Synthesis, characterization, dielectric andrectification properties of PANI/Nd2O3:Al2O3nanocompositesJuhi Nishat Ansaria, Syed Khasimb,h, Ameena Parveenc,Omar A Al-Hartomyd, Ziad Khattarib,e, Nacer Badib,f and Aashis. S. Royg*

Polyaniline–Nd2O3:Al2O3 nanocomposites were prepared by in situ oxidative polymerization method using differ-ent weight percentages of oxide powders. The prepared nanocomposites were characterized by Fourier trans-form infrared spectroscopy and X-ray diffraction for molecular and crystal structures. Scanning electronmicroscopy and transmission electron microscopy images show the tubular structure of polyaniline nanocompos-ite with embedded metal oxides. The electrical conductivity of the nanocomposites increases with increase intemperature as well as with concentration of Nd2O3:Al2O3 particles in polyaniline. This is because of the hoppingof charge polarons and extended chain length of the nanocomposites as evidenced by the negative thermalcoefficient (NTC) characteristic. A high NTC value of 2.67 was found in nanocomposites with 15wt% of oxideparticles. These nanocomposites show low dielectric constant and dielectric loss; the electrical conductivity ishigher than 0.3 S/cm as confirmed by Cole–Cole plot that indicates a decrease in both grain resistance and bulkresistance of the nanocomposites. The current–voltage and capacitance–voltage measurements were also carriedout. The carrier mobility μ values of pure polyaniline and nanocomposites were found to be 4.27 × 10�3 and1.45 × 10–2 H.M�1, respectively. A significant enhancement in carrier mobility was observed in comparison withthe literature. Copyright © 2016 John Wiley & Sons, Ltd.

Keywords: polymer matrix composites; rectification properties; surface properties; electron microscopy; thermal analysis

INTRODUCTION

For more than a decade, electrically conductive polymer blendsand composite films have gained attention because of their tun-able electrical properties, low weight, low cost, low fabricationtemperatures, good mechanical strength, and environmentalstability. These unique characteristics of conductive organic filmsmake them favorable for many electronics applications,especially in wearable electronics for both consumer anddefense applications.[1,2] Among various conducting polymers,polyaniline (PANI) is a promising candidate for practical applica-tions because of its environmental stability, easy processability,controlled reversibility of electrical properties, and commercialavailability. There are several good reviews on synthesis, physico-chemical, and electrochemical properties of PANI and itsblends.[3–5] Membranes for gas separation with high selectivity,[6]

electromagnetic shielding,[7] biosensors,[8,9] and humiditysensors[10] are among the promising applications of PANIcontaining organic composite films.

A semiconducting oxide such as Nb2O3 can be used as a dop-ant because of its relatively low band gap and tunable electricaland mechanical properties because of the presence of variousvalence states. The presence of defect in mixed oxides helps inhopping and tunnelling of charge carriers through conductingpaths.[11,12] The leakage currents in Nb2O3 were reduced by de-positing thin alternate layers of Al2O3, thereby increasing thenumber of interfaces between distinct oxide layers. The electricalpermittivity of PANI–Nd2O3:Al2O3 composites can be enhancedby increasing the concentration of Nd2O3 without a considerable

* Correspondence to: Aashis. S. Roy, Department of Engineering Chemistry, K.B.NCollege of Engineering, Gulbarga 585 104, Karnataka, India.E-mail: aashisroy@gmail.com

a J. N. AnsariDepartment of Electronics and Communication Engineering, K.C.T EngineeringCollege, Gulbarga 585 104Karnataka, India

b S. Khasim, Z. Khattari, N. BadiDepartment of Physics, University of Tabuk, Tabuk 71491, Kingdom of SaudiArabia

c A. ParveenDepartment of Physics, Government First Grade College, Guirmtkal 585124,India

d O. A. Al-HartomyDepartment of Physics, Faculty of Science, King Abdul Aziz University, 21589,Jeddah, Saudi Arabia

e Z. KhattariDepartment of Physics, Hashemite University, PO Box 150459, Zarqa 13115,Jordan

f N. BadiCenter for Advanced Materials, University of Houston, Houston, TX, 77204-5004, USA

g A. S. RoyDepartment of Engineering Chemistry, K.B.N College of Engineering, Gulbarga585 104Karnataka, India

h S. KhasimDepartment of Physics, PESIT-BSC, Bangalore 560100, India

Research article

Received: 14 October 2015, Revised: 23 November 2015, Accepted: 7 January 2016, Published online in Wiley Online Library: 28 February 2016

(wileyonlinelibrary.com) DOI: 10.1002/pat.3771

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loss in resistivity. The coverage of Nb2O3 monolayer domainsover Al2O3 increased with increasing Nd2O3 loading, and almostfull coverage was obtained at a loading of 15wt%. A sharpincrease in the number of H+ groups, which acted as acid sites,was observed at this loading level. The relationship betweenthe acidic properties and the structure of the material suggestedthat the bridging H+ groups, which were formed at the bound-aries between the domains of the Nd2O3 monolayer, acted asthermally stable acid sites. Therefore, we have made an effortto fabricate electrically conductive PANI–Nd2O3:Al2O3 nanocom-posites. The prepared nanocomposites were characterized byFourier transform infrared spectroscopy (FTIR), X-ray diffraction(XRD), scanning electron microscopy (SEM), and transmissionelectron microscopy (TEM). The electrical parameters of thenanocomposites were studied using the two-probe methods.The diode characteristics were studied for nanocompositescoated on indium tin oxide (ITO) glass by applying a voltagevalues from �3 to 3 V.

EXPERIMENTAL DETAILS

Materials and methods

All used chemicals in our experiments were analytical reagentgrade. The monomer aniline was doubly distilled prior to use.Ammonium persulfate [(NH4)2S2O8] (APS), hydrochloric acid(HCl), neodymium trioxide (Nd2O3), and aluminum trioxide(Al2O3) from Sigma Aldrich—India were used as received. TheITO-coated glass slides were purchased from Blue Star product.The metal contacts were made by using thermal evaporationof aluminum shots purchased from Alfa Aesar with 99.999%purity.

Preparation of polyaniline and its composites

The pristine PANI was prepared by a polymer oxidation methodvia in situ technique as reported in our earlier work.[13] Aniline(0.1M) was dissolved in 1M HCl to form aniline hydrochloride so-lution. Nd2O3 and Al2O3 were added to the aniline hydrochloridesolution with vigorous stirring to keep the Nd2O3:Al2O3

suspended in the solution. A 0.25M of APS, which is an oxidizingagent, was added slowly to the solution with continuous stirringat 0–5°C. After complete addition of APS, the chemical mixturewas kept under stirring process for 8 h. The greenish blackprecipitate of the nanocomposite polymer was recovered byvacuum filtration and washed with acetone. The resultantprecipitate was then dried in an oven for 24 h to achieve a con-stant weight. PANI/Nd2O3:Al2O3 nanocomposites were preparedin weight percent ratio, in which the concentration of Nd2O3

decreases and Al2O3 increases, that is, 5, 10, 15, 20, and 25wt%.

Characterization of PANI nanocomposites

The FTIR spectra of the samples were recorded on a Perkin Elmer1600 spectrophotometer in KBr medium (sample to KBr ratio is1:5) in the wave number range 400 to 4600 cm�1. The surfacemorphology of PANI and its nanocomposites in the form of pel-lets was investigated using Philips XL 30 ESEM on gold substrate.The TEM image of the sample was obtained using JEOL Model1200KVEX instrument operated at 120 kV. The sample for TEManalysis was prepared by dispersing PANI and its nanocompos-ites on carbon-coated copper grids. The sample was kept for5min in vacuum oven under 50°C and then placed on the TEM

grid followed by infrared radiation exposure for 30min in orderto remove residual moister. The DC conductivity was studiedby using 1-mm-thick discs of 10mm in diameter made byapplyinga pressure of 2 T in a UTM-40 universal testing machine(WGS 84 / UTM zone 41N). For temperature-dependent conduc-tivity, the nanocomposite discs were coated with silver pasteon both sides to obtain better contacts. The DC measurementwas carried out by a two-probe method, and the change in resis-tance was measured using a Keithely source meter. The electricalpermittivity and dielectric loss were studied in the frequencyrange from 50Hz to 5MHz by using a Hokki LCR Q meter.

FABRICATION OF THE SCHOTTKY DIODE

Aluminum thin film was deposited at room temperature by ther-mal evaporation under a vacuum chamber of 10�6mbar. A resis-tive tungsten coil was used to evaporate aluminum contacts. TheITO-coated glass substrates were first cleaned by using acetoneand isopropanol solvents, rinsed in distilled water, and finallydried up with a research grade argon gas. The source-substratedistance of 12 cm was maintained for all samples. The evapora-tion rate and the thickness of deposited films were monitoredby quartz crystal monitor.

The Schottky diode was fabricated by using a pure PANI[14]

and 15wt% of PANI/Nd2O3:Al2O3 nanocomposite over ITO-coated glass substrates (Fig. 1). The active material solutionwas obtained by dissolving 15wt% of PANI/Nd2O3:Al2O3 nano-composites in N,N′-dimethylpropylene urea (DMPU) (1.016 gm/cc) solvent and kept under stirring for 3 days and then filteredusing 0.45 μ cringe filter. The filtered PANI/Nd2O3:Al2O3 nano-composite solution was spin coated over cleaned ITO substratesat 3000 rpm for 5min. The coating was annealed for 30minunder vacuum at 100°C at a pressure of 60mm of Hg. The Alelectrodes were vacuum deposited over the nanocompositelayer by using a mechanical mask having openings with activecontact area of 0.04 cm2 each. The aluminum contacts on topof the PANI/Nd2O3:Al2O3 nanocomposite served as the cathode,whereas the bottom ITO-coated glass serves as the anode for thefabricated Schottky diodes. The electrical transport measure-ments were performed on fabricated structures by measuringthe current–voltage (I–V) characteristics between top andbottom electrodes.[15]

RESULTS AND DISCUSSION

Fourier transform infrared spectroscopy

Figure 2a shows the FTIR spectra of pure PANI. The characteristicpeaks around 2922 cm�1 corresponds to C–H stretching of aro-matic ring, 1566 cm�1 is because of the C=C stretching vibrationof quinoid ring, 1493 cm�1 for stretching vibration of benzenoidring, 1406 cm�1 is the characteristic mode of vibration of C–Hbonding of aromatic nuclei, 1302 cm�1 is assigned for thestretching of C–N bonds of aromatic amine, 1142 cm�1 is one ofthe important peaks assigned for measure of degree of delocaliza-tion of electron in aromatic ring, 796 cm�1 corresponds to N–Hrocking vibration mode out of the plain, 592 and 472 cm�1 are be-cause of the bonding of C–H in aromatic ring out of the plain re-spectively.[16] Figure 2b shows the FTIR spectra of 15wt% ofPANI/Nd2O3:Al2O3 nanocomposite. The important characteristicpeaks observed around 1596–1556 cm�1 correspond to the C=Cstretching vibration of quinoid ring, 1487–1484 cm�1 is assigned

Synthesis, Characterization, and Dielectric and Rectification Properties of PANI/Nd2O3:Al2O3 Nanocomposites

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for stretching vibration of benzenoid ring, 1305–1302 cm�1 arebecause of the stretching of C–N bonds of aromatic amine,1145–1140 cm�1 corresponds to the degree of delocalization ofelectron in aromatic ring, 864–738 cm�1 is for N–H of vibration ofrocking mode, 613–584 cm�1 corresponds to vibration of Nd–O–Alin the plain, and 509–497 cm�1 is for the C–H bonding in aromaticring out of the plain respectively.[17]

X-ray’s diffraction studies

Figure 3 shows the typical XRD patterns of (a) Nd2O3:Al2O3 and (b)PANI/Nd2O3:Al2O3 nanocomposites. The orthorhombic structure ofNd2O3:Al2O3 nanooxide (JCPDS 27-1003) (a= 6.168Å, b= 29.312Å,and c=3.936Å) with diffraction 2θ peaks at 30.0°, 31.3°, 42.1°, 47.4°,54.3°, 64.1°, 74.1°, and 77.3° corresponds to (101), (220), (222), (311),(400), (421), (511), and (440) planes as shown in Fig. 3a. There aresimilar peaks observed in the nanocomposite because of the pres-ence of Nd2O3 and Al2O3 fillers as shown in Fig. 3b. In addition tothe nanooxide peaks, a broad absorption peak at 26.40° is becauseof the intermolecular diffraction PANI chain. By comparing the XRD

patterns of metal oxide and its composite, a homogenous distribu-tion of Nd2O3:Al2O3 in PANI matrix is found.

Surface morphology studies by SEM and TEM

Figure 4a shows the SEM image of pure PANI. The PANI fibers arecompact and well connected to each other. These fibers are hor-izontally attached to one another and form a bundle. The averagelength of each fiber is found to be 2μm. Figure 4b shows the SEMimage of 15wt% of PANI/Nd2O3:Al2O3 nanocomposites formed

Figure 1. Schottky diode fabrication using PANI/Nd2O3:Al2O3 Nanocomposites.

Figure 2 (a,b). FTIR spectra of pure metal oxide and its nanocomposites.

Figure 3 (a,b). XRD pattern of pure PANI and its nanocomposites.

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using HCl as a protonic acid. It is found that the nanocompositesare formed with tube-like structure, uniform in length, and highlydispersed. The TEM images of the Nd2O3:Al2O3 nanoparticlesshow the orthorhombic shaped structure in Fig. 4c. The surfaceto volume ratio of Nd2O3:Al2O3 nanoparticles increases while go-ing from bulk to nanograin. The particle size is found to be 7 nm.The spherical morphology of Nd2O3:Al2O3 nanoparticles help intransport mechanism as a result of the high surface area.

ELECTRICAL PROPERTY MEASUREMENTS

The fabricated PANI/Nd2O3:Al2O3 nanocomposites were investi-gated for DC conductivity measurements. Figure 5 shows the plotof σdc as a function of temperature for PANI and PANI/Nd2O3:Al2O3

nanocomposites in the temperature range from 40 to 200°C. The

DC conductivity remains almost constant up to 80°C, and then, itincreases steadily up to 200°C, which reflects the characteristicbehavior of semiconducting materials. At higher temperatures,the conductivity increases because of the hopping of polaronsfrom one localized site to another. The temperature dependenceof conductivity of the composites exhibits a typical semiconductorbehavior, and it can be expressed by the one-dimensional variablerange hopping model proposed by Mott[18–20] as follows,

σ Tð Þ ¼ σ0 exp�- T0=Tð Þ1=2� (1)

T0 ¼ 8α=ZN EFð Þ KB (2)

where α�1 is the localization length, N(EF) is the density ofstates at Fermi level, KB is the Boltzmann constant, and Z is thenumber of nearest neighbor chains.

Among all the composites the 15wt% of Nd2O3:Al2O3-dopedPANI nanocomposites show high conductivity of 0.1 S/cm. Thismay be because of the decrease in distance between theentangled polymer chains and Nd2O3 and Al2O3 nanoparticles,which combined with high activation energy of 2.91 eV, makeseasy the hopping of the polarons from one site to another.Figure 6 shows the variation of the negative thermal coefficient(NTC) α with respect to weight percentages of Nd2O3:Al2O3 inPANI matrix. It is clearly found that α value increases withincrease in Nd2O3:Al2O3 concentration. At 15wt%, the thermalresistance of the matrix enhances because of the strong bondingbetween Nd2O3:Al2O3 nanoparticles and matrix.[21] The negativecoefficient values indicate that these materials act as semicon-ductor at higher temperature.[22] When the temperature risesup, the average amplitude of the atoms’ vibration within thematrix increases. This, in turn, increases the separation betweenthe Nd2O3:Al2O3 atoms causing the PANI polymer to expandand the conduction path network in nanocomposites toincrease. It is believed that the material does not undergo anyphase change and the expansion can easily be related to the

Figure 4. SEM and TEM image of (a) PANI and (b) PANI/Nd2O3:Al2O3 nanocomposites.

Figure 5. DC conductivity against temperature.

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temperature change. The thermal expansion will cause signifi-cant stress in the nanocomposite matrix and does not allow forexpansion and contraction of polymer nanocomposites thatincrease electron density in the junction and cause resultsblocking of charge carriers. The expansion of the nanocompositematrix increases the conduction path, resulting the highconductivity of the nanocomposites.

DIELECTRIC STUDY

The variation of the real part of the electrical permittivity (ε′) as afunction of frequency for pure PANI and for various weight per-centages of Nd2O3:Al2O3 in PANI nanocomposites is shown inFig. 7. It is observed that, in all these composites, the dielectricconstant is high at low frequencies, and also, the value is highfor higher weight percentage of Nd2O3:Al2O3 in polymer matrixand sharply decreases with increase in applied frequency and al-most becomes constant for frequencies greater than 103 Hz for allcases. High values of electrical permittivity at lower frequencyrange are because of maximum accumulated charge carriers atthe interface of grain boundaries. The strong frequency disper-sion of the electrical permittivity is observed in the low-frequencyregion.[23,24] The observed behavior may be because of the dipole

polarization along with Maxwell–Wagner–Sillars (MWS) polariza-tion[25] at the interface of electrode and nanocomposite surfacetaking place in these materials that leads to a large dispersionthroughout the frequency range. The interaction between PANIchains and surface of Nd2O3:Al2O3 nanoparticles restricts the mo-tion of dipoles that leads to decrease of ɛ′ at higher frequencies.Among all composites, it is observed that 15wt% of PANI–Nd2O3:Al2O3 nanocomposite shows low relative electrical permit-tivity value of 689 F/m compared with other composites.Figure 8 shows the variation of imaginary part of the electrical

permittivity (ε″) with frequency for different weight percentagesof Nd2O3:Al2O3 in PANI at room temperature. The imaginary partof the electrical permittivity has also a similar trend as that of itsreal part with respect to frequency change and becomes almostconstant beyond 103 Hz, but the magnitude of the imaginarypart is higher than that of relative permittivity (ε′). At room tem-perature, the value of ε″ is high for higher weight percentage offillers in matrix and decreases with increase in applied frequencyfor all the composites. The decrease in the imaginary permittivityvalue is because of dipole polarization, that is, the rotation of di-poles between two equivalent equilibrium positions and MWS

Figure 6. NTC plot of PANI/Nd2O3:Al2O3 nanocomposites.

Figure 7. Variation of relative permittivity as a function of appliedfrequency.

Figure 8. Variation of imaginary permittivity as a function of appliedfrequency.

Figure 9. Variation of quality factor for different composition.

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polarization that causes large scattering of charge carrier’s re-sults high dispersion throughout the frequency range.[26–28]

The variation of quality factor (Q) as a function of frequency isshown in Fig. 9 for various weight percentages of PANI–Nd2O3:Al2O3 nanocomposites. It is observed that the Q values changewith applied frequencies and increases with increasing the fillerconcentration, forming a bell shape. The quality factor valuereaches its maximum at a frequency around 104 Hz after whichit gradually decreases because of over damping, reflecting thefact that the charge carriers do not oscillate at all. Among allnanocomposites, 15wt% shows high-quality factor because ofthe formation of R, L, and C circuit within the framework ofpolymer network. The lower the parallel resistance, the moreeffect it will have in damping the circuit and thus the lower the Q.At equilibrium, a hump is formed because of the steady state ofelectron flow through the polymer composites asymptotically.[29–31]

Figure 10 shows the variation of tanδ (loss) as a function of fre-quency for various weight percentages of Nd2O3:Al2O3 in PANI.At lower frequencies, the dielectric loss is constant as a result of re-laxation process, and it decreases at higher frequencies above5.103Hz. The 15wt% nanocomposites show low dielectric lossranging from 2.3 and down to 0.1 at frequencies above

106Hz.[32] Therefore, thesematerials can be used as low k-dielectricmaterial in electronic transistors, microelectronic devices, etc.

The Cole–Cole graphs indicate a decrease in electrical resistancewith increasing filler concentration as well as with the applied fre-quency, as shown in Fig. 11. The impedance value depends on thebulk resistance and grain resistance in a complex LCR circuit. Thebulk resistance and grain resistance decrease with increase inNd2O3:Al2O3 concentration that makes the impedance value alsoto decrease. As the filler concentration increases, area under thecurve decreases up to the percolation threshold, indicating a sharpdrop in the resistance. The formation of a semicircular arc indicatesthat the presence of two different components in the compositesforms a series resistor and a geometrical capacitance, as shownin inset figure. A decrease in the arc area indicates increase in thebulk conductivity. The formation of two semicircles is observedand it shows that the relaxation time decreases with increase in ap-plied frequency until 15wt% and increases thereafter, whichmightbe because of increase in grain resistance. The variation of relaxa-tion time against different weight percentage of Nd2O3:Al2O3 inPANI nanocomposites are calculated from Cole–Cole plots byusing the formula.[33]

τ ¼ 0:5 πfc (3)

where fc is the maximum peak position of Cole–Cole plot in aparticular frequency range. The analysis of Cole–Cole plots sug-gests that there is an increase in relaxation time distribution forhigher percentage of Nd2O3:Al2O3 nanoparticles in polymermatrix. The 15wt% of PANI/Nd2O3:Al2O3 shows the lowestrelaxation time of 0.31μs indicating a much faster flow of chargecarriers, which may be because of low bulk resistance and lessgrain boundaries. The formation of low grain boundariessupports easy hopping and tunnelling of polorons andbipolorons from one island to another.

Figure 12 shows the plot of σac as a function of frequency forpure PANI and PANI/Nd2O3:Al2O3 nanocomposites of variousweight percentages in the frequency range from 102 to 106 Hz.The AC conductivity remains constant up to 105 Hz, and thereaf-ter, it increases steeply, which is a characteristic feature of disor-dered materials. At higher frequencies, σac increases because ofcontribution of polarons, which are moving along smaller andsmaller distances in a polymer chain. The increase of σac athigher frequencies is because of the charge motion in the amor-phous region, and this supports the presence of isolatedFigure 10. Variation of tan delta as a function of applied frequency.

Figure 11. Cole–Cole plot for PANI/Nd2O3:Al2O3 nanocomposites. Figure 12. Variation of σac as a function of applied frequency.

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polarons in this region. The 15wt% of PANI/Nd2O3:Al2O3 showshigh conductivity of 0.3 S cm�1 as a result of low dielectricconstant because of the polarization of charges.

Current density–voltage characteristics

The variation of J–V characteristics shown in Fig. 13 was measuredby varying the voltage from�3 to +3V with 0.1 V increment usingKeithley 2420 C source meters recorded with Lab tracer software.The linear J–V dependence of ITO/nanocomposites/Al indicates asymmetric and non-ohmic behavior of this device in the testedvoltage range. Therefore, the electrical connections of the deviceare polarity independent. This result illustrates that both ITO andaluminum having work function ≈4.2 eV form Schottky contactwith PANI/Nd2O3:Al2O3 nanocomposites that have a work functionvalue close to that of PANI, that is, ≈5.3 eV. The specific contact re-sistance was derived from reciprocal of the derivative of the cur-rent density with respect to the voltage across the interface. TheJ–V characteristics were analyzed using the following equation

R ¼ dJdV

� ��1

(4)

The J–V plot implies that aluminum contact formed over anactive layer is a Schottky type. The current density J forPANI/Nd2O3:Al2O3 nanocomposites lies above the one for PANI.This increase in current density is probably because of the inter-face effect that gives a more effective area of the metal contactin PANI/Nd2O3:Al2O3 nanocomposites. Moreover, aluminum con-tact with the PANI/Nd2O3:Al2O3 nanocomposite film is mechani-cally better because Nd2O3:Al2O3 improved packing at theinterface of PANI and metal electrode.[34] The improved interfa-cial contact between metal and conducting polymer enhances

the charge injection at the interface causing current flow to in-crease. The Schottky diode junction parameters such as idealityfactor (n), barrier height (Φ), charge mobility (μ), and currentdensity (J) for the fabricated diodes are shown in Table 1.

Capacitance–voltage characteristics

The capacitance–voltage (C–V) characteristics of ITO/nanocom-posites/Al electrode were measured as shown in Fig. 14. Themetal/semiconductor junction has a specific capacitancebecause of a space charge in the depletion layer, which dependson junction voltage. The plots of 1/C1/2 versus bias voltage arelinear that indicates the formation of Schottky junction. There-fore, it follows a standard Mott–Schottky relationship:

1

C2 ¼2 Vbi � V � kT

q

� �qε0εSA2Nd

πr2 (5)

where C is the diode capacitance, Vbi is the built-in voltage, εS isthe polymer relative dielectric constant, ε0 is the electrical permit-tivity in vacuum, V is the applied voltage, q is the charge, A is thediode active area, kT/q is the thermal voltage at 303K, and Nd isthe charge carrier concentration. The charge carrier concentrationcan be determined from the slope of 1/C2 versus V plots. From theextrapolated intercept on voltage axis, Vbi can be estimated. C–Vplots for PANI and PANI/Nd2O3:Al2O3 nanocomposite-baseddevices show that the capacitance is strongly dependent ondopants as well as on the bias voltage. The capacitance decreaseswith decrease in the applied voltage. These results show that thebarrier height decreases as the dopant increases up to 15wt% inthe PANI and the number of charge carrier concentration increasessimultaneously.[35]

The carrier mobility μ was determined from the relation ofconductivity (σ =Νdεμ) provided that all ionized charge carrierstake part in the conductivity. The carrier mobility μ values ofPANI and PANI/Nd2O3:Al2O3 nanocomposites are found to be4.27 × 10�3 and 1.45 × 10�2, respectively, and this is a significantincrement compare to reported data.[36,37] The number of chargecarrier concentrations and the mobility of these carriers increasewith the increase of both Nd2O3:Al2O3 concentration and theapplied voltage. These results suggest that tunneling or hoppingmechanism in these devices may be equally important as inthose involving thermionic emission process.[38]

Table 1. Schottky diode junction parameters ideality factor(n), barrier height (Φ), charge mobility (μ), and current density(J) for the fabricated diodes

Junction parametersSchottkydiodes

Js(A cm�2)

ΦC-V

(eV)n Nd

(cm�3)μ

PANI 4.72× 10�5

0.869 3.21 3.98× 1017

4.27× 10�3

ITO/nanocomposites/Al

3.45× 10�4

0.689 2.93 5.17× 1017

1.45× 10�2

Figure 13. J–V plots of PANI and its 15 wt% of nanocomposites.

Figure 14. C–V plots of PANI and its 15 wt% of nanocomposites.

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CONCLUSIONS

Polyaniline–Nd2O3:Al2O3 nanocomposites were prepared by insitu oxidative polymerization method using different weight per-centages of oxide powders. The prepared nanocomposites werecharacterized by FTIR and XRD for molecular and crystal struc-tures. The FTIR shows that important characteristic peaks at1566 cm�1 are because of the C=C stretching vibration of quin-oid ring, 1493 cm�1 is for stretching vibration of benzenoid ring,and 509 cm�1 at M–O peaks confirms the formation of nanocom-posites. XRD spectra showed the orthorhombic structure ofNd2O3:Al2O3 nanooxide that is retained after formation of nano-composites. SEM and TEM images show the tubular structure ofPANI nanocomposite with embedded metal oxides. The electri-cal conductivity of the nanocomposites increases with increasein temperature as well as with concentration of Nd2O3:Al2O3

nanoparticles in PANI. This is because of the hopping of polaronsand extended chain length of the nanocomposites as evidencedby the NTC characteristic. A high NTC value of 2.67 was found innanocomposites with 15wt%. These nanocomposites have lowdielectric constant and dielectric loss values; the high electricalconductivity is above 0.3 S/cm. Cole–Cole plot indicates thatboth grain resistance and bulk resistance decrease with decreasein area under the curve of the nanocomposites. The carriermobility (μ) values of pure PANI and nanocomposites are4.27 × 10–3 and 1.45 × 10–2 H.M�1 respectively. A significant en-hancement in carrier mobility was observed in comparison withthe literature. This study may provide a better route for futuretechnological applications of embedded conductive polymers.

Acknowledgments

The authors would like to acknowledge financial support for thiswork, from the Deanship of Scientific research (DSR), Universityof Tabuk, Tabuk, Saudi Arabia, under grant no. S-0146/1436.

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Synthesis, Characterization, and Dielectric and Rectification Properties of PANI/Nd2O3:Al2O3 Nanocomposites

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