Research ArticleInfluence of the La3+, Eu3+, and Er3+ Doping on Structural,Optical, and Electrical Properties of BiFeO3 NanoparticlesSynthesized by Microwave-Assisted Solution Combustion Method

Angelika Wrzesinska,1 Alexander Khort ,2,3 Izabela Bobowska ,1 Adam Busiakiewicz,4

and Aleksandra Wypych-Puszkarz 1

1Department of Molecular Physics, Faculty of Chemistry, Lodz University of Technology, Zeromskiego 116, 90-924 Lodz, Poland2A.V. Luikov Heat and Mass Transfer Institute of the National Academy of Sciences of Belarus, 220072 Minsk, Belarus3Center of Functional Nano-Ceramics, National University of Science and Technology “MISIS”, 119049 Moscow, Russia4University of Lodz, Faculty of Physics and Applied Informatics, Department of Solid State Physics, Pomorska 149/153,90-236 Lodz, Poland

Correspondence should be addressed to Aleksandra Wypych-Puszkarz; aleksandra.wypych@p.lodz.pl

Received 30 August 2018; Accepted 4 December 2018; Published 26 March 2019

Academic Editor: Victor M. Castaño

Copyright © 2019 Angelika Wrzesinska et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work isproperly cited.

In this study, nanocrystalline (18–28 nm) perovskite-like bismuth ferrite rare earth-doped powders (Bi0.9RE0.1FeO3, where RE= La(BLaFO), Eu (BEuFO), and Er (BErFO)) were obtained by microwave-assisted modification of solution combustion synthesis(SCS). The influence of high load La3+, Eu3+, and Er3+ doping on structural, optical, and electrical properties of BiFeO3 wasinvestigated. It was found that rare earth doping along with fast phase formation and quenching significantly distorts the crystalcells of the obtained materials, which results in the formation of mixed rhombohedral- (R3c-) orthorhombic (Pbnm) crystalstructures with decreased lengths of Bi-O and Fe-O bonds along with a decreasing radius size of doping ions. This promotesreduction of the optical band gap energy and suppression of ionic polarization at high frequencies and results in enhanceddielectric permittivity of the materials at 1MHz.

1. Introduction

Bismuth ferrite BiFeO3 (BFO) is a multiferroic material,which combines ferroelectricity and ferromagnetism in thesame phase and has attracted great attention due to itspotential applications in multifunctional devices, such asdata storage systems, spintronics, and microelectronics[1–4]. Among a few known single-phase multiferroics,BFO is distinguished by its high temperature electricaland magnetic ordering (i.e., Curie temperature TC = 810 –830°C [5] and Neel temperature TN = 370°C [6]). Becauseof these features and good optical properties [7, 8], pureand doped BFO are considered highly promising candidatesfor practical applications in next-generation smart materials.

At room temperature, BFO has a rhombohedral distortedperovskite structure with the R3c space group [9]. This

structure can be obtained from a cubic parent perovskite byrotations of the oxygen octahedra around the 111 cdirection and displacements of Bi3+ and Fe3+ cations alongthe same c direction. Fe3+ ions are in the distorted oxygenoctahedra, while Bi3+ ions, occupying the dodecahedralpositions, are strongly shifted from the central positiontowards one of Fe3+ ions due to the lone pair effect [10, 11].At around 825°C, BFO has a strong first-order transitionfrom a rhombohedral to an orthorhombic structure (Pbnmsymmetry) with attendant unit cell shrinks [5, 12].

Recently, much attention has been paid to understand theeffect of chemical composition [13–16], pressure [17, 18],temperature of the synthesis, and annealing [19, 20] oncrystal structure and physical properties of BFO-based nano-powders. A number of studies reported strong dependence ofBFO electromagnetic properties from its nanoscale structure

HindawiJournal of NanomaterialsVolume 2019, Article ID 5394325, 11 pageshttps://doi.org/10.1155/2019/5394325

[21, 22]. For example, high-resolution neutron diffractionstudies have shown that the magnetic order of BFO is antifer-romagnetic with G-type cycloid spin configuration with aperiod of 62 nm [23, 24]. Magnetization exhibits highervalues with a decrease of particle sizes, which is correlatedto the higher suppression of its spin cycloid incommensurateto particle size. In addition, RE-ion (RE rare earth ion)doping is an easy way to enhance ferroelectric [25–27] andoptical properties of BFO-based materials (increase dielectricconstant, decrease optical band gap, etc.), which is cruciallyrequired for the creation of a new type of functional materialsfor application in multiple devices [28, 29]. Doping byRE-ions gives a great possibility to control physical proper-ties of BFO-based materials by varying their nanoscalestructure, and due to this feature, it is a subject of numerousongoing and future studies.

Numerous synthesis techniques, such as hydrothermal,coprecipitation, molten-salt, thermal decomposition, andsol-gel [30–35], have been developed to obtain doped andneat BFO nanoparticles. Among them, a variety of modifiedsolution combustion methods have several advantages: lowinitialization temperature, fast kinetics of reaction, andhomogeneous powder with very fine particles [36–38]. In thispaper, we studied the effect of high load RE doping on struc-ture, phase composition, and electrical and optical propertiesof BFO nanomaterials, prepared by microwave-assistedmodification of solution combustion synthesis (SCS) aimingthe creation of ferroelectric nanomaterial with enhancedproperties for photocatalysis and photovoltaic devices.Microwave heating ensures a homogeneous increase oftemperature in the reagent mixture and preparation of theuniform precursor for a combustion step of synthesis. Thesecause fast-phase formation and significantly affect crystalstructure and properties of the materials.

2. Experimental

2.1. Synthesis Procedure. All used chemicals had analyticalpurity and were purchased from Speckhimteh Ltd. (Russia).Perovskite-like structured bismuth ferrites, i.e., neat (BFO)and rare earth-doped (Bi0.9RE0.1FeO3, where RE=La (BLaFO),Eu (BEuFO), and Er (BErFO)) powders were synthesized bymicrowave-assisted modification of SCS using stoichiomet-ric mixtures of metal nitrates (oxidizer) with fuel (reducer).Bismuth(III)-nitrate pentahydrate (Bi(NO3)3⋅5H2O) andiron(III)-nitrate nonahydrate (Fe(NO3)3⋅9H2O) were usedas the main raw materials. Lanthanum(III)-nitrate hexahy-drate (La(NO3)3⋅6H2O), europium(III)-nitrate hexahydrate(Eu(NO3)3⋅6H2O), and erbium(III)-nitrate hexahydrate(Er(NO3)3⋅6H2O) were chosen as the sources of RE dopingions. Citric acid (CA) was used as a fuel component. Thecombustion reactions take place according to the schemesuggested in:

3‐x Bi NO3 3 + xRE NO3 3 + 3Fe NO3 3+ 5φC6H8O7 + 22 5 φ − 1 O2

⟶ 3Bi1‐xRExFeO3 + 30φCO2 + 9N2 + 20φH2O1

The parameter φ, the fuel to oxidizer ratio, is definedsuch that φ = 1 corresponds to a stoichiometric oxygen con-centration, meaning that the initial mixture does not requireatmospheric oxygen for complete oxidation of the fuel,while φ > 1 (<1) implies fuel-rich (or lean) conditions. Inthe case of φ > 1, the protective atmosphere is formed fromthe oxidation products of the fuel.

For all experiments, the ratio φ between the fuel and theoxidizer was kept constant and equal to 1.25. According toour preliminary research, the chosen fuel to oxidizer ratioprovides optimal conditions for the preparation of highlydispersed BFO nanoparticles with a minimal content ofsecondary phases.

All the samples were synthesized by the microwave-assisted SCS method, applied earlier for metallic nanopow-der synthesis [39–41]. In general, bismuth(III)-nitrate pen-tahydrate with 2% excess and CA were dissolved in aminimum volume of acidic aqueous solution in order toprevent bismuth subnitrate precipitation. Iron(III)-nitratenonahydrate was dissolved in a minimum amount of twicedistilled water. Then these solutions were mixed togetherand rapidly dried in a microwave oven (800W,2.450GHz—maximal working parameters of our oven)until gel formation, and then foam was formed. Micro-wave heating causes rapid water evaporation from a bulkof solutions and very fast production of large quantity ofsteam; then foam formation occurs that is preferred forself-combustion synthesis. The foam was ignited and burntin thermal explosion mode in a preheated 300°C mufflefurnace, leading to the formation of a brown fluffy pow-der. The obtained powder was grinded and annealed inair at 650°C for 30min with rapid heating and coolingby means of quenching. After annealing, the obtainedpowders were grinded one more time.

2.2. Characterization. X-ray diffraction (XRD) measure-ments in the Bragg–Brentano reflection geometry weredone at room temperature (21°C) using a PANalyticalX’Pert Pro MPD diffractometer with copper CuKα radiation(λ = 1 5406Å). Diffractograms were recorded with a 0.0167o

step at an exposure time of 20 s. The powder samples werespun during measurements to decrease preferred orientationeffects. The phase analysis was performed by a comparison ofpeak positions and relative intensities of obtained XRD datawith standard reference materials from the InternationalCentre for Diffraction Data (JCPDS) powder diffraction(PDF-2 ver. 2009) database. The obtained diffraction datawere refined using the Rietveld method in the PANalyticalHigh Score Plus software package. The pseudo-Voigtfunction was used for the peak profile refinement.

The average crystallite size of obtained samples wascalculated using the Scherrer formula:

D = kλβ cos θ , 2

where D is the mean size of the crystallite, k is a dimension-less shape factor (with a typical value of 0.9), λ is the X-ray

2 Journal of Nanomaterials

wavelength, β is the line broadening at the half of themaximum intensity, and θ is the Bragg angle (in degrees).

Raman investigations were performed using a JobinYvonT64000 triple-grating Raman spectrometer equipped with anOlympus BX40 confocal microscope. The Argon laser withλ = 514 5 nm wavelength was used for sample excitation.Acquisition time was 400 s for each spectrum.

Absorption FT-IR spectra were measured by a ThermoScientific Nicolet iS50 Infrared Spectrometer. Spectra wererecorded in a far infrared range (FIR) of 300–600 cm-1 usingthe attenuated total reflection (ATR) accessory with adiamond crystal.

The morphology of the samples was studied usingscanning electron microscopy (SEM) with a Vega 5135MM Tescan instrument equipped with secondary electronand backscattered electron detectors and an Oxford Instru-ments Link 300 ISIS system for energy dispersive X-ray(EDX) microanalysis.

The reflectance measurements of pelleted samples werecarried out by UV-Vis-NIR spectrometry (Varian Inc., Carry5000 spectrometer), using an integrating sphere. The scanswere conducted in a 350–700nm range.

The dielectric response measurements were carried outusing a Novocontrol GmbH Concept 40 broadband dielectricspectrometer equipped with a Quatro Cryosystem in thefrequency range of 10–1 ÷ 106 Hz. For measurements, allsynthesized powders were hydraulically pressed with a press-ing force of 4000 kg for 5min to form pellets (diameter~13mm and high ~0.9mm). To improve the contactbetween the sample and external electrodes during measure-ments, 150 nm thick gold electrodes were deposited on bothsides of the pellets. Before measurements, all pelleted sampleswere dried at 90°C in a vacuum to eliminate the influence ofthe humidity.

3. Results and Discussion

Figures 1(a) and 1(b) illustrate SEMmicrographs at a magni-fication of ×10k and EDX spectra of all the samples. The neatBFO sample is characterized by homogenous sphericalcrystalline aggregates with an average size varying from100nm to 500nm. The sample BEuFO has less regular shapeof grains; however, the mean size is lower than that for BFO.The BLaFO and BErFO samples are distinguished by hetero-geneous morphology composed of fine grains and flakyparticles of a micrometer size. The results of EDX analysisconfirm the presence of rare earth elements in the dopedsamples. The quantitative data presented in the tables(Figure 1(b)) indicate the approximate element ratio that isin agreement with an expected amount of doping, i.e.,Bi0.9RE0.1FeO3.

XRD patterns of BFO, BLaFO, BEuFO, and BErFOsamples are presented in Figure 2. The main crystalline phasein all samples is BiFeO3 with a distorted perovskite structure.In addition, diffraction peaks of secondary phases, such asBi2Fe4O9, α-Bi2O3, and β-Bi2O3, were indexed. The presenceof the secondary phases could be due to the local heterogene-ity of the high-temperature combustion process of a foamedprecursor [42]. After the precursor starts to combust,

temperature locally reaches very high values. As bismuth isinclined to sublimation, it can evaporate from hotter regionsand condense on colder surfaces, creating a local concentra-tion gradient. Moreover, no additional diffraction peaksrelated to secondary RE-based phases have been observed,implying good solubility of high load RE ions in the BFOcrystal lattice.

Figure 2(b) shows the enlarged view of the doublet peakscorresponding to the (104) and (110) planes around 2θ ~32°.According to the literature data [43, 44], RE doping leadsto a slight shift of both peaks to higher 2θ values, whichcould even merge into a single peak due to partial phasetransition from a rhombohedral (R3c) to an orthorhombic(Pbnm) structure. The main reason of such peaks’ shift isthe substitution of Bi3+ by smaller size RE ions, whichreduces cell parameters. The partial structural transitioncan produce a distortion of the FeO6 octahedron due tothe changes in the Fe–O bond length and O–Fe–O bondangles, affecting the electrical properties of BiFeO3. In ourcase, Bi3+ is substituted by close in size La3+ and smallerEu3+ and Er3+ ions (rBi

3+ion = 1 03Å, rLa

3+ion = 1 03Å, rEu

3+ion =

0 95Å, and rEr3+

ion = 0 89Å, respectively).Calculated Rietveld refined XRD parameters for all syn-

thesized materials are summarized in Table 1. The BFO andBLaFO samples have quite similar unite cell parameters.Due to close ionic radii, substitution of Bi3+ by La3+ ions inthe BFO crystal structure does not strongly affect the posi-tions of (104) and (110) peaks. At the same time, it can benoticed that the (110) peak of the BFO sample is significantlysmaller than the (104) peak, unlike the peaks of the BLaFOsample. The ratio of the areas of the (104) peak to the (110)peak for BFO is 2.731, which is much higher than that forBLFO (0.522). In this case, a higher ratio of the peak areasindicates a higher degree of R3c to Pbnm structure transition.We suppose that the La doping did not significantly affect theperovskite structure. At the same time, the structure of theundoped sample was slightly changed due to the partial“freezing” of the high-temperature phase shift as a resultof fast phase formation during combustion reaction andfollow-up quenching.

In the case of the Eu-doped sample, the shrinkage ofall cell parameters is clearly seen. Both (104) and (110)peaks are shifted to higher 2θ angles of 32.09° and32.23°, respectively (Figure 2(b)). It can be also noticedthat the (110) peak is almost suppressed and merged withthe (104) peak (ratio of the peaks’ areas is 8.803). Thisclearly indicates a very high degree of rhombohedral toorthorhombic structure transition.

In the BErFO sample, two separate perovskite BiFeO3crystal phases (low-temperature R3c and high-temperaturePbnm) were found. Positions of (104) and (110) peaks ofthe R3c phase are shifted to 31.89° and 32.28°, respectively,and their areas’ ratio is 1.158, which indicates a low degreeof structural transition. Obviously, due to the high differencein the ionic radii of Bi3+ and Er3+ (~14%), the effect of Erdoping on the perovskite structure of bismuth ferrite is sosignificant that the structure distortion promotes theappearance of the two separate phases. Such a combination

3Journal of Nanomaterials

5 �휇m

5 �휇m

5 �휇m

5 �휇m

(a)

ElmtO KFe KEr LBi M

Bi

BiO Fe

FeFe

Fe

Fe

Fe Fe

FeLa

LaFe

Fe

EuEu

EuEu

O

O

O

FeEr ErBi

Bi

Bi

Bi

Bi

Bi Bi

BiBiBi

Bi

BiBi

Bi Bi BiBi

Bi Bi

00

5

10

15

20

25

cps

0

5

10

15

20

25cps

0

5

10

15

20

25cps

0

5

10

15

20cps

5 10 15

Energy (keV)

20

0 5 10 15

Energy (keV)

20

0 5 10 15

Energy (keV)

20

0 5 10

Energy (keV)

Elem. %30.9913.724.7150.59

Atomic %78.9710.011.159.87

ElmtO KFe KEu LBi M

Elem. %32.0917.073.8447.00

Atomic %78.3011.930.998.78

ElmtO KFe KLa LBi M

Elem. %35.3713.392.8548.38

Atomic %81.808.870.768.57

ElmtO KFe KRe LBi M

Elem. %24.7619.4−56.20

Atomic %71.7315.80−12.47

(b)

Figure 1: (a) SEM images at a magnification of ×10k and (b) EDX spectra with results of elemental analysis of BFO, BLaFO, BEuFO, andBErFO samples. (SEM images and corresponding EDX data are placed in one row.)

4 Journal of Nanomaterials

012

012

104

110

113 00

6 202

024

211 116

122

018 21

403

0

012 10

4 110

113 00

6 202

202

024

211 11

612

2

018 21

403

0

012

20 30 40

2�훩

50 60

104

110

113 00

6 024

211 11

612

2 018 21

403

0

002

111

002 1

04 200

110

113 00

620

2

220 02

4

211

116 2

2212

2 018 21

403

0

- Bi2Fe4O9

- �훽 − Bi2O3

- �훼 − Bi2O3 CalculatedDifference

Observed

(a)

2�훩

31.0

(104) (110)

(104) (110)

(104)

(110)

(104)

(020)

(200)

(110)

31.5 32.0 31.5 33.0

BErFO

BEuFO

BLaFO

BFO31.77º

32.06º

32.03º32.75º

32.09º

32.23º

32.28º31.85º

31.89º 32.19º

(b)

Figure 2: Results of XRD analysis of BFO, BLaFO, BEuFO, and BErFO samples: (a) Rietveld refined XRD patterns and (b) enlargedview of the diffraction peaks around 32° 2θ range with doublet peaks (104) and (110), simulated with Lorenz function, showing peakshift and splitting.

Table 1: Rietveld refined XRD parameters for neat and doped BFO.

SamplesBFO BLaFO BEuFO BErFO

Parameters

Space group R3c R3c R3c R3c Pbnm

a (Å) 5.584 5.583 5.570 5.593 5.538

b (Å) 5.584 5.583 5.570 5.593 5.594

c (Å) 13.853 13.853 13.654 13.384 7.843

Volume (Å3) 374.07 373.99 366.96 362.61 242.96

Content of the main phase (wt.%) 91.2 90.3 90.5 90.2

Content of Bi2Fe4O9 (wt.%) 4.1 4.3 2.8 7.6

Content of Bi2O3 (wt.%) 4.7 5.4 6.7 2.2

Rp 6.01 5.18 5.64 6.21

Rw 8.10 6.39 6.80 7.38

Goodness of fit 0.74 1.05 1.12 2.01

5Journal of Nanomaterials

of phases, apparently, is more energy-efficient at room tem-perature than only one highly distorted structure.

In all cases, the observed merging of the peaks indi-cates rhombohedral to orthorhombic phase transition, highenough to affect electrical and optical properties of BFO-based materials.

The average crystallite sizes were calculated for the mainpeak (110) of all the samples and found to be about 17nm forthe neat BFO sample and 28nm, 18nm, and 18nm forBLaFO, BEuFO, and BErFO samples, respectively. Theobserved decrease in size is typical for RE-doped materials[43, 44]. However, crystalline sizes of the materials, preparedby our modified method, are quite lower in the comparisonof grain sizes of bismuth ferrites synthesized by othermethods. It could be due to the application of intense micro-wave drying, which provides formation of homogenousfoams with high surface areas. The foams promote follow-up fast SCS reaction, which starts at low temperature practi-cally simultaneously in the whole reacting volume and endsin a very short time (~5–10 s). This excludes necessity of longtime high-temperature calcination to remove traces of a fueland prevents intense growth of crystalline sizes. Moreover,fast SCS in an explosion mode along with postsynthesis heattreatment with follow-up quenching could be another reasonof mixed phase formation in RE-doped bismuth ferrites withhighly distorted crystal cells.

The Raman spectra of neat and doped BFO samples areshown in Figure 3. Raman spectroscopy is sensitive to thechange in the crystal structure of the investigated materials;thus, this technique allows better understanding of thestructural modifications induced by the substitution of Bi3+

by lanthanide ions. Obtained results are in good agreementwith literature-reported spectra of rhombohedral BFO[42, 45, 46]. Based on a group theory, neat BFO with arhombohedral lattice system (R3c space group) is character-ized by 13 Raman active modes represented by Г = 4A1 + 9E.In the present research, BFO peaks at 139 cm-1, 211 cm-1,273 cm-1, and 445 cm-1 were assigned to A1 modes. E-typeRaman modes were observed at 121 cm-1, 312 cm-1,375 cm-1, and 386 cm-1. The low-frequency A1 and some ofE (TO) modes are assigned to the Bi-O bonds, while E(TO) modes, which appear in a higher Raman shift region,are attributed to Fe–O bonds [47]. With the decrease ofdoping ionic radii, one can observe band movement tothe higher Raman shift positions which is connected withdecreasing of the Bi-O bond length [48]. The variation inthe vibrational modes of doped samples in comparison toneat BFO is clearly visible. The observed peak shift andbroadening accompanied with the variation of their inten-sity clearly show structural transition that was substantiatedby the XRD study.

FTIR spectra recorded in the range of 300–600 cm-1 inthe absorbance mode for all synthesized materials are shownin Figure 4. There are typical band characteristics of metaloxygen bonds. Two strong absorption peaks observed near436 cm-1 and 536 cm-1 were assigned to the Fe–O bendingand stretching vibrations in the FeO6 octahedral groups inthe BFO perovskite structure, respectively [49, 50]. Twoother weak peaks around 380 cm-1 and 477 cm-1 are due to

the presence of Bi–O bonds in BiO6 octahedra along withthe FeO6 group [51–53]. In addition, in the case of the BErFOsample, the peak split is observed around 536 cm-1, whichindicates the presence of two separate perovskite phases inthis sample.

In addition, FTIR spectra reveal the softening of vibrationmodes in a row of BLaFO–BFO–BEuFO–BErFO, which isdue to the concomitant structural R3c–Pbnm phase transi-tions as confirmed by the XRD analysis. However, no signif-icant shift of absorption bands in doped samples wasobserved, due to 10mol% doping by RE elements, which isin good agreement with literature data [49].

Figure 5 shows the absorbance vs. wavelength plot of neatand doped samples derived from diffuse reflectance data. Thestrong band at 450–600nm is attributed to a metal-metaltransition, and the weak peak at ~700nm is assigned to thecrystal field transition.

100

121139

211273

312375 386

445 BFO

BLaFO

BEuFO

BErFO

150 200 250 300Raman shift (cm−1)

Inte

nsity

(a.u

.)

350 400 450 500

Figure 3: Raman scattering spectra of neat and RE-doped BFOnanomaterials in the range of 80-500 cm-1.

BFO

Bi−OFe−O Bi−O

Fe−O532

380469 477

539

549

BLaFO

BEuFO

BErFO

300

Wavenumber (cm−1)

Abso

rban

ce (a

.u.)

350 400 450 500 550 600

Figure 4: FTIR spectra of neat and RE-doped BFO nanopowders inthe range of 300-600 cm-1.

6 Journal of Nanomaterials

The Kubelka-Munk function was used to calculate theoptical absorption coefficient (α) from the reflectance dataas follows:

a = 1 − R 2

2R , 3

where R is the measured reflected light. Band gap values forall samples can be determined using the formula:

αhv = B hv − Egn, 4

where hν is the incident photon energy, α is the absorptioncoefficient, B is the absorption edge width parameter, Eg isthe band gap, and n is the exponent dependent on directand indirect transition across the band gap.

Extrapolation of the linear region of the αhν 2 vs. E (eV)plot to the intersection with the x-axis provides accuratedetermination of the optical band gap energy (Eg) values(linear extrapolation of the Tauc method) (Figure 6). ForBFO material, determined optical band gap energy corre-sponds to the energy difference between the top of the O 2pvalence band and bottom of the Fe 3d conduction band[54]. The obtained Eg value for BFO is 2.02 eV and is in goodagreement with previously reported values being in a range ofca. 1.8–2.8 eV [55–57]. The lower band gap energy valuecould be explained by the smaller size of crystallites ofobtained BFO as reported in the literature [42, 54, 58, 59].The substitution of Bi3+ by RE ions in BFO determined anoticeable decrease in the optical band gap energy to 1.96,1.93, and 1.94 eV for BLaFO, BEuFO, and BErFO, respec-tively, which are lower than those previously reported[54–60]. There might be several explanations of the observedreduced band gap in the doped BFO samples. As it was men-tioned before, crystalline size reduction can cause decreased

optical band gap energy. Besides, the bond lengths directlyeffect on electron bandwidth (W) and, hence, band gap ofthe obtained materials. The band gap reduction in dopedBFO samples is possible due to lattice contractions, result-ing from reducing of Fe-O and Fe-O-Fe bond lengths[7, 54, 60, 61]. As reported elsewhere [54, 60], W hasan inverse dependence from Fe-O bond length and Eg is con-nected to W as Eg = Δ –W, where Δ is the charge transferenergy. Thus, decreasing Fe-O bond length with the incorpo-ration of rare earth ions into BFO structure may considerablyincrease W values and, consequently, reduce Eg. To sum up,optical measurements showed the reduction of band gap withrare earth ion doping, which increases the absorption capa-bility of the obtained materials in visible range and, in turn,broadens their possible applications in photocatalysis andphotovoltaic devices.

To investigate the dielectric properties of neat anddoped BFO samples, broadband dielectric spectroscopywas applied. Figures 7 and 8 show variation of the real partof dielectric permittivity (ε′) and loss tangent (tan δ) asthe function of frequency in the range of 0.7Hz–6.5MHzat 30°C.

The dispersive behavior is observed for all the samples inthe whole frequency range for both ε′ and tan δ representa-tions. The dielectric permittivity dispersion is associated withfour fundamental different mechanisms of polarization, andeach of them dominates at different frequencies. At lowerfrequencies, dipolar and interfacial polarization plays animportant role in the dielectric behavior of BFO materials,whereas at higher frequencies, the main contribution in ε′is due to the electronic and ionic polarizations [62].As dielectric media consists of poorly conductive grainboundaries and well conductive crystallites, a space charge

BFO

Wavelength (nm)400

Abs

orba

nce (

a.u.)

0.8

0.9

1.0

500 600 700

BLaFOBEuFOBErFO

Figure 5: UV-Vis absorption spectra of neat and doped BFOnanomaterials in the range 350-700 cm-1.

BFO

2.0 2.02.5

2.0

Eg = 2.02

Eg = 2.11 Eg = 2.01

Eg = 1.93

2.5

E (eV)

(�훼h�휐

)2 (a.u

.)

2.0 2.5

2.5

BLFO

BGFOBEFO

Figure 6: αhν 2 vs. photon energy, hν, plot to calculate band gapenergy of the neat and doped BFO samples.

7Journal of Nanomaterials

polarization occurs at low frequencies as an effect of theheterogeneity of the material structure that subsequentlyincreases dielectric permittivity values. As frequencyincreases, an additional contribution becomes dominantdue to electrons hopping between Fe3+ and Fe2+ ions atFeO6 octahedra sites [24, 60]. The latter is connected withdipole rotation in the field direction. The influence of polari-zation and its relaxation on ε′ becomes less perceptible as fre-quencies increase because of inertia of charge movement. Afurther frequency increase leads to the decrease of dielectric

permittivity, which finally becomes frequency-independent[43]. Similar to the optical properties, the electric propertiesof synthesized nanomaterials have been found to be greatlyinfluenced by the structural changes as a result of dopingand features of the synthesis process. The dielectric value aswell as dielectric dispersion increases in a row of BLaFO–BErFO–BFO–BEuFO, which is in good agreement with thepolarization theory and structure of obtained samplesrevealed by XRD, Raman, and FTIR data. At low frequencies,ε′ values are mostly influenced by the amount of hoppingelectrons between Fe3+ and Fe2+ ions, which is the highestin the Eu-doped sample due to a highly distorted perovskitecrystal structure. Obviously, the polarization through thismechanism should be higher when the greater differencein the dimensions of the ionic radii between Bi3+ andRE3+ ions is observed. However, this rule does not workwhen energy stabilization occurs through formation oftwo phases due to very high distortion of crystal structure(BErFO sample in this work). In this case, one of thesephases is paraelectric and does not contribute much to avalue of dielectric permittivity and dispersion. On the otherhand, BFO has a high enough distorted structure due tofast phase formation and quenching to show a high valueof permittivity and dielectric dispersion.

At higher frequencies, the contribution of dipolepolarization and interfacial polarization decreases, as wellas reduction of ε′, becomes less significant for all samples.Nevertheless, it could be noticed that frequencies higher than~105Hz correlation of permittivity values switch to theopposite side (i.e., the highest ε′ value for La-doped and neatBFO and the lowest one for BEuFO). At 1.15MHz frequency,the real part of the dielectric permittivity was 41, 38, 34, and36 for BLaFO, BFO, BEuFO, and BErFO, respectively. Wesuppose that the main reason of this switch is due to thesuppression of ionic polarization of the distorted perovskitecrystal structure at high frequencies. This assumption isconfirmed by tan δ data. At low frequencies, tan δ is affectedby dipole polarization and changes in a similar order like ε′representation for all investigated samples. At about 105Hz,there is an obvious abrupt change in gradient of loss tangentcurves of BLaFO, which indicates change in polarizationmechanism, as dipole polarization becomes negligible andionic polarization does not affect dielectric loss. On the otherhand, a very slight change in the gradient of tan δ for BFO,BEuFO, and BErFO samples is observed. Thus, ionic polari-zation is suppressed considerably for neat and Eu- andEr-doped samples due to a high degree of distortion of theirstructure while less suppressed for the BLaFO sample. Thissuppression might be caused by the change of Fe–O lengthbond, which obstructs ionic polarization, and by the decreaseof the amount of oxygen vacancies.

Other factors influencing the ε′ and tan δ values are grainsizes and sample morphology, i.e., polydispersity of grain’ssize [63]. We suppose that lower grain sizes promote dipolemobility at high frequencies through the change of theamount of domain boundaries. However, low concentrationof secondary phases did not significantly affect dielectricbehavior in all investigated samples.

100

1000

100

101 100 102

Frequency (Hz)

Frequency (Hz)

Die

lect

ric p

erm

ittiv

ity, (�휀′)

Die

lect

ric p

erm

ittiv

ity, (�휀‵)

104 105 106

10530

35

40

45

106

BFOBLaFO

BEuFOBErFO

Figure 7: Frequency dependence of real-part dielectric permittivityat 30°C of neat and codoped BFO materials. The insert shows theenlarged view of the dielectric permittivity curves in the frequencyrange of 1 ⋅ 105 ÷ 3 ⋅ 106 Hz.

100

10

1

0.1

101 100 102

Frequency (Hz)

Frequency (Hz)Loss

tan

Loss

tan

104 105 106

1050.05

0.10

0.15

0.20

0.25

106

BFOBLaFO

BEuFOBErFO

Figure 8: Frequency dependence of loss tangent at 30°C of neat andcodoped BFO materials. The insert shows the enlarged view of theloss tangent curves in the frequency range of 1 ⋅ 105 ÷ 3 ⋅ 106 Hz.

8 Journal of Nanomaterials

4. Conclusions

In this study, we investigated the effect of high loadLa3+, Eu3+, and Er3+ doping on structural, optical, andelectrical properties of nanocrystalline BiFeO3 obtained bymicrowave-assisted modification of solution combustionsynthesis. The combination of features of our modified SCSmethod and high load of RE doping results in significantdistortion of crystalline cells of the obtained bismuthferrite nanopowders with follow-up formation of mixedrhombohedral-orthorhombic crystal structures, which wasconfirmed by the results of XRD, Raman spectrometry, andFTIR analysis. The highest degree of distortion of crystallineparameters was found in Eu-doped samples. At the sametime, high load Er doping led to the formation of doped bis-muth ferrite in two polymorph structures, as a result ofenergy relaxation. It was found that the observed cell distor-tion as well as the decrease of crystalline sizes affects opticaland electrical properties of the BFO-based materials. Theoptical band gap energy was decreased from 2.02 eV to1.96-1.93 eV for neat BFO and RE-doped samples, respec-tively, that makes obtained materials promising candidatesfor photocatalytic and photovoltaic devices. Performed stud-ies showed that microwave-assisted solution combustionsynthesis is a favorable method to prepare a broad varietyof neat and doped nanomaterials. Such method allows usa fast and efficient way to adjust properties of nanomater-ials by its doping.

Data Availability

The data that support the findings of this study are availablefrom the corresponding author, AWP, upon reasonablerequest.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Acknowledgments

The authors gratefully acknowledge the financial support ofthe Ministry of Education and Science of the Russian Feder-ation in the framework of Increase Competitiveness Programof NUST “MISiS,” implemented by a governmental decreedated at the 16th of March 2013, N 211, and the Ministryof Science and Higher Education of the Republic of Polandno. 8862/E-370/S/2018.

References

[1] Y. Tokura, “Materials science: multiferroics as quantum elec-tromagnets,” Science, vol. 312, no. 5779, pp. 1481-1482, 2006.

[2] M. Bibes and A. Barthelemy, “Multiferroics: towards amagnetoelectric memory,” Nature Materials, vol. 7, no. 6,pp. 425-426, 2008.

[3] W. Eerenstein, N. D. Mathur, and J. F. Scott, “Multiferroicand magnetoelectric materials,” Nature, vol. 442, no. 7104,pp. 759–765, 2006.

[4] K. F. Wang, J. M. Liu, and Z. F. Ren, “Multiferroicity: the cou-pling between magnetic and polarization orders,” Advances inPhysics, vol. 58, no. 4, pp. 321–448, 2009.

[5] D. C. Arnold, K. S. Knight, F. D. Morrison, and P. Lightfoot,“Ferroelectric-paraelectric transition in BiFeO3: crystal struc-ture of the orthorhombic β phase,” Physical Review Letters,vol. 102, no. 2, 2009.

[6] A. I. Klyndyuk and A. A. Khort, “Thermophysical propertiesof BiFeO3, Bi0.91Nd0.09FeO3, and BiFe0.91Mn0.09O3 multifer-roics at high temperatures,” Physics of the Solid State, vol. 58,no. 6, pp. 1285–1288, 2016.

[7] A. D. Mani and I. Soibam, “Dielectric, magnetic and opticalproperties of (Bi,Gd)FeO3- Ni0.8Zn0.2Fe2O4 nanocompos-ites,” Ceramics International, vol. 44, no. 2, pp. 2419–2425, 2018.

[8] N. Gao, C. Quan, Y. Ma et al., “Experimental and firstprinciples investigation of the multiferroics BiFeO3 andBi0.9Ca0.1FeO3 : structure, electronic, optical and magneticproperties,” Physica B: Condensed Matter, vol. 481, pp. 45–52, 2016.

[9] J. G. Park, M. D. Le, J. Jeong, and S. Lee, “Structureand spin dynamics of multiferroic BiFeO3,” Journal ofPhysics. Condensed Matter, vol. 26, no. 43, article 433202,2014.

[10] P. Fischer, M. Polomska, I. Sosnowska, and M. Szymanski,“Temperature dependence of the crystal and magnetic struc-tures of BiFeO3,” Journal of Physics C: Solid State Physics,vol. 13, no. 10, pp. 1931–1940, 1980.

[11] J. D. Bucci, B. K. Robertson, and W. J. James, “The precisiondetermination of the lattice parameters and the coefficientsof thermal expansion of BiFeO3,” Journal of Applied Crystal-lography, vol. 5, no. 3, pp. 187–191, 1972.

[12] R. Palai, R. S. Katiyar, H. Schmid et al., “β phase and γ−βmetal-insulator transition in multiferroicBiFeO3,” PhysicalReview B, vol. 77, no. 1, 2008.

[13] B. Ahmmad, K. Kanomata, K. Koike et al., “Large differencebetween the magnetic properties of Ba and Ti co-dopedBiFeO3 bulk materials and their corresponding nanoparticlesprepared by ultrasonication,” Journal of Physics D: AppliedPhysics, vol. 49, no. 26, article 265003, 2016.

[14] G. S. Arya and N. S. Negi, “Effect of In and Mn co-doping onstructural, magnetic and dielectric properties of BiFeO3 nano-particles,” Journal of Physics D: Applied Physics, vol. 46, no. 9,article 095004, 2013.

[15] K. Brinkman, T. Iijima, and H. Takamura, “Acceptor dopedBiFeO3ceramics: a new material for oxygen permeation mem-branes,” Japanese Journal of Applied Physics, vol. 46, no. 4,pp. L93–L96, 2007.

[16] I. Coondoo, N. Panwar, I. Bdikin, V. S. Puli, R. S. Katiyar,and A. L. Kholkin, “Structural, morphological and piezore-sponse studies of Pr and Sc co-substituted BiFeO3 ceramics,”Journal of Physics D: Applied Physics, vol. 45, no. 5, article055302, 2012.

[17] Z.-W. Chen, J.-S. Lee, T. Huang, and C.-M. Lin, “Phasetransitions of pure and Ba-doped BiFeO3 under high pres-sure,” Solid State Communications, vol. 152, no. 16, pp. 1613–1617, 2012.

[18] R. Haumont, J. Kreisel, and P. Bouvier, “Raman scattering ofthe model multiferroic oxide BiFeO3: effect of temperature,pressure and stress,” Phase Transitions, vol. 79, no. 12,pp. 1043–1064, 2006.

9Journal of Nanomaterials

[19] N. A. Lomanov andV. V. Gusarov, “Influence of synthesis tem-perature on BiFeO3 nanoparticles formation,” Nanosystems:Physics, Chemistry, Mathematics, vol. 4, pp. 696–705, 2013.

[20] G. F. Cheng, Y. J. Ruan, W. Liu, and X. S. Wu, “Effect oftemperature variation on the phase transformation in thereaction sintering of BiFeO3 ceramics,” Materials Letters,vol. 143, pp. 330–332, 2015.

[21] T. J. Park, G. C. Papaefthymiou, A. J. Viescas, A. R.Moodenbaugh, and S. S. Wong, “Size-dependent magneticproperties of single-crystalline multiferroic BiFeO3 nanoparti-cles,” Nano Letters, vol. 7, no. 3, pp. 766–772, 2007.

[22] S. M. Selbach, T. Tybell, M.-A. Einarsrud, and T. Grande,“Size-dependent properties of multiferroic BiFeO3 nanopar-ticles,” Chemistry of Materials, vol. 19, no. 26, pp. 6478–6484, 2007.

[23] M. Hasan, M. F. Islam, R. Mahbub, M. S. Hossain, and M. A.Hakim, “A soft chemical route to the synthesis of BiFeO3nanoparticles with enhanced magnetization,” MaterialsResearch Bulletin, vol. 73, pp. 179–186, 2016.

[24] A. Jaiswal, R. Das, K. Vivekanand, P. Mary Abraham,S. Adyanthaya, and P. Poddar, “Effect of reduced particle sizeon the magnetic properties of chemically synthesized BiFeO3nanocrystals,” The Journal of Physical Chemistry C, vol. 114,no. 5, pp. 2108–2115, 2010.

[25] P. Suresh, P. D. Babu, and S. Srinath, “Role of (La, Gd)co-doping on the enhanced dielectric and magnetic propertiesof BiFeO3 ceramics,” Ceramics International, vol. 42, no. 3,pp. 4176–4184, 2016.

[26] S. Madolappa, S. Kundu, R. Bhimireddi, and K. B. R. Varma,“Improved electrical characteristics of Pr-doped BiFeO3ceramics prepared by sol–gel route,” Materials ResearchExpress, vol. 3, no. 6, 2016.

[27] B. Yotburut, T. Yamwong, P. Thongbai, and S. Maensiri,“Synthesis and characterization of coprecipitation-preparedLa-doped BiFeO3nanopowders and their bulk dielectricproperties,” Japanese Journal of Applied Physics, vol. 53,no. 6S, article 06JG13, 2014.

[28] P. Kumar, C. Panda, and M. Kar, “Effect of rhombohedral toorthorhombic transition on magnetic and dielectric propertiesof La and Ti co-substituted BiFeO3,” Smart Materials andStructures, vol. 24, no. 4, article 045028, 2015.

[29] R. Das, G. G. Khan, S. Varma, G. D. Mukherjee, andK. Mandal, “Effect of quantum confinement on optical andmagnetic properties of Pr–Cr-codoped bismuth ferrite nano-wires,” The Journal of Physical Chemistry C, vol. 117, no. 39,pp. 20209–20216, 2013.

[30] G. Dhir, P. Uniyal, and N. K. Verma, “Sol–gel synthesizedBiFeO3 nanoparticles: enhanced magnetoelelctric couplingwith reduced particle size,” Journal of Magnetism and Mag-netic Materials, vol. 394, pp. 372–378, 2015.

[31] J. Wang, Y. Wei, J. Zhang, L. Ji, Y. Huang, and Z. Chen,“Synthesis of pure-phase BiFeO3 nanopowder by nitric acid-assisted gel,” Materials Letters, vol. 124, pp. 242–244, 2014.

[32] M. Y. Shami, M. S. Awan, and M. Anis-ur-Rehman, “Phasepure synthesis of BiFeO3 nanopowders using diverse precursorvia co-precipitation method,” Journal of Alloys and Com-pounds, vol. 509, no. 41, pp. 10139–10144, 2011.

[33] J.-H. Xu, H. Ke, D.-C. Jia, W. Wang, and Y. Zhou, “Low-temperature synthesis of BiFeO3 nanopowders via a sol–gelmethod,” Journal of Alloys and Compounds, vol. 472, no. 1-2,pp. 473–477, 2009.

[34] S. Li, G. Zhang, H. Zheng, N. Wang, Y. Zheng, and P. Wang,“Microwave-assisted synthesis of BiFeO3 nanoparticles withhigh catalytic performance in microwave-enhanced Fenton-likeprocess,” RSC Advances, vol. 6, no. 85, pp. 82439–82446, 2016.

[35] S. M. Selbach, M.-A. Einarsrud, T. Tybell, and T. Grande,“Synthesis of BiFeO3 by wet chemical methods,” Journal ofthe American Ceramic Society, vol. 90, no. 11, pp. 3430–3434, 2007.

[36] M. Hasan andM. F. Islam, “Enhancement of magnetic proper-ties of nanocrystalline BiFeO3 synthesized by a facile sol-gelauto-combustion process,” International Journal of AdvancedEngineering and Nano Technology, vol. 2, pp. 1–4, 2015.

[37] K. C. Patil, M. S. Hegde, T. Rattan, and S. T. Aruna, Chemistruof Nanocrystalline Oxide Materials. Combustion Synthesis,Properties and Applications, World Scientific Publishing Co.Pte. Ltd, Singapore, 2008.

[38] F. Deganello, G. Marcì, and G. Deganello, “Citrate–nitrateauto-combustion synthesis of perovskite-type nanopowders:a systematic approach,” Journal of the European CeramicSociety, vol. 29, no. 3, pp. 439–450, 2009.

[39] A. Khort, K. Podbolotov, R. Serrano-García, and Y. K. Gun’ko,“One-step solution combustion synthesis of pure Ni nanopow-ders with enhanced coercivity: the fuel effect,” Journal of SolidState Chemistry, vol. 253, pp. 270–276, 2017.

[40] K. B. Podbolotov, A. A. Khort, A. B. Tarasov, G. V. Trusov,S. I. Roslyakov, and A. S. Mukasyan, “Solution combustionsynthesis of copper nanopowders: the fuel effect,” Combus-tion Science and Technology, vol. 189, no. 11, pp. 1878–1890, 2017.

[41] A. Khort, K. Podbolotov, R. Serrano-García, and Y. Gun’ko,“One-step solution combustion synthesis of cobalt nanopow-der in air atmosphere: the fuel effect,” Inorganic Chemistry,vol. 57, no. 3, pp. 1464–1473, 2018.

[42] A. I. Iorgu, F. Maxim, C. Matei et al., “Fast synthesis ofrare-earth (Pr3+, Sm3+, Eu3+ and Gd3+) doped bismuth ferritepowders with enhanced magnetic properties,” Journal of Alloysand Compounds, vol. 629, pp. 62–68, 2015.

[43] B. Stojadinović, Z. Dohčević-Mitrović, N. Paunović et al.,“Comparative study of structural and electrical properties ofPr and Ce doped BiFeO3 ceramics synthesized by auto-combustion method,” Journal of Alloys and Compounds,vol. 657, pp. 866–872, 2016.

[44] P. Trivedi, S. Katba, S. Jethva et al., “Modifications in the elec-tronic structure of rare-earth doped BiFeO3 multiferroic,”Solid State Communications, vol. 222, pp. 5–8, 2015.

[45] C. Beekman, A. A. Reijnders, Y. S. Oh, S. W. Cheong, andK. S. Burch, “Raman study of the phonon symmetries inBiFeO3single crystals,” Physical Review B, vol. 86, no. 2, 2012.

[46] W. Hu, Y. Chen, H. Yuan et al., “Structure, magnetic, andferroelectric properties of Bi1-xGdxFeO3 nanoparticles,” TheJournal of Physical Chemistry C, vol. 115, no. 18, pp. 8869–8875, 2011.

[47] V. R. Reddy, D. Kothari, A. Gupta, and S. M. Gupta, “Study ofweak ferromagnetism in polycrystalline multiferroic Eu dopedbismuth ferrite,” Applied Physics Letters, vol. 94, no. 8, article082505, 2009.

[48] Y. Yao,W. Liu, Y. Chan, C. Leung, C. Mak, and B. Ploss, “Stud-ies of Rare-Earth-Doped BiFeO3 Ceramics,” InternationalJournal of Applied Ceramic Technology, vol. 8, no. 5,pp. 1246–1253, 2011.

10 Journal of Nanomaterials

[49] J. Rout and R. N. P. Choudhary, “Structural transformationand multiferroic properties of Ba–Mn co-doped BiFeO3,”Physics Letters A, vol. 380, no. 1-2, pp. 288–292, 2016.

[50] G. S. Arya, R. K. Sharma, and N. S. Negi, “Enhanced magneticproperties of Sm and Mn co-doped BiFeO3 nanoparticlesat room temperature,” Materials Letters, vol. 93, pp. 341–344, 2013.

[51] A. P. Blessington Selvadurai, V. Pazhanivelu, andR.Murugaraj,“Structural, magnetic, optical and electrical properties of Basubstituted BiFeO3,” Journal of Superconductivity and NovelMagnetism, vol. 27, no. 3, pp. 839–844, 2014.

[52] V. Annapu Reddy, N. P. Pathak, and R. Nath, “Particle sizedependent magnetic properties and phase transitions in multi-ferroic BiFeO3 nano-particles,” Journal of Alloys and Com-pounds, vol. 543, pp. 206–212, 2012.

[53] D. Varshney, A. Kumar, and K. Verma, “Effect of A site and Bsite doping on structural, thermal, and dielectric properties ofBiFeO3 ceramics,” Journal of Alloys and Compounds, vol. 509,no. 33, pp. 8421–8426, 2011.

[54] M. Hasan, M. A. Basith, M. A. Zubair et al., “Saturationmagnetization and band gap tuning in BiFeO3 nanoparticlesvia co-substitution of Gd and Mn,” Journal of Alloys andCompounds, vol. 687, pp. 701–706, 2016.

[55] G. Catalan and J. F. Scott, “Physics and applications ofbismuth ferrite,” Advanced Materials, vol. 21, no. 24,pp. 2463–2485, 2009.

[56] J. Mao, L. Cao, Z. Xiong et al., “Experimental and first princi-ples investigation of Bi1-xCexFeO3: structure, electronic andoptical properties,” Journal of Alloys and Compounds,vol. 721, pp. 638–645, 2017.

[57] B. Bhushan, A. Basumallick, S. K. Bandopadhyay, N. Y.Vasanthacharya, and D. Das, “Effect of alkaline earth metaldoping on thermal, optical, magnetic and dielectric propertiesof BiFeO3nanoparticles,” Journal of Physics D: Applied Physics,vol. 42, no. 6, article 065004, 2009.

[58] S. Irfan, L. Li, A. S. Saleemi, and C.-W. Nan, “Enhancedphotocatalytic activity of La3+ and Se4+ co-doped bismuthferrite nanostructures,” Journal of Materials Chemistry A,vol. 5, no. 22, pp. 11143–11151, 2017.

[59] S. P. Pattnaik, A. Behera, S. Martha, R. Acharya, and K. Parida,“Synthesis, photoelectrochemical properties and solar light-induced photocatalytic activity of bismuth ferrite nanoparti-cles,” Journal of Nanoparticle Research, vol. 20, no. 1, 2018.

[60] A. D. Mani and I. Soibam, “Low temperature synthesis andmanifestation of the structural, dielectric, magnetic and opticalproperties of Bi(Gd)FeO3 nanoparticles,” Nano-Structures &Nano-Objects, vol. 13, pp. 59–66, 2018.

[61] P. Singh, A. Roy, A. Garg, and R. Prasad, “Effect of isovalentnon-magnetic Fe-site doping on the electronic structure andspontaneous polarization of BiFeO3,” Journal of Applied Phys-ics, vol. 117, no. 18, article 184104, 2015.

[62] A. D. Mani and I. Soibam, “Comparative studies of the dielec-tric properties of (1−x)BiFeO3-xNi0.8Zn0.2Fe2O4 (x=0.0, 0.2,0.5, 0.8, 1.0) multiferroic nanocomposite with their singlephase BiFeO3 and Ni0.8Zn0.2Fe2O4,” Physica B: CondensedMatter, vol. 507, pp. 21–26, 2017.

[63] A. Wypych, I. Bobowska, M. Tracz et al., “Dielectric propertiesand characterisation of titanium dioxide obtained by differentchemistry methods,” Journal of Nanomaterials, vol. 2014,Article ID 124814, 9 pages, 2014.

11Journal of Nanomaterials

CorrosionInternational Journal of

Hindawiwww.hindawi.com Volume 2018

Advances in

Materials Science and EngineeringHindawiwww.hindawi.com Volume 2018

Hindawiwww.hindawi.com Volume 2018

Journal of

Chemistry

Analytical ChemistryInternational Journal of

Hindawiwww.hindawi.com Volume 2018

Scienti�caHindawiwww.hindawi.com Volume 2018

Polymer ScienceInternational Journal of

Hindawiwww.hindawi.com Volume 2018

Hindawiwww.hindawi.com Volume 2018

Advances in Condensed Matter Physics

Hindawiwww.hindawi.com Volume 2018

International Journal of

BiomaterialsHindawiwww.hindawi.com

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of

Hindawiwww.hindawi.com Volume 2018

NanotechnologyHindawiwww.hindawi.com Volume 2018

Journal of

Hindawiwww.hindawi.com Volume 2018

High Energy PhysicsAdvances in

Hindawi Publishing Corporation http://www.hindawi.com Volume 2013Hindawiwww.hindawi.com

The Scientific World Journal

Volume 2018

TribologyAdvances in

Hindawiwww.hindawi.com Volume 2018

Hindawiwww.hindawi.com Volume 2018

ChemistryAdvances in

Hindawiwww.hindawi.com Volume 2018

Advances inPhysical Chemistry

Hindawiwww.hindawi.com Volume 2018

BioMed Research InternationalMaterials

Journal of

Hindawiwww.hindawi.com Volume 2018

Na

nom

ate

ria

ls

Hindawiwww.hindawi.com Volume 2018

Journal ofNanomaterials

Submit your manuscripts atwww.hindawi.com