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Journal of Molecular Structure 1100 (2015) 546e554

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Journal of Molecular Structure

journal homepage: http : / /www.elsevier .com/locate/molstruc

Optical, magnetic and electrical properties of multifunctional Cr3þ:Polyethylene oxide (PEO) þ polyvinylpyrrolidone (PVP) polymercomposites

K. Naveen Kumar*, J.L. Rao, Y.C. RatnakaramDepartment of Physics, Sri Venkateswara University, Tirupati 517502, India

a r t i c l e i n f o

Article history:Received 1 April 2015Received in revised form1 June 2015Accepted 29 July 2015Available online 30 July 2015

Keywords:Cr3þ:PEO þ PVP polymer filmsOpticalMagneticElectrical propertiesMultifunctional applications

* Corresponding author.E-mail address: knaveenphy@gmail.com (K. Navee

http://dx.doi.org/10.1016/j.molstruc.2015.07.0660022-2860/© 2015 Published by Elsevier B.V.

a b s t r a c t

Multifunctional polymer composite films of PEO þ PVP and also doped with Cr3þ ions in differentconcentrations have been synthesized by a solution casting method. The semi-crystalline nature of thepolymer films was confirmed by XRD studies. Raman spectral analysis confirms the complex formation ofthe polymer with dopant ions. The optical absorption spectrum of Cr3þ doped polymer exhibits threeabsorption bands pertaining to Cr3þ ions in octahedral symmetry. From the absorption spectrum, Racahparameters were evaluated. The red emission at 614 nm (4T2g/4A2g) has been observed for the Cr3þ:PEO þ PVP polymer under the UV excitation. EPR spectra of Cr3þ ions doped polymers at differentconcentrations of Cr3þ ions exhibit resonance signals which are characteristic of Cr3þ ions in the octa-hedral symmetry. Cr3þ: PEO þ PVP revealed the superparamagnetic nature based on the trends onVibrational Sample Magnetometer profiles. Cr3þ(0.1 wt%): PEO þ PVP polymer reveals high ionic con-ductivity in the order of 1.14 � 10�5 S/cm at 373 K. Dielectric constant behaviour has also been analysedwith respect to frequency.

© 2015 Published by Elsevier B.V.

1. Introduction

Polymers have traditionally been considered as excellent hostmatrices of composite materials. Several advanced polymercomposites have been synthesized with a broad assortment ofinclusions, such as metals and semiconductors [1]. Manyattractive properties of polymers such as flexibility, compact-ness, light weight, non-corrosiveness, mechanical strength,availability in different geometries, durability and dielectrictunability that are utilized along with novel magnetic and opticalproperties of embedded with transition metal ions to makemultifunctional materials [2,3]. Magnetism in non-metallic,molecular materials are a welcome phenomenon from a tech-nological perspective since these materials are usually lessexpensive to produce than their metallic counterparts. The in-clusion of ferromagnetic or superparamagnetic ions in polymersis especially important in various potential applications, such asspin-polarized devices, magnetic recording media and high

n Kumar).

frequency applications [4].Conducting polymers have also been found in various appli-

cations due to their flexibility and ease of processing combinedwith their high conductivity. Some of the potential applicationsinclude electromagnetic shielding in the form of coatings orsheaths [5]. Composite materials possessing both conducting andmagnetic properties are extremely useful due to their potentialapplications in electrochemical display devices, sensors, solidpolymer electrolytes and broadband microwave absorbers [6].Polymer electrolytes have become the subject of significant in-terest because of their potential applications in batteries andother electrochemical devices. The ionic conductivity of a poly-mer is extremely dependent on the compactness of the addedsalts. A better understanding of the dynamics and segmentalrelaxation of polymer films can be gained by means of conduc-tivity relaxation spectral study. Magnetic ions embedded inpolymer matrices possess both electrical and magnetic proper-ties simultaneously. These materials have been identified asexcellent potential materials for electromagnetic device appli-cations [7], e.g. electromagnetic interference suppression. High-spin organic polyradical molecules with chemical stability will

Fig. 1. The XRD profiles of PEO þ PVP, Cr3þ (0.025, 0.05, 0.075 & 0.1 wt%) dopedPEO þ PVP blended polymer films.

K. Naveen Kumar et al. / Journal of Molecular Structure 1100 (2015) 546e554 547

open a new field of magnetic organic materials for sensor ap-plications [8].

A polymer that exhibits one or more properties as a result ofdifferent operations has been considered as multifunctionalpolymer. By changing the functional group of a polymer or by theaddition of nano materials, the polymer composite propertiescould be remarkably changed. Multi functional polymer nanocomposites have been studied by using certain nano particles toobtain several properties in a single polymer composite [9].However, as of now, no reports are available that are based ontransition metal ions doped polymer composites which exhibitmultifunctional properties such as electrical, magnetic and opticalproperties.

Polyethylene oxide (PEO) is an interesting base materialbecause of its high thermal stability. PEO is a semi-crystallinepolymer, that displays both amorphous and crystalline phases atroom temperature [10]. Polyvinylpyrrolidone (PVP) was selectedas the second polymer component for the preparation of polymerblend with PEO. PVP is an amorphous polymer, which can permitfaster ionic mobility when compared to other semi-crystallinepolymers. Due to the presence of carbonyl group(C]O) in theside chains of PVP, it forms a variety of complexes with differentinorganic salts. Another advantage of using PVP is that it can bethermally cross-linked, resulting in a good thermal stability andmechanical strength of the blended material and also because ofthe solubility of PVP in water [11,12]. In the present study, theauthors made an attempt to study different properties of thesecomposite films made by blending with PEO, PVP and using Cr3þ

ions as a paramagnetic impurity ions for multifunctionalapplications.

2. Experimental studies

Blended polymer films were prepared by using a traditionalsolution casting method with triple distilled water. Polyethyleneoxide (PEO) (MW ¼ 6 � 105) and polyvinylpyrolidone (PVP)(MW ¼ 13 � 105) were obtained from SigmaeAldrich. Films of(thickness ~100 mm) PEO þ PVP blended polymers were dopedwith chromium chloride. The precursor polymer materials (PEO:PVP) were measured in (50 wt%:50 wt%) and the salts were takenin different weight percentages (0.1, 0.075, 0.05 and 0.025 wt %).Triple distilled water was used as solvent. PEO, PVP and dopantsalts were dissolved in triple distilled water and stirred for10e12 h to get a homogeneous mixture at room temperature. Thesolution was cast onto polypropylene dishes and allowed toevaporate slowly at room temperature. The dried compositepolymer films were peeled off from the polypropylene dishes andanalysed.

The XRD spectra of Cr3þ: PEO þ PVP polymer blended filmswere measured on SEIFERT 303 TT X-ray diffractometer with CuKa

(line of 1.5405 Å), and it was operated at 40 KV voltage and 50 mAanode current. Scanning electron microscopy (SEM-CARL ZEISSEVO MA 15) and Energy Dispersive X-ray spectrometry (EDAX)analysis attached to the SEM were used to investigate themorphology and elemental analysis of the sample was carriedout. Raman spectra of Cr3þ: PEO þ PVP films were obtained atroom temperature in the range of 800e1800 cm�1 usingLabRam HR 800 confocal Raman Spectrometer with Nd: YAGlaser source (532 nm). VSM measurement was made on aLakeshore new 7400 series at room temperature. The electronparamagnetic resonance spectral measurements were carriedout by using a Bruker EMX EPR Spectrometer. The impedancemeasurements were performed using a computer controlledphase sensitive multimeter (PSM 1700) in the frequency rangeof 1 Hz-1 MHz at different temperatures.

3. Results and discussion

3.1. XRD analysis

The measured XRD profiles of the films are shown in Fig. 1.PEO þ PVP polymer blended films exhibit crystalline peaks of PEO,having one peak with a maximum intensity at 19.2� from the crystalplane (12 0), another intense peak at 23.6� from the crystal plane (112) and relatively less intense peak at 27.1� that broad peak indicatesthe amorphous nature. No such well defined sharp peaks areobserved for PVP, instead a broad peak is observed at 13�, whichsuggests the amorphous nature of PVP. The characteristic peaks ofpure PEOþ PVP complex showavariation in intensity suggesting thatthe ordering of the PEO polymer crystallinity is disturbed due to thecoordination interactions between the chromium ions and ethericoxygens. These observations confirm that the present polymer blendsystems possess both crystalline and amorphous segments. However,with the addition of small amount of chromium ion to the blendedfilms, these could show semi-crystalline nature [13,14].

3.2. Scanning electron microscopy & EDAX analysis

Fig. 2 (a) & (b) shows the SEM images of the pure and Cr3þ ionsdoped PEO þ PVP blended polymer films. All the figures show therough surface morphology having the semi-crystalline nature. In allconcentrations of the dopants within the blended polymer, they areexhibit this semi-crystallinenaturewhichare ingoodagreementwiththe XRD results [15]. On addition of Cr3þ ions to the blended polymerfilm, the roughness decreases, which indicates the fact that thesemicrystalline nature decreases. The ionic conductivity increaseswith the addition of Cr3þ ions. Thismay be due to the decrease in thesemicrystalline nature of the blended polymer film. This is wellexplained in impedanceanalysis. Inorder toverify theelements in thematerial, an EDAX profile was done alongside SEM image, and thepresence of C, O and Cr ions in the samples are confirmed.

3.3. Raman spectral analysis

Fig. 3(a) shows the Raman spectra of pure and Cr3þ ions dopedPEO þ PVP polymer films for different concentrations. The bands

Fig. 2. SEM image with EDAX profile of (a) PEO þ PVP (b) Cr3þ (0.1 wt%) doped blended polymer film.

K. Naveen Kumar et al. / Journal of Molecular Structure 1100 (2015) 546e554548

observed at 1235 cm�1, 1426 cm�1 and 1666 cm�1 are attributed tothe CeN stretching, CeH bending and C]O vibrations of PVPrespectively [16]. The bands observed at 1067 cm�1, 1040 cm�1,932 cm�1, 862 cm�1, 846 cm�1, and 1395 cm�1 are ascribed to PEOin the polymer complex [17]. Two bands observed at 862 cm�1 and846 cm�1 are attributed to the individual active modes of CH2rocking and CO stretching modes of PEO respectively. The signifi-cant spectral band at 932 cm�1is assigned to CO stretching mixedwith the CH2 rocking vibrations of PEO. Moreover, the bandsobserved at 1340 cm�1 and 1367 cm�1 are in good agreement withthe earlier reports [18]. In addition to these bands, new bands arenoticed at 1445 cm�1 and 1464 cm�1 which are attributed to thepresence of PEO.

On adding transition metal ions with increasing concentrationto the PEO þ PVP, a slight shift in band position at 1063 cm�1 to-wards a higher wavenumber side is observed when compared tohost polymer matrix due to the CeO stretching and/or rockingmodes of CH2 vibrations and this band became assymetric with the

addition of transition metal ions. This attests to the complex for-mation between the transition metal ion and the host PEO þ PVPpolymer [19]. It has been observed that the Raman band positionscorresponding to CeC stretching vibrations at 846 and 862 cm�1 inthe pure blended polymer were observed to have broadened andshifted to higher wavenumber side with increasing the Cr3þ ionconcentration. These peaks are identified as asymmetric naturewith increasing the Cr3þ ion concentration as shown in Fig. 3(b).This indicates the formation of ion pairs. The significant changes inthe CeC vibrational band can be associated with the formation ofionic bond with less polarization. The intensity of the band at1666 cm�1 attributed to PVP is also found to have broadened andshifted to higher wavenumber side with increasing dopant con-centration. This broadness and shifting might be due to the stronginteraction taking place between the dissociated paramagnetic ionsand the blended polymer. The semi-crystalline nature found withincreasing the Cr3þ concentration has been confirmed by thebroadening of the Raman modes at 1445 cm�1 and 1365 cm�1

Fig. 3. Raman Spectra of PEO þ PVP, Cr3þ (0.025, 0.05, 0.075 & 0.1 wt%): PEO þ PVP blended polymer films in the range of (a) 800e1800 cm�1(b) 830e880 cm�1 & (c)920e960 cm�1.

K. Naveen Kumar et al. / Journal of Molecular Structure 1100 (2015) 546e554 549

which is attributed to the combination of CeH bending and OeHbending vibrations. This is in good agreement with the XRD results.In Fig. 3(c), the spectra of the blended polymer film exhibit themostintense band around at 936 cm�1, which is associated with thesymmetric stretching mode of the anion. This mode is veryimportant and well suited for investigating ionic association [16].The broadening of the Raman band at 936 cm�1 increases, withincreasing salt concentration. When the salt concentration isincreased, the main band shifts to the higher wavenumber side andbecomes asymmetric, as shown in Fig. 3(c). This is also one of theevidences for the formation of ion pairs. In the case of PEO þ PVP:Cr3þ, only a single band at 1034 cm�1 is seen, which is associatedwith the presence of the free chloride anion The broadening inRaman spectra is usually an indication of amorphous or semi-crystalline nature of the blended polymer [20]. The semi crystal-line nature of the polymer blend has also been confirmed by XRDanalysis.

3.4. Optical absorption studies

The optical absorption spectra of pure and Cr3þ: PEO þ PVPblended polymer films are shown in Fig. 4. No absorption bands areobserved for the pure sample. Cr3þ doped polymers show twobroad absorption bands at 432 nm and 600 nm and aweak hump at689 nm. The two broad bands at 432 nm (23184 cm�1) and 600 nm(16666 cm�1) are assigned to the transition 4A2g (F) / 4T1g (F) and4A2g (F) / 4T2g (F) respectively. A weak hump observed at 689 nm(14513 cm�1) is assigned to 4A2g (F) / 2Eg (G) transition.

The crystal field parameter Dq is evaluated from the band po-sition of 4A2g /

4T2g as

Dq ¼ E�4A2g/

4T2g�

10(1)

The value of Racah interelectronic repulsion parameter is

Fig. 4. Optical absorption spectra of pure & Cr3þ(0.1): PEO þ PVP blended polymerfilm.

Fig. 5. (a) Excitation & (b) Emission spectra of Cr3þ (0.025, 0.05, 0.075 & 0.1 wt%)doped PEO þ PVP blended polymer film.

K. Naveen Kumar et al. / Journal of Molecular Structure 1100 (2015) 546e554550

evaluated using the relations given by

DqB

¼ 15ðX � 8ÞX2 � 10X

(2)

where X ¼ (E1 � E2)/Dq.Here E1 and E2 represent the energies of 4A2g/

4T1g and4A2g/

4T2g transitions respectively. The crystal field parameter Dqevaluated is found to be 1666 cm�1. This value is in the expectedorder for Cr3þ ions in octahedral symmetry [21]. The parameter B isfound to be B ¼ 646 cm�1. The value [22] of the inter electronicrepulsion parameter B for the Cr3þ free ion is 918 cm�1. A com-parison with the observed B value with the free ion value indicatesthat the B value decreased by 30%, which indicates a moderatecovalant bonding effects. In aweak crystal field site, the value of Dq/B < 2.3 and in a strong crystal field site Dq/B > 2.3. For an inter-mediate crystal field [23] Dq/B ¼ 2.3. In the present work, the ratioof Dq/B is found to be 2.58, which suggests that the Cr3þ ions aresituated in strong crystal field. The energy matrices for the d3

configuration were diagonalized for values of Dq, B and C and agood fit is obtained for Dq ¼ 1666 cm�1; B ¼ 646 cm�1; andC ¼ 2906 cm�1.

3.5. Photoluminescence analysis

Fig. 5(a) shows the excitation spectrum of the Cr3þ dopedPEO þ PVP blended polymer film, which shows three sharp exci-tation bands located at 310 nm, 343 nm and 373 nm. Fig 5(b) showsthe emission spectrum of Cr3þ doped PEO þ PVP polymer film. Theemission spectrum is recorded at 343 nm excitationwavelength. Anintense band is observed at 614 nm and two relatively less intensepeaks are observed at 562 nm and 653 nm. These emission bandsare assigned to the electronic transitions of 4T1g / 4A2g at 562 nm,4T2g / 4A2g at 614 nm and 2T1g / 4A2g at 653 nm [24,25].

3.6. Electron paramagnetic resonance spectral studies

The EPR spectra for pure and Cr3þ doped polymers are shown inFig. 6 (a) and 6(b) respectively. For the undoped polymer film anintense resonance signal is observed at 3002 G and the effective gvalue is calculated and found to be g ¼ 1.92. This intense resonance

signal is due to etheric oxygen radical ions [26]. The EPR spectra ofCr3þ doped polymer samples exhibit two resonance signals. Aweakand low field resonance signal is observed at 1380 G and theeffective g value is found to be g ¼ 4.59. This is due to the isolatedCr3þ ions. The intense resonance signal at the higher magnetic fieldend with the effective g value at 1.99 is assigned to exchangecoupled Cr3þ ions and isolated Cr3þ ions [27]. The number of spins(Ns) participating in the resonance is calculated for g ¼ 1.99 reso-nance signal by using the formula; Ns ¼ 0.285 I(DH)2 where I is thepeak to peak height and DH is the line width (in G), and it is foundto be 0.3 � 1010 [28].

3.7. VSM analysis

Fig. 7(a) shows the hysteresis curves of the magnetization (M) asa function of magnetic field (H) obtained at room temperature for apure PEO þ PVP blended polymer sample. The film exhibits itsparamagnetic nature, which can be attributed to the existence offree mobile spins in the blended polymer films as seen in the EPRspectrum for the undoped polymer. However a close examinationat lower fields [inset of Fig. 7 (a)] indicates the presence of weakferromagnetic feature in the sample. This is the result of a situationwhereby weak ferromagnetic signal was superimposed on the su-per paramagnetic signal. The saturation magnetization and rema-nent magnetic fields are estimated to be 4.416�10�4 and1.524 � 10�5 emu [29].

Following the literature [30], measured hysteresis loop iscontributed by the ferromagnetism and paramagnetic characters of

Fig. 6. EPR spectra of (a) PEO þ PVP & (b) Cr3þ (0.025, 0.05, 0.075 & 0.1 wt%) dopedPEO þ PVP blended polymer films.

K. Naveen Kumar et al. / Journal of Molecular Structure 1100 (2015) 546e554 551

the sample, which can be separated, using the expression:

MðHÞ ¼ 2Msp

tan�1�H±HcHc

tan�pS2

��þ cH (3)

whereMs and Hc are the saturation magnetization and coercivity ofthe ferromagnetic component, respectively. S is defined as the ratioof remanent magnetization (Mr) to saturation magnetization (Ms)of the ferromagnetic component and c is the magnetic suscepti-bility of the paramagnetic component.

Cr3þ: PEO þ PVP samples exhibit superparamagnetic characterwith a weak ferromagnetic signal. The lower field ferromagneticnature increases with an increase in Cr3þ ions concentration atroom temperature as shown in Fig. 7 (b). The saturation magneti-zation increases with increasing the Cr3þ ions concentration, whichmay be due to the enhancement of mobile spins in the PEO þ PVPpolymer films. Coercive field (Hc), Saturation Magnetization (Ms)and Remanant Magnetic field (Mr) values for pure and differentconcentrations of Cr3þ doped PEO þ PVP polymer films are tabu-lated in Table 1. A maximum ferromagnetic signal is observed at0.1wt% concentration of the Cr3þ ions in the blended polymer film,when compared to other concentrations at lower fields. Some re-ports [31] stated that the appearance of ferromagnetism in transi-tion metal (TM) doped samples could be due to the exchangeinteractions between the TM ions and the O ions spin moment.Likewise, the origin of magnetic properties of Cr3þ doped films

could be induced by Cr 3d and O 2p spin moments [32]. From Fig. 7(b), it is clear that the strong super paramagnetic signal is super-imposed on the weak ferromagnetic signal. The Cr3þ dopedPEO þ PVP blended polymers exhibit the strong super para-magnetic character with a weak ferromagnetic nature.

3.8. Impedance spectroscopy analysis

The samples were vacuum dried at 300 K for 1 h and the mea-surements were done by sandwiching the polymer film betweentwo aluminium electrodes. Impedance spectroscopy has become animportant method for the investigation of ionic conductivity ofblended polymer films. The impedance, dielectric loss and dielec-tric constant parameters were clearly reported in previous work[33]. Fig. 8 shows the complex impedance plane plots (Z0 vs Z

00) of

PEO þ PVP blended film doped with Cr3þ containing salts withincreasing the temperature. Among all the concentrations of Cr3þ

ions in the blended polymer film, the 0.1 wt% concentration ex-hibits a prominent ionic conductivity at room temperature. For thisconcentration (0.1 wt% of Cr3þ) only, the ionic conductivity studywas carried out with respect to temperature, upto 373 K. From thefigure, two well defined regions: such as a high frequency semi-circle related to the parallel combination of a resistor and capacitorare obvious. Low frequency spike representing the formation ofdouble layer capacitance at the electrode electrolyte interface, dueto the migration of ions at low frequency. The low frequencyresponse appearing as an inclined spike at an angle less than 900 tothe real axis indicates the inhomogeneous nature of the electrode-electrolyte interface. By the intersection of a semicircle with thereal axis, the bulk resistance of the polymer electrolytes can befound. The magnitude of the bulk resistance decreases withincreasing the Cr3þ concentration and this results in increase in theconductivity of the solid polymer electrolyte. The ionic conductivityof the solid polymer electrolyte was calculated using the followingformula

s ¼ lRb$A

(4)

where ‘l’ is the thickness (cm) of the polymer electrolyte, A is thearea (cm2) of the blocking electrode, and Rb is the bulk resistance ofthe solid polymer electrolyte film [34]. Cr3þ doped PEO þ PVPblended polymer electrolyte film exhibit higher ionic conductivityat 373 K in the order of 1.16 � 10�5 S/cm.

3.8.1. Temperature dependence ionic conductivityThe temperature dependent ionic conductivity plots are shown

in Fig. 9. The Arrhenius plots suggest that the ion transport in thepolymer depends on the polymer segmental motion. Fig. 9 explainsthat the ionic conduction in the polymer system obeys the Vogel-Tamman-Fulcher (VTF) relation, which describes the transportproperties in a viscous matrix. The increase in conductivity withtemperature is interpreted as being due to a hopping mechanismbetween co-ordination site, local structural relaxations andsegmental motion of polymers. The increase in conductivity withtemperature can be linked to the decrease in viscosity and hence,increased chain flexibility. In polymer electrolyte system, thechange of conductivity; with temperature can be explained by theincrease in the free volume of the system, which facilitates themigration of ions. For devices operating over a wide temperaturerange, it is desirable to have a uniform conductivity [35].

3.8.2. Dielectric analysisIn Fig. 10 shows the variation of ε0 (the real part of the complex

dielectric permittivity: ε* ¼ ε0 � j ε00) as a function of frequencies at

Fig. 7. VSM data of (a) pure PEO þ PVP (b) Cr3þ (0.025, 0.05, 0.075 & 0.1 wt%) doped PEO þ PVP blended polymer films.

Table 1Coercivity, saturation magnetization and the remanant magnetization values ofprepared polymer films.

Sample Hc (G) Ms (emu) Mr (emu)

PEO þ PVP 633.2 4.4 � 10�4 1.5 � 10�5

PEO þ PVP:Cr3þ(0.025) 344.3 7.7 � 10�4 2.9 � 10�5

PEO þ PVP:Cr3þ(0.05) 391.6 1.1 � 10�3 1.6 � 10�5

PEO þ PVP:Cr3þ(0.075) 126.6 1.8 � 10�3 5.4 � 10�6

PEO þ PVP:Cr3þ(0.1) 95.3 2 � 10�3 1.4 � 10�5

K. Naveen Kumar et al. / Journal of Molecular Structure 1100 (2015) 546e554552

different temperatures for the polymer samples incorporated withCr3þ ions. As expected, the variation tendency of dielectric constantwith frequency is the reverse of the electrical conductivity. ε0 at-tains high value at low frequency and decreases exponentially withincrease in frequency. The decrease of dielectric constant is mainlyattributed to the mis-match of interfacial polarization of compos-ites to external electric fields at elevated frequencies. The permit-tivity is enhanced near the percolation threshold. It is usually at thepercolation threshold (an important point) that the electricalproperty varies a lot. Therefore study of conducting composites inthe vicinity of percolation threshold is an effective means of

Fig. 8. ColeeCole plot of Cr3þ (0.1): PEO þ PVP blended polymer films at differenttemperatures.

Fig. 10. (a) Real and (b) imaginary plots of dielectric constants (ε0 & ε00) for Cr3þ (0.1):

PEO þ PVP blended polymer film at different temperatures.

K. Naveen Kumar et al. / Journal of Molecular Structure 1100 (2015) 546e554 553

estimating the electrical transport behaviour of composites. Thedielectric response is explained by the complex permittivityε* ¼ ε

0 � jε00, where ε

0and ε

00are the dielectric components for en-

ergy storage and energy loss of applied electric field. Dielectricproperties of ionic conducting polymers are due to the contributionof electronic, ionic, dipole orientations and space charge polariza-tions. The complex permittivity of the polymer is obtained from theimpedance data.

ε* ¼ 1

ðjuCoZ*Þ ¼ ε0 � jε

00(5)

where Z* is the complex impedance, Co is the capacitance of freemedium. The real part of the permittivity (dielectric constant ε

0

represents the polarizability, while the imaginary part (dielectricloss) ε

00 represents the energy loss due to polarization and ionicconduction. The dielectric constant ε0 is calculated from

ε0 ¼ Cd

ε0A(6)

Fig. 9. Arrhenius plot of Cr3þ (0.1) doped PEO þ PVP blended polymer film.

where C is the capacitance of the sample, ε0 is the permittivity ofthe free space (8.85� 10�12 F/m) and A is the cross-sectional area ofthe electrode [36,37].

4. Conclusions

In summary, it can be concluded that PEO þ PVP blendedpolymer films have been synthesized successfully with andwithoutCr3þ dopant ions. Their semi-crystalline natures have beenconfirmed based on XRD features and SEM images. The Ramanpeaks were appropriately assigned and analysed. Racah and crystalfield parameters B, C and Dq were evaluated from the absorptionspectrum of Cr3þ: PEOþ PVP polymer film. An intense red emissionband at 614 nm was observed under a UV excitation source whichhas been assigned to the electronic transition as 4T2g / 4A2g. Cr3þ:PEO þ PVP samples, exhibited two resonance signals with aneffective g value at g ¼ 1.99 and g ¼ 4.59. These signals areattributed to isolated Cr3þ ions and the exchange coupled Cr3þ

pairs. Cr3þ ions doped PEO þ PVP samples exhibit the super-paramagnetic hysteresis loop with a weak ferromagnetic signal inthe VSM data. In addition, these results are correlated with the EPRanalysis. The ionic conductivity values are also calculated using theimpedance analyser at different temperatures. Cr3þ (0.1wt%) dopedPEO þ PVP blended polymer displayed high ionic conductivity of

K. Naveen Kumar et al. / Journal of Molecular Structure 1100 (2015) 546e554554

1.14 � 10�5 S/cm at 373 K. Dielectric constant behaviour wasinvestigated as a function of temperature change. These polymercomposite materials were identified as potential materials forelectromagnetic device applications, such as electromagneticinterference suppression, sensors, polymer electrolytes and also asmaterials which can be used as photonic devices.

Acknowledgement

One of the authors (KNK) would like to thank the UGC, NewDelhi for award of a fellowship in the CAS programme sanctioned tothe department of Physics, Sri Venkateswara University, Tirupati,INDIA.

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