y2O3 in the solution. Aniline was added dopewise for about 1h and the solution was left stirring for6 h. HCl was added in it to keep PH between 0 and 1.After this, Ammonium per sulphate (APS) was addeddrop wise for about 30 minutes period and Y2O3 wasvaried from 5% to 35%, whereas molar ratio of oxidantto monomer was kept 1 : 2. As the Ammonium per sul�phate (APS) mixed with the solution, it turned togreenish black color, indicating that the organic poly�merization reaction has begun. The solution was leftovernight, the next day the solution was filtered and adark black�green paste of Polyaniline–Y2O3 wasobtained which was washed with plenty of distilledwater until the filtrate become colorless. The paste waskept at 60°C in a vacuum oven for 24 h.

Measurements

DC conductivity was measured in pressed pellets ina press machine at 10 ton pressure in stainless steel dieof 3 mm diameter and 1 mm thickness by using a two�point method at temperature range from 293 to 403 K.The samples were connected to a Keithley 2400 elec�trometers and a current source electrometer. The tem�perature was controlled by cryostat and measured bydigital bimetallic thermometer. The conductivity of allthe samples and reproducibility were checked. X rayspowder diffraction analysis was carried out using anautomated diffractometer, Panalytical X’ Pert PROequipped with CuK

α radiations (λ = 1.54 Å). The

instrument was operated at 40 kV and 30 mA and dif�fraction patterns of PANI and PANI–Y2O3 Compos�ites samples mounted on a standard holder wererecorded over the range of 10 to 70° counting time was0.5 s and the step size was 0.02. The FTIR spectra wasrecorded on KBr pellet samples in the range of 4000–500 cm–1 by using a Perkin–Elmer Fourier transformInfra red spectrometer. Scanning electron microscopywas carried out on an EVO50 ZEISS instrument.

RESULTS AND DISCUSSION

XRD Analysis

Figure 1 shows the XRD patterns of pure Y2O3

nanoparticles. The XRD pattern of the Y2O3 nanopar�ticles is in good accordance with that on the JCPDcard S25–1200, which reveals that the sample hascubic crystal system having space group I213 anddegree of crystalline are summarized in Tables 1 and 2.

20

Intensity, a.u.

2θ, deg

2000

3000

1000

0806040

(211)

(222)

(400)

(440)

(622)

(622)

Fig. 1. XRD Pattern of pure Y2O3.

Table 1. X�ray diffraction data for Y2O3

2θ, deg d�spacing, nm (khl)

20.49 0.433 211

29.14 0.306 222

33.76 0.265 400

48.51 0.187 440

57.57 0.159 622


TEMPERATURE DEPENDENT ELECTRICAL CONDUCTIVITY 551

It has been reported that the crystallinity of poly�mers depends on the condition set during the synthesisof the polymer [20]. X�ray diffraction patterns of thepolyaniline exhibits no sharp peak except a broad peakin the range of 18–28°, (Fig. 2, curve 1) which is char�acteristic peak of PANI and suggests that the structureof pure polyaniline is amorphous as reported in the lit�erature [21].

The pattern of amorphous broad peak (18–28°) inPANI is present in all PANI–Y2O3 compositesaccording to its proportion. It is obvious that the dif�fraction peaks of the PANI–Y2O3 composites shifts tolower 2θ values as compared with pristine Y2O3, Whichindicates the successful intercalation of PANI in to thenano�inter lamellar spaces of Y2O3 clay. From X raysdiffraction intensity versus 2θ it is observed clearly thatthe amorphous nature of polyaniline is decreasing andcrystallinity is increasing. The experimental d�valuesare calculated by using Bragg’s relation [22]. In Fig. 2(curve 4) four sharp crystalline peaks of PANI–Y2O3

at 2θ values of 18.77, 25.47, 42.02 and 48.94° corre�sponds to the periodicity d = 0.472, 0.349, 0.023,0.047 nm. Thus these sharp peaks are clearly showingthat after inserting Y2O3 in PANI crystallinity isincreased [23].

FTIR Spectra

Figure 3 shows the FTIR spectra of pure PANI,Nano–Y2O3 particles and of two types of composite.The spectra of the composites (curves 3 and 4) clearly

feature characteristic absorption peaks ofPANI/nano–Y2O3. The band at 1590 cm–1 corre�sponds to the C–C and C=C stretching vibrations andthat at 1494 cm–1 can be ascribed to the C–N stretch�ing vibration. The broad band from 1400 to 1250 cm–1

is attributed to C–H or C–N in�plane deformationmodes and has a maximum at 1292 cm–1.The aboveresults indicate the formation of PANI in the compos�ite. From Fig. 3, remarkable differences betweenPANI/nano–Y2O3 composite and pure PANI becomeapparent. The characteristic peaks of the PANI mole�cules in the composite are shifted to lower wave num�bers compared with those of pure PANI. From this, itmay reasonably be concluded that there is a stronginteraction between PANI and the Y2O3 nanoparti�cles. The addition of Y2O3 nanoparticles probablyresults in the formation of hydrogen bonding between

Table 2. X�ray diffraction data for PANI–Y2O3 composites

2θ, deg d�spacing, nm (khl)

18.77 0.472 211

25.47 0.349 222

42.02 0.023 440

48.94 0.047 622

10

Intensity, a.u.

2θ, deg705030

4

3

2

1

Fig. 2. XRD Pattern of (1) synthesis PANI, (2) PANI/Y2O3composite (10% Y2O3) (3) PANI/Y2O3 composite (25%Y2O3), and (4) PANI/Y2O3 composite (35% Y2O3).

4000

Relative absorption

Wavenumber, cm−1100020003000

4

3

2

1

Fig. 3. FTIR spectra of (1) pure PANI, (2) Y2O3 nano�par�ticles, (3) PANI/Y2O3 composite (25% nanoparticles), (4)PANI/Y2O3 composite (35% nanoparticles).

552



the NH proton and an oxygen atom on the Y2O3 sur�face, which weakens the N–H bond and hence it’sstretching intensity [23, 24].

Scanning Electron Microscopy (SEM)

In order to confirm the crystallinity of polyanilinewith Y2O3, the SEM images of samples have beenobtained and are shown in Fig. 4. Micrograph of purePANI exhibit bright granular agglomerates and plate�

let structure of pure Y2O3, whereas the particle size ofPANI–Y2O3 increases and the structure is flakier. Thecomposite PANI–Y2O3 is showing further incrementin particle size and a mixture structure of platelet aswell as flaky structure.

Control Temperature Dependentof PANI–Y2O3 Conductivity

Amount of Y2O3 added. A series of composites withvariable amounts of Y2O3 (10, 25, 35 and 40%) wasprepared by keeping the concentrations of anilinefixed. Increasing the amount of Y2O3 produced com�posites of different conductivity. The conductivities ofthe composites were found to decreases with increas�ing amount of Y2O3 (Fig. 5). The decrease of conduc�tivity with addition of Y2O3 may be attributed toreducing of conductive pathways because of the insu�lated manner of Y2O3, other than the degree of doping.The addition of Y2O3 nanoparticles decreases thedegree of the conjugated π�bonds in polyaniline anddestroys the ordered structure of polymer chains,which results in a decrease in conductivity of the com�posite. Therefore, the presence of Y2O3 Nanoparticlesplays an important role in the conductivity ofPANI/Y2O3 composite.

Temperature dependant DC conductivity. The rela�tion between the DC conductivity and temperature inthe polymer samples can give important information

2 μm(a)

2 μm

2 μm 0.5 μm

@

@

@

(b)

(c) (d)

@

@@

@

@

Fig. 4. SEM of (a), (d) Synthesis of PANI at different magnification. (b) Pure Y2O3, (c) PANI/Y2O3 composites.

Y203

0

25

Conductivity × 105, s/cm

Y2O3 in PANI, %

2

3

1

10PANI 4035

Fig. 5. The conductivities of PANI/Y2O3 composites atdifferent wt % of Y2O3.



concerning the nature of the phenomena related to thecharge transport in a polymer system.

(1)

Here the exponent n in the Eq. (1) [25, 26] is thedimensionality of mechanism, its value can be n = 1, 2or 3 for 1�D, 2�D or 3�D VRH charge transport mech�anism respectively. The effective dimensionality n ofthe charge transport depends on the inter chain cou�pling. Temperature dependent log of conductivity wasfound to have a linear relationship with T–1/4 in case ofpure PANI [27] and PANI–Y2O3 composites. Thisimplies that the charge transport mechanism of thesesamples follows the 3�D variable range hopping (VRH)model. The activation energy is defined as [27, 28]

(2)

The differential of the graph of logσ vs 1/kT givesactivation energy at different temperatures. TheArrhenius exponential law equation is [29].

(3)

By combining Eqs. (2) and (3) we get the followingEq. (4).

(4)

where .

This activation energy can also be exploited to findthe hopping mechanism of charge transport. Con�ducting polymers of different morphologies in thepresence of different dopants at various temperatureregimes generally exhibit conductivity data with expo�

nent of temperature dependence either

equal to 0.25 [29–31] or 0.5 [31–34]. For strong interchain coupling, the exponent γ of temperature depen�dence of DC conductivity is 0.25 and the effectivedimensionality n = 3 and the conductivity data follows

σ σ0 T0/T–( )1/1 n+exp=

Eσ

d σln( )

d 1kT��⎝ ⎠

⎛ ⎞��=

σ σ0 Ea/kT–( )exp=

Ea γKT0T0

T��⎝ ⎠

⎛ ⎞γ 1–

,=

γ 11 n+��=

γ 11 n+��=⎝ ⎠

⎛ ⎞

3D VRH model. For weak inter chain coupling, on theother hand, VRH exponent is 0.5 (n = 1) [34] whichcan be explained in terms of a granular metal model orquasi 1D [35] or the Efros–Shklovskii [36] VRH mod�els. For PANI–Y2O3 by plotting lnEa vs. ln T (Fig. 6)a straight line of slope {–(γ – 1)} equal to 0.70, whichcorresponds to hopping exponent γ ~ 1/4 and n ~ 3.This indicates that the 3�D variable range hopping(VRH) dominates the mechanism of charge transportin the PANI–Y2O3 composite same as 3�D VRHmodel apply in prestine polyaniline [27]. A good fit ofconductivity data to 3D VRH model suggest a stronginter chain coupling in this synthesized PANI–Y2O3.Such a strong interchain interaction coupling causing3D VRH in PANI–Y2O3 [35].

As seen in Table 3 the density of localized statesdecreases while the Average hopping distanceincreases with the addition of Y2O3. The activationenergy obtained from Arrhenius plot, increases withthe increase of temperature. Therefore, logσ is havinglinear relationship with T–1/4 as shown in Fig. 7. From

6.0

−2.0

lnEa, lnev

lnT, lnK

−0.8

−0.2

−1.4

5.8 5.9−2.6

5

3

2

1

4

Fig. 6. lnEa as a function of lnT for (1) PANI, (2)PANI/Y2O3 (10%), (3) PANI/Y2O3 (25%), (4)PANI/Y2O3, (35%) (5) PANI/Y2O3 (40%) composites.

Table 3. Mott parameters of doped PANI with Y2O3 (10, 25, 35 and 40%) composites at 300 K

Sample T0, K Density of states N(Ef), eV–1 cm–3 Hopping length R at 300 K, cm

PANI 10.65 × 107 1.578 × 1019 4.584 × 10–7

PANI + Y2O3 (10%) 40.54 × 107 4.14 × 1018 5.1 × 10–7

PANI + Y2O3 (25%) 13.93 × 108 1.20 × 1018 5.9 × 10–7

PANI + Y2O3 (35%) 16.00 × 108 1.05 × 1018 6.6 × 10–7

PANI + Y2O3 (40%) 88.33 × 107 1.90 × 1018 6.7 × 10–7

554



these results we can say that the strong interchaininteraction exists in PANI as well as in PANI–Y2O3

clay samples but the reason of decrement in D.C. con�ductivity of clay sample is the insulating behavior ofY2O3 and the interruption of Y2O3 layers with interca�lated PANI molecules [36, 37].

CONCLUSIONS

Doped PANI was intercalated into the layers oflamellar structure of Y2O3 by in�situ polymerization.The crystallinity of synthesized samples was studied byXRD diffraction pattern and was found to be improveddue to crystalline nature of Y2O3 in PANI/Y2O3 sam�ple. The enhanced d�spacing of Y2O3 confirmed thatPANI was intercalated into the layers of Y2O3. The lay�ers of Y2O3 interrupted the delocalization of chargecarriers, and weaken the inter�chain interaction due towhich the DC conductivity of PANI is decreased.Temperature dependant DC conductivity showedthree dimensional variable ranges hopping (3D VRH)model. Activation energy, density of states and hop�ping length were calculated and found to be influencedby adding Y2O3.

ACKNOWLEDGMENTS

This work was supported by Higher EducationCommission of Pakistan. HEC project No. PM�IPFP.HRD/HEC/2012/2737.

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0.236

−16

logσ, logS/cm

1/T −1/4, K−1/4

−12

−10

−14

0.228 0.232−18

0.224

1

2

3

4

5

Fig. 7. DC conductivity (σDC) as a function of T–1/4 in alogarithmic scale for (1) PANI (y = –101.6x + 12.95,R2 = 0.983), (2) PANI/Y2O3 (10%) (y = –141.9x + 20.23,

R2 = 0.995), (3) PANI/Y2O3 (25%) (y = –193.2x + 29.81,

R2 = 0.973), (4) PANI/Y2O3 (35%) (y = –200x + 30.58,

R2 = 0.988), (5) PANI/Y2O3 (40%) (y = –172.4x + 23.3,

R2 = 0.985) composites.



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temperature dependent electrical conductivity of polyaniline/y2o3 composites

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