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Enhancement of dielectric, ferromagnetic and electrochemical properties of BiFeO3 nanostructured films through rare earth metal doping
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Enhancement of dielectric, ferromagnetic and electrochemical properties of BiFeO3 nanostructured films through rare earth metal doping R. Anlin Goldaa,∗, A. Marikanib, E. John Alexc a
Department of Electronics and Communication Engineering, JACSI College of Engineering, Nazareth, Tamil Nadu, India Department of Physics, Mepco Schlenk Engineering College, Sivakasi, Tamil Nadu, India c Department of Electronics and Communication Engineering, CMR Institute of Technology, Hyderabad, Telangana, India b
A R T I C LE I N FO
A B S T R A C T
Keywords: Sol-gel Thin film Perovskite Dielectric Electrochemical
In this present work first assessment of enhanced electrochemical properties of Bismuth Ferrite (BiFeO3)thin films through Samarium(Sm) doping are delivered. Apart from this enhancement of structural, dielectric and magnetic properties with increasing samarium concentration is discussed. The pure phase BiFeO3 films and Smdoped BiFeO3(Bi1-xSmxFeO3 where x = 0.05 & x = 0.1) films were synthesized using 2methoxy aided sol-gel process and were deposited on platinum substrates through spin coating technique. X-ray diffraction confirmed the formation of pure phase BiFeO3 with Rhombohedral (R3c) structure. Morphological characterization through SEM presented the formation of nanostructures and its structural transformation through doping variant. AFM confirmed the smoothness of the film with a maximum grain size of 172.72 nm for the measured films. The elemental analysis and elemental purity was confirmed through EDAX. Mechanistic aspects of the prepared films were analyzed through Thermogravimetric, Differential Thermal Analysis and Fourier Transform Infrared spectroscopy. The variation of dielectric constant with frequency was measured until 1 MHz and remains almost constant due to the independent nature of polarization with frequency. The magnetic coercivity of the film improved from 77.7G to 240G with samarium doping. The Bi0.9Sm0.1FeO3 films deposited on platinum substrates enhanced the specific capacity to about 184Fg-1 along with its retention capability enabling it to be used as electrode material for supercapacitors.
1. Introduction Multiferroics is a branch of science that relates the dependence between spins and charge transfer of electrons. Multiferroic materials concurrently posses a ferroic order parameters explicitly like ferroelectricity, ferromagnetism, ferroelasticity and ferrotoroidicity [1]. Among the pervoskite multiferroic material, bismuth ferrite [BF] has been the most researched material as they posses room temperature ferroelectricity and ferrimagnetism [2] with high transition temperature to paraelectric and paramagnetic nature. Various forms of bismuth ferrite as bulk ceramics [3], single crystals nanopowders [4], thin films [5] and thick films [6] have been investigated widely, although thin epitaxially grown films are explored for their application in miniaturized electronic devices. The thin films are deposited on various substrates through Electrodeposition [7–9], Radio Frequency sputtering [10], spray pyrolysis [11], Pulsed Laser Deposition [12] Atomic layer Deposition [13], Magnetron Sputtering [14], Molecular beam epitaxy [15]. Nevertheless, Chemical deposition method like solgel processed
∗
spin coating assist in developing cost effective, pure phase, high homogeneity, nanostructured and low temperature processed thin films for various applications. Most recently hydrogen sensing characteristics of the BiFeO3thin films has been reported where the sensing properties were improved by calcium doping [16]. Wan et al. [17] have reported that the optical properties of BiFeO3thin films for electronic and optical devices. Biswas et al. [18] have demonstrated the photovoltaic property of lanthanum doped BiFeO3 films. Mariam et al. [19] have reported the photocatalytic property of gadolinium and tin doped BiFeO3 thin films through increased photo generated electrons. In all these applications it is noted that the physical properties of the BiFeO3 films can be enhanced through doping by increasing the oxygen vacancy, strain state, and band gap. Moreover, the high leakage current density and weak ferromagnetism can be improved by doping with rare earth metals. Under this condition, several studies relating to functional properties improvement of BiFeO3 thin films through lanthanide doping like Pr, Yb, La, Nd, Sm, Gd, etc,. have been reported. Certain studies have been made on the electrochemical properties of BiFeO3. Lignesh et al.
Corresponding author. E-mail address: [email protected] (R. Anlin Golda).
https://doi.org/10.1016/j.ceramint.2019.09.175 Received 31 July 2019; Received in revised form 17 September 2019; Accepted 18 September 2019 0272-8842/ © 2019 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: R. Anlin Golda, A. Marikani and E. John Alex, Ceramics International, https://doi.org/10.1016/j.ceramint.2019.09.175
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Fig. 1. (a) DTA curve of the Bi1-xSmxFeO3 films (b) TG curve of the Bi1-xSmxFeO3 films.
Initially bismuth nitrate and iron nitrate were dissolved separately in 2-methoxyethanol [C3H8O2] through constant stirring. After the dissolution of the nitrates the two solutions was mixed together to which 2 drops of acetic acid [CH3COOH] was added to catalyze the reaction. The solution was heated to 40 °C and was kept under constant stirring at 400 rpm for 5 h. During gel formation, few drops of diethanol amine [C4H11NO2] were added to the solution as a stabilizer and for adjusting the viscosity of the solution. The prepared gel was removed from heat and allowed to cool at room temperature. The Si/SiO2/TiO2/ Pt substrates were washed with acetone and sonicated in distilled water. The Si/SiO2/TiO2/Pt substrate was chosen as the Pt thin layer helps to improve the electrical properties [25] by modifying the grain size of polarization domains [26]. The prepared gel was spin coated on Pt substrate at 3000 rpm for 45Sec. After deposition of each layer, the substrate was kept in a hot plate at 250 °C for 2 min. After deposition of five to six layers through consecutive heating process, the thin films were annealed at 550 °C for 6 h. The as-deposited gel was subjected to Thermogravimetric and Differential Thermal Analysis [TG/DTA, PerkinElmer - TGA 4000], The films were subjected to crystallographic measurements with Bruker D8 Advance X-ray Diffractometer (XRD) operating at a radiation wavelength (λ) of 1.5406Aͦ in the 2theta range 10–90° with the step size 0.02°s-1. The Fourier Transformation Infrared Spectroscopy (FTIR – Bruker Alpha E model, Germany) was carried out to confirm the functional groups present in the film. The morphology of the film was observed using a Scanning Electron Microscope (SEM - Carl zeiss supra55) and the elemental confirmation was made using EDAX. The topography of the surface was studied using Atomic Force Microscope (AFM - Park System-XE 70). The dielectric measurements of the film were carried out in the frequency range 42 Hz to1 MHz by applying 1 V at room temperature using Hioki LCZ meter. The magnetic properties were studied using Vibrating Sample Magnetometer (VSM – Lakeshore 7404). The Electrochemical properties were studied using an electrochemical workstation (chi660C new, CH instruments, USA).
[20] have studied the use of BiFeO3 nanoparticles as anode material for batteries and have reported specific capacitance value of about 675 mA h/g. Nanoflakes BiFeO3 as electrode material for super capacitor has been carried out by vijaykumar et al. [21] and a specific capacitance of 101.63 F/g was reported. Cyclic voltammetry performance of TiO2 was improved by Ce and Sm doping from 4.53 mCcm2 to 15.2 mCcm2 by Niu et al. [22]. To the best of our knowledge, however, there is no research in the literature on the Electrochemical properties Smdoped BiFeO3. Moreover, samarium has been proved to improve the magnetic and ferroelectric property of the BF films. The BiFeO3 posses zero remanent magnetization due to the antiferromagnetic spin structure. To improve the magneto-electric coupling of BF, the Bi3+ site can be substituted with an magnetically active cation. Zhang et al. [23] have established the improvement in remanent magnetization to 0.007emu/g in BF ceramics through samarium doping synthesized using solid state reaction. Dielectric constant of BF films remains low due to the defects caused by the volatilization of bismuth and oxygen vacancies. For use in memory application, the need for high dielectric constant can be made possible through doping. Yu et al. [24] have shown the improvement in dielectric constant of the BF ceramics through the removal of defects by introducing Sm dopant. In the present work, pure phase BiFeO3 [BF], Bi0.95Sm 0.05FeO3 and Bi0.9Sm 0.1FeO3 were synthesized using sol-gel technique and spin coated on platinum substrates at 3000 rpm. The films were subjected to annealing at 550 °C for 6 h. The effect of samarium doping in BF films for structural, dielectric, vibrational, magnetic and electrochemical properties were examined and discussed. 2. Materials and methods Pure phase bismuth ferrite (BiFeO3), Sm-doped bismuth ferrite films at different concentration Bi1-xSmxFeO3 where x = 0.05 & x = 0.1 (Bi0.95Sm 0.05FeO3, Bi0.9Sm 0.1FeO3) were prepared through methoxy aided sol-gel technique and the films were deposited in commercial Si/ SiO2/TiO2/Pt substrates using spin coating technique. The starting materials for the synthesis of Sm-doped bismuth ferrite films were bismuth nitrate pentahydrate (Bi(NO3)3·5H2O), samarium hexahydrate (Sm(NO3)·6H2O) and iron nitrate (Fe(NO3)3·9H2O. The chemicals were purchased from sigma Aldrich and was taken in the ratio (Bi:Sm:Fe) 1:0:1 for BiFeO3, 0.95:0.05:1 for Bi0.95Sm 0.05FeO3 and 0.90:0.1:1 for Bi0.9Sm 0.1FeO3 with additional 10% weight of bismuth nitrate to compensate the losses during the sol-gel process.
3. Results and discussion 3.1. Thermal studies using TG/DTA The Differential Thermal Analysis and Thermogravimetric analysis of bismuth ferrite and samarium doped bismuth ferrite films were carried out in order to determine the sintering temperature for 2
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Fig. 2. (a)XRD pattern of the Bi1-xSmxFeO3 films (b) Enlarged view of the peak around 32°
Fig. 3. W–H plot of Bi1-xSmxFeO3 films (a)x = 0.05 (b)x = 0.1. Table 1 Variation between the unit cell parameters of the Bi1-xSmxFeO3 films. Samples Bi1-xSmxFeO3
Crystalline Size(nm) D
BiFeO3 Bi0.95Sm 0.05FeO3 Bi0.9Sm 0.1FeO3
69 ± 0.05 44 ± 0.05 45 ± 0.05
Inter-Planar spacing(Aͦ )(dhkl)
2.786 2.779 2.776
Lattice parameters a = b(Aͦ )
c(Aͦ )
5.566 5.561 5.554
13.860 13.874 13.793
crystalline and pure phases of the film. It can be inferred from Fig. 1 (a& b) that all the compounds exhibit exothermic peaks and weight loss phases under three temperature stages. The peaks in the range 120 °C to 300 °C with 5%, 5% and 2% weight loss of BiFeO3, Bi0.95Sm 0.05FeO3
Volume V (Aͦ )3
Lattice Strain(η)
Dislocation density(10-3) δ
371.81 371.17 366.8
0.002 0.008 0.007
0.2 0.6 0.7
and Bi0.9Sm 0.1FeO3 were due to the hydration of the water molecules and nitrates trapped in the surface of the nanostructures. While the sharp exothermic peaks observed around 300 °C, 400 °C and 500 °C arise due to the oxidation of Bi 3+ ions and Fe 3+ ions with a weight loss 3
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Fig. 4. SEM Micrographs of Bi1-xSmxFeO3 films(a) x = 0 (b) x = 0.05 (c) x = 0.1 and cross sectional images of images Bi1-xSmxFeO3 films(d) x = 0 (e) x = 0.05 (f) x = 0.1.
samarium is increased from 5 to 10%, the impurity peaks get disappeared proving the incorporation of trivalent Sm ions in the BF crystal structure. The undoped BF films have two well defined characteristic diffraction peaks at 31.78, 32.08 corresponding to (104) (110) and as samarium is doped both the peak merges and tend to form a single peak as shown in Fig. 2(b). However the splitted peak exist till 10% doping of samarium preserving the rhombohedral structure and investigation on previous literatures report shows a possible transition to orthorhombic structure as doping is increased further [31]. Doping of rare earth metals to certain levels with unchanged structural transition implies that it helps in evading the oxygen vacancies or other oxidational states of Fe3+ which favors the formation of impurity phases [32]. It can be observed that the doped films shows slight shifting of the characteristics peaks towards higher diffraction angle which is due to the comparatively smaller ionic radius of Sm3+(0.96 Aͦ ) ions than Bi3+ (1.03Aͦ )ions [33]. Further, Scherrer's formula (Eq. (1)) was used for the estimation of crystallite size of BFSm0.05, BFSm0.1 films and found to be 44 and 46 nm.
of 35%, 40%, 5% in BiFeO3, Bi0.95Sm 0.05FeO3 and Bi0.9Sm 0.1FeO3. The maximum weight loss is attributed by the pyrolysis of the organic residues [27]. The final evaporation stage around 450 to 600 °C presents the decomposition of the oxides Bi2O3 and Fe2O3 with a total weight loss of 65%, 40% and 5% for BF, BFSm0.05 and BFSm0.1 After 500 °C the weight loss remains almost constant indicating the formation of crystalline phases and the absence of organic residues. Consequently, from the observed thermal behavior the sintering temperature was set at 600 °C for 6 h s. 3.2. X-ray diffraction studies The X-ray diffraction pattern of the pure phase BiFeO3, Bi0.95Sm and Bi0.9Sm 0.1FeO3 films are shown in Fig. 2(a). The films coated on the Si/SiO2/TiO2/Pt substrates exhibited diffraction peaks (111) and (100) corresponding to Pt and Si. The pure phase BF films revealed diffraction peaks (012) (104)(110)(113)(024)(116)(125)(220) showing a distorted pervoskite based rhombohedral structure with R3c space group that corresponds with the JCPDS file: 86–1518. In addition, the presence of sharp and distinct peaks indicates polycrystalline nature of the film. It can be noted that Fe rich phases of BF namely Bi2Fe4O9 appear at the diffraction peaks (121) (211) (002) (231) and matches with the JCPDS file: 72–1832. The presence of orthorhombic structured impurities in BF normally occurs due to the kinetics of compound formation and has been reported by Godara et al. and Puli et al. [28,29]. Although increasing the samarium content lubricates the formation of single phase BF as it gets well doped in the A site of the crystal structure [30]. From the XRD data it was observed that as the doping of 0.05FeO3
D=
kλ β cosθ
(1)
Where k = 0.9 D-Crystallite size, β- Full Width Half Maximum of the peak in radian, θ – diffraction angle, λ – wavelength of X-Ray. The dislocation density (δ) of the BiFeO3, Bi0.95Sm 0.05FeO3 and Bi0.9Sm 0.1FeO3 films were calculated using Eqn. (2). It was examined that dislocation density increases with samarium doping due to the varied ionic radius of Bi3+ and Sm3+ ions. 4
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Fig. 5. EDAX analysis of Bi1-xSmxFeO3 films(a) x = 0 (b) x = 0.05 (c) x = 0.1.
δ=
1 D2
The surface diffusion of atoms takes place to lower the surface energy during the process of sintering and determines the direction of crystallographic growth [38]. The cross sectional view shows a distinct integration between the substrate and the film. The thickness of the films varies depending on the viscosity of the gel and number of layers deposited. With the addition of 5% (Bi0.95Sm 0.05FeO3) doping concentration of samarium, the nanoflakes structure grows to form an agglomerated flower like structure due to the surface diffusion of the atoms. On increase of samarium doping concentration to 10% (Bi0.9Sm 0.1FeO3) causes the nanoflakes to be grouped into nanosheet like structures due to increased surface migration of atoms and nucleation density. The reason behind the formation of nanostructures can be explained through Wulff's theorem, Which states that formation of structures of different shapes happens through the reduction in free energy. The structures get into a stable form when they match with the equilibrium shape of the crystal. The flake like structure formed in the present work matches with the polyhedron wulffs construction or equilllirium shape of the crystal [39]. As a result smooth nanoflakes structures are formed with no hills and valleys for BF and a surface reconstruction happens to form facets when samarium is doped to reduce the free energy. Moreover it has been proved by fu et al. that the perovskite form nanoplate like structure through nucleation and growth [40]. The compositional investigation of the Bi1-xSmxFeO3 films was carried out using Energy Dispersive X-ray Spectroscopy (EDAX) to confirm the presence of samarium dopant at various concentrations(5 and 10%) in the elemental level. The characteristic peaks due to energy emission of Sm, Bi, Fe and O ions can be observed in Fig. 5 and the relative ratio between Sm and Bi atoms matches with the prepared stoichiometry concentration. The absence of other impurity peaks confirms the uniform distribution of the dopant throughout the film. The distinguished variations in the surface nanostructures alter the
(2)
The microstrain imposed on the lattice structure due to the doping of Sm3+ ions was studied using Williamson-Hall(W–H) plot shown in Fig. 3(a&b) The W–H relationship of the lorentzian peak was derived by plotting a graph between sinθ and βcosθ. The crystalline size and strain can be calculated from the intercept and slope of the linear fit to the data [34,35]. The strain is calcuated from the relation given in Eqn. (3)
βcosθ =
Kλ + 4ηsinθ D
(3)
β is the integral breadth of reflection, D is the crystallite size, λ is the wavelength of Xray radiation, K is the dimensionless factor and η is the strain. In the present study the W–H plot shows a positive slope indicating tensile strain [36]. The tensile strain for 5% doping of samarium is 0.008 and reduces to 0.007 for 10% doping of samarium. The high lattice strain is due to the presence of the defects in the structure like oxygen vacancies [37]. The calculated lattice parameters are shown in Table 1. 3.3. Morphological analysis The surface morphology of nanoflakes structured BiFeO3, Bi0.95Sm and Bi0.9Sm 0.1FeO3 films along with its cross sectional images are shown in Fig. 4(a–f). The surface of BF exhibit dense growth of the flake like structures with few holes between them confirming crystallized nature of the films. The longitudinal dimension of the flakes was found to be around 500 nm while the thickness was found to be around 80 nm. BF is formed due to the diffusion of atoms between Bi2O3 and Fe2O3. 0.05FeO3
Bi2O3 + Fe2O3 → 2BiFeO3
(4) 5
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Fig. 6. AFM images of Bi1-xSmxFeO3 films (a)x = 0 (b)x = 0.05 (c)x = 0.1. Table 2 Surface roughness parameters of the of Bi1-xSmxFeO3 films. Roughness Parameters
BiFeO3
Bi0.95Sm
Rpv(nm) Rq(nm) Ra(nm) Rku
168.547 34.068 28.638 2.556
172.727 31.623 22.739 4.56
0.05FeO3
Bi0.9Sm
0.1FeO3
113.509 14.903 11.074 6.141
transmittance spectra, dielectric, magnetic and electrochemical properties of the material which are discussed below. 3.4. Topographical analysis The surface topography of the deposited Bi1-xSmxFeO3 films observed using AFM is shown in Fig. 6(a–c). The nanostructures observed using SEM could be confirmed through the topographical view. The flake like structure of bismuth ferrite films appears to be formed at an average height (Rz) of 124 nm and decreases as 105 nm, 70 nm with samarium doping. The surface roughness of the films were calculated through the root mean square value of roughness (Rq), root mean square of peak-valley depth (Rpv), and root mean square value of surface height deviation (Ra). It can be observed from Table 2 that the value of Rq improves with increase in samarium doping concentration due to the surface diffusion of the grains [41]. Meanwhile, the increases in Kurtosis value (Rku) indicates the transformation of flake like structure into sheets that was earlier identified using SEM image. The topographical transformation also confirms that the annealing
Fig. 7. FTIR Spectra of Bi1-xSmxFeO3 films (x = 0,x = 0.05,x = 0.1).
temperature was sufficient to drive the films into crystalline phase. 3.5. Fourier transform spectroscopy The finger print region from the Fourier Transform Infrared 6
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Fig. 8. Plot of (a). Variation of dielectric constant with frequency (b) Variation of dielectric loss with frequency of Bi1-xSmxFeO3 films (x = 0,x = 0.05,x = 0.1).
the defects like oxygen vacancy and leaky boundaries.
Spectroscopy is analyzed for determining the functional groups of Bi1xSmxFeO3 films and is shown in Fig. 7. The strong transmittance peaks observed at 551 cm-1 can be attributed to the bending and stretching vibrations of O–Fe–O, Fe–O bond indicating the formation of FeO6 Octahedral structure. The metal-oxygen bond confirms the formation of perovskite structure. The spectra at 590 cm-1 is basically due to the phase vibration of oxygen atoms normal to (111) plane of the rhombohedral structure BF [42]. The peak at 693 cm-1 is ascribed to the bending vibrations of Bi2O3 present in the octahedral structure [43]. The shift in the peaks of BF with samarium doping confirms the substitution of Sm3+ ions in the place of Bi3+ ions. The peak at 811 cm-1 confirms the crystalline nature of the films [44]. The peaks from 1209 to 1526 cm-1 arises due to the presence of nitrates.
3.7. Magnetic studies The variation of magnetization with respect to the applied field at room temperature is shown in Fig. 9(a–c). It was observed that the BF films exhibit a week ferromagnetism with a nonzero remanent magnetization(Mr) of 0.0007 emu/cm3 and the magnetization increases to 0.0019 emu/cm3 for x = 0.05 doped samarium and 0.0057 for x = 0.1 doped samarium. In contrast to the antiferromagnetic nature, the BF films show a week ferromagnetic behavior due to the destruction of the spiral magnetic ordering in the film [50] However Fe rich phases and size effect also contribute to the ferromagnetism. Moreover increase in magnetization with doping concentration can be due to the (i) Destruction of the modulated cycloid spin structure of BF film [51] (ii) The uncompensated surface spins that arise due to breakage in the spin cycloid as the particle size gets reduced below 62 nm [52]. Dopants can be seen to play a major role in altering the magnetization because of the varied ionic radii of Sm3+ and Bi3+ ion or due the magneto electric coupling. Although, samarium doping increases the magnetization its not of an appreciable amount since the magnetization arise from the increase in cell volume and other lattice parameters. On increasing dopant concentration above 10%, phase transition occurs which results in complete destruction of the spin cycloid and increased magnetization value [53]. The magnetic coercivity (Hc) for the undoped film with increasing samarium concentration was observed to be 77.7G, 161.5G and 240G. The increase in coercivity can also be related to the structural and morphological changes of the film [54]. The reduction in film roughness leads to the repression of the spiral spin arrangement resulting in the homogenous spin structure and increased ferromagnetism.
3.6. Dielectric studies The variation of dielectric constant and dielectric loss with frequency at room temperature is shown in Fig. 8 (a&b). It was observed that the dielectric constant of BF films at all doping concentration of samarium decreases with frequency and remains almost constant in the higher frequency range(> 200 kHz). Increasing the concentration of samarium to 5% increases the dielectric constant of the BF films. The increase in dielectric constant with doping is due to the doping of smaller ionic radii Sm3+ ions in higher ionic radii Bi3+ ions which create a large vibration space for the dipole moment thereby increasing the dielectric constant [45]. Moreover, it can be seen that the dielectric constant does not increases monotonously with dopant concentration. The high dielectric constant of the BFSm0.05 films is due to the presence of defects like oxygen vacancies and metal in vacancies. The decrease in dielectric constant with 10% samarium doping (Bi0.9Sm 0.1FeO3) film is due to the fewer defects in the lattice as the dopant occupies the vacant positions [46]. The high dielectric constant at lower frequencies can be attributed by the interfacial polarization which causes the accumulation of dipoles along the grain boundary [47]. As the frequency increases, the direction of electron motion changes rapidly disturbing the movement of electrons within the grains and reduces the interfacial polarization, which in turn reduces the dielectric constant. Dielectric loss of the films remains close to each other indicating similar quality. Dielectric loss appears to be high at low frequencies due to space charge polarization losses and decreases with increasing frequency as the movement of charge carriers is hindered [48,49]. Increase in dielectric loss with doping concentration is due to
3.8. Electrochemical studies The cyclic voltammetry (CV) analysis of BiFeO3, Bi0.95Sm 0.05FeO3 and Bi0.9Sm 0.1FeO3 films material for potential application in super capacitors was carried out. Super capacitive application also depends on electrolyte nature and therefore 0.5 M of Na2SO4 was chosen to match the PH of the thin films. The three prepared thin film electrodes were subjected to different voltage scan rates of 25 mV s-1, 50 mV s-1, 75 mV s-1 and 100 mV s-1 in the potential window of -1 t0+1.5 mV. Fig. 10(a–c) show distinct redox peaks due to electron transfer between 7
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Fig. 9. Magnetization hysteresis loop of Bi1-xSmxFeO3 films (a)x = 0 (b)x = 0.05(c) x = 0.1).
turn increases the current. The GCD curve of the films shown in Fig. 11 was analyzed further to study the performance of the electrode for supercapacitors. It can be observed that the curves show symmetric charge and discharges cycles which is the ideal property of the Pseudo capacitive electrochemical cells. The specific capacitance can be calculated from the GCD curve using eqn. (5)
various oxidation states of the metal ions Bi, Sm and Fe along with the electrolyte. In the CV analysis of pure phase BF(x = 0) electrodes the oxidation/reduction peaks of Bi2+ and Fe2+ appears around 0.25 V and 0.1 V. Whereas 5%(x = 0.05) doping of samarium in the BF films introduces one more redox peak around 0.5 V. It can also been seen that increase in samarium doping increases the peak intensity and therefore the peak current. This proves the pseudo capacitive nature of the electrodes. It can also be observed from the graphs that the cycle area and peak current of BF films remains to be low and continues to increase with the doping concentration. The Randles-Sevick plot shown in Fig. 10(d) follows a linear pattern indicating the dependence of peak current on the scan rate, which also confirms the diffusion based redox reaction on the surface of the electrode. The increase in peak current with scan rate is due to the migration of neutral molecules in the electrolyte and their diffusion into the electrode. Whereas at lower potential, formation of substantial diffusion layer in the electrode prevents the adsorption of free moving ions into the solution. At higher potential, the electrical flux inhibits the growth of diffusion layer and creates a concentration gradient in the vicinity of the electrode which in
Cs =
iΔt mΔV
(5)
Where i-Charge/Discharge current, Δt-Time for Charging/Discharging, m-mass of the electrode, ΔV-Potential window. The observations from the GCD profiles show that the charging time and the storage capacity for the Bi0.9Sm 0.1FeO3 electrode is significantly higher than the pure BF electrodes and the results are consistent with the CV profile. The specific capacitance of the pure BF films was 40Fg-1 for a current density of 10 A g-1 and increases to 64Fg-1 for Bi0.95Sm 0.05FeO3 and 184Fg-1 for Bi0.9Sm 0.1FeO3. The specific capacitance of BF film is considerably similar to values reported in the literatures [20,21,50,51]. The formation of nanosheets in the Bi0.9Sm 8
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Fig 10. Cyclic Voltammetry plot of Bi1-xSmxFeO3 films (a)x = 0 (b)x = 0.05 (c)x = 0.1 (d) Randles-Sevick plot.
films might have increased the transfer of charges by ballistics means through the narrow axis of the sheets rather than the diffusion mechanism observed in BF films. The retention capacitance was calculated for 100 cycles and BF showed 60% retention while Bi0.9Sm 0.1FeO3 exhibited 90% retention as shown in Fig. 11(b). It was clearly observed from these electrochemical studies that the Sm-doped BF films as electrode material for supercapacitors exhibits a capacitance higher than that of pure BF films. Further, the Electrochemical Impedance Spectroscopy (EIS) was carried out to study the electrical conductivity due to the movement of ions between the electrode and electrolyte. The observed Nyquist plots and Bode plots are shown in Fig. 12(a–c). Here the Nyquist plot between the real and imaginary impedance for all the films starts up a semicircular path at low frequencies and ends up at higher frequencies following the same charge transfer principle. The impedance spectra of the pure BF and doped films were plotted and the parameters were fitted through the Randles modified equivalent circuit using the EIS spectrum analyzer software. Fig. 12(d) represents the fitted impedance spectra of BF films with the inset figure showing the equivalent circuit which was found to be the same for the doped films. The resistive
parameter R1 corresponds to the resistance offered by the ions in the electrolyte, the electrode, and the resistance between electrode and collector. The parameter R2 corresponds to the charge transfer resistance between the electrolyte and the electrode and can be calculated from the diameter of the semicircle. It can be observed from the Nyquist plot that the BF films have high resistance value of 13.5 Ω and are reduced significantly to 3.3 Ω through 10% doping of samarium thereby increasing the ion transfer ability. The resistive and capacitive parameters of the Randles modified equivalent circuit of the films are given in Table 3. The common phase element CPE1 corresponds to the electrical double layer formed in the electrode-electrolyte interface. The linear nature of the plot at low frequency is due to the additional diffusive element CPE2 present in the circuit. The diffusive element may be due to the number of diffusion species present in the electrolyte, random diffusion or concentration variation of the electrolyte. All the perturbations are reversible at low frequencies and apart from diffusion ion migration, ion replacement and intercalation have also been reported elsewhere [55–57].
0.1FeO3
9
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Fig. 11. (a) GCD curve of the Bi1-xSmxFeO3 films (x = 0,x = 0.05,x = 0.1) (b) Stability analysis.
Fig. 12. EIS of Bi1-xSmxFeO3 films showing (a) Nyquist plot; Bode plots showing (b) Magnitude (c) Phase angle Vs Frequency (d) Equivalent circuit for the fitted data of BF film.
4. Conclusion
substrates. The structural and morphological studies showed formation of nanoflakes and its transformation to sheet like structures with a grain size around 45 nm. The surface roughness of the films and nanostructures were confirmed through AFM. The improved dielectric
To summarize, BiFeO3, Bi0.95Sm 0.05FeO3 and Bi0.9Sm 0.1FeO3 films were prepared through sol-gel process and spin coated on platinum 10
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Table 3 Electrical parameters of the Randles modified equivalent circuit of the films.
BiFeO3, Bi0.95Sm 0.05FeO3 Bi0.9Sm 0.1FeO3
R1 Ω
R2 M Ω
CPE1 μF
CPE2 μF
427.98 413.59 315.39
12.57 10.8 3.32
5.389 6.53 12.025
4.0422 3.294 2.14
[17] H. Wang, F. Khatkhatay, J. Jian, J. Huang, M. Fan, H. Wang, Strain tuning of ferroelectric and optical properties of rhombohedral-like BiFeO3 thin films on SrRuO3buffered substrates, Mater. Res. Bull. 110 (2019) 120–125. [18] D. Li, D. Zheng, C. Jin, W. Zheng, H. Bai, High-performance photovoltaic readable ferroelectric nonvolatile memory based on La-doped BiFeO3 films, ACS Appl. Mater. Interfaces 10 (23) (2018) 19836–19843. [19] M. Kiani, A.B. Kiani, S.A. Khan, S. ur Rehmana, Q.U. Khan, I. Mahmood, L. Zhu, Facile synthesis of Gd and Sn co-doped BiFeO3 supported on nitrogen doped graphene for enhanced photocatalytic activity, J. Phys. Chem. Solids 130 (2019) 222–229. [20] L. Durai, B. Moorthy, C.I. Thomas, D.K. Kim, K.K. Bharathi, Electrochemical properties of BiFeO3 nanoparticles: anode material for sodium-ion battery application, Mater. Sci. Semicond. Process. 68 (2017) 165–171. [21] V.V. Jadhav, M.K. Zate, S. Liu, M. Naushad, R.S. Mane, K.N. Hui, S.H. Han, Mixedphase bismuth ferrite nanoflake electrodes for supercapacitor application, Appl. Nanosci. 6 (4) (2016) 511–519. [22] W. Niu, X. Bi, G. Wang, X. Sun, TiO2 gel thin film doped Ce and Sm preparation and cyclic voltammetry characteristics, Int. J. Electrochem. Sci 8 (2013) 11943–11950. [23] F. Zhang, X. Zeng, D. Bi, K. Guo, Y. Yao, S. Lu, Dielectric, ferroelectric, and magnetic properties of Sm-doped BiFeO3 ceramics prepared by a modified solid-statereaction method, Materials 11 (11) (2018) 2208. [24] C. Yu, G. Viola, D. Zhang, K. Zhou, V. Koval, A. Mahajan, H. Yan, Phase evolution and electrical behaviour of samarium-substituted bismuth ferrite ceramics, J. Eur. Ceram. Soc. 38 (4) (2018) 1374–1380. [25] J. Zhu, D. Xiao, W. Zhang, J. Zhu, Z. Qian, Epitaxial or high-oriented platinum thin films grown on various substrates by the RF magnetron sputtering technique, Physica Status Solidi. A, Appl. Res. 139 (1) (1993) K17–K20. [26] P.M. Deleuze, A. Mahmoud, B. Domenichini, C. Dupont, Theoretical investigation of the platinum substrate influence on BaTiO 3 thin film polarisation, Phys. Chem. Chem. Phys. 21 (8) (2019) 4367–4374. [27] M. Sakar, S. Balakumar, P. Saravanan, S.N. Jaisankar, Annealing temperature mediated physical properties of bismuth ferrite (BiFeO3) nanostructures synthesized by a novel wet chemical method, Mater. Res. Bull. 48 (8) (2013) 2878–2885. [28] P. Godara, A. Agarwal, N. Ahlawat, S. Sanghi, Crystal structure refinement, dielectric and magnetic properties of Sm modified BiFeO3 multiferroic, J. Mol. Struct. 1097 (2015) 207–213. [29] V.S. Puli, D.K. Pradhan, R.K. Katiyar, I. Coondoo, N. Panwar, P. Misra, R.S. Katiyar, Photovoltaic effect in transition metal modified polycrystalline BiFeO3 thin films, J. Phys. D Appl. Phys. 47 (7) (2014) 075502. [30] C.S. Tu, C.S. Chen, P.Y. Chen, H.H. Wei, V.H. Schmidt, C.Y. Lin, J.M. Lee, Enhanced photovoltaic effects in A-site samarium doped BiFeO3 ceramics: the roles of domain structure and electronic state, J. Eur. Ceram. Soc. 36 (5) (2016) 1149–1157. [31] W. Sun, J.F. Li, Q. Yu, L.Q. Cheng, Phase transition and piezoelectricity of sol–gelprocessed Sm-doped BiFeO 3 thin films on Pt (111)/Ti/SiO 2/Si substrates, J. Mater. Chem. C 3 (9) (2015) 2115–2122. [32] X. Xu, T. Guoqiang, R. Huijun, X. Ao, Structural, electric and multiferroic properties of Sm-doped BiFeO3 thin films prepared by the sol–gelprocess, Ceram. Int. 39 (6) (2013) 6223–6228. [33] C. Anthonyraj, M. Muneeswaran, S.G. Raj, N.V. Giridharan, V. Sivakumar, G. Senguttuvan, Effect of samarium doping on the structural, optical and magnetic properties of sol–gel processed BiFeO 3 thin films, J. Mater. Sci. Mater. Electron. 26 (1) (2015) 49–58. [34] P. Kumar, P. Chand, Structural, electric transport response and electro-strain-polarization effect in La and Ni modified bismuth ferrite nanostructures, J. Alloy. Comp. 748 (2018) 504–514. [35] P. Veluswamy, S. Sathiyamoorthy, P. Santhoshkumar, G. Karunakaran, C.W. Lee, D. Kuznetsov, H. Ikeda, Sono-synthesis approach of reduced graphene oxide for ammonia vapour detection at room temperature, Ultrason. Sonochem. 48 (2018) 555–566. [36] A. Thakur, P. Thakur, J.H. Hsu, Smart magnetodielectric nano-materials for the very high frequency applications, J. Alloy. Comp. 509 (17) (2011) 5315–5319. [37] S.K. Gore, R.S. Mane, M. Naushad, S.S. Jadhav, M.K. Zate, Z.A. Alothman, B.K. Hui, Influence of Bi 3+-doping on the magnetic and Mössbauer properties of spinel cobalt ferrite, Dalton Trans. 44 (14) (2015) 6384–6390. [38] B. Andrzejewski, K. Chybczynska, B. Hilczer, M. Blaszyk, T. Lucinski, M. Matczak, L. Kepinski, Controlled growth of bismuth ferrite multiferroic flowers, 1402.1336, (2014). [39] C. Herring, Some theorems on the free energies of crystal surfaces, Phys. Rev. 82 (1) (1951) 87. [40] Y. Fu, T. Wu, J. Wang, J. Zhai, M.J. Shearer, Y. Zhao, S. Jin, Stabilization of the metastable lead iodide perovskite phase via surface functionalization, Nano Lett. 17 (7) (2017) 4405–4414. [41] K. Ravaliya, A. Ravalia, D.D. Pandya, P.S. Solanki, N.A. Shah, Strain and morphology control over electrical behavior of pulsed laser deposited BiFeO3 films, Thin Solid Films 645 (2018) 436–443. [42] C.A. Kumar, G.G. Rao, K. Samatha, S. Bharadwaj, M.P. Dasari, Observation on magnetic variation for low concentration of bismuth and samarium doped Ni–Co ferrites, Karbala Int. J. Modern Sci. 4 (1) (2018) 143–150. [43] H. Wu, P. Xue, Y. Lu, X. Zhu, Microstructural, optical and magnetic characterizations of BiFeO3 multiferroic nanoparticles synthesized via a sol-gel process, J. Alloy. Comp. 731 (2018) 471–477. [44] R. Pandey, C. Panda, P. Kumar, M. Kar, Phase diagram of Sm and Mn co-doped bismuth ferrite based on crystal structure and magnetic properties, J. Sol. Gel Sci. Technol. 85 (1) (2018) 166–177. [45] W. Li, O. Auciello, R.N. Premnath, B. Kabius, Giant dielectric constant dominated by Maxwell–Wagner relaxation in Al 2 O 3/TiO 2 nanolaminates synthesized by atomic
property, magnetic property and electrochemical properties were studied. It can be seen that the dielectric constant of BFfilms is varied between 149 and 182 with samarium doping. In the mean while the remanet magnetization was improved from 0.0007 emu/cm3 to 0.0057 emu/cm3. Through electrochemical studies the BF and the doped films where studied for electrode material in super capacitors, the specific capacitance of the films increased from 40Fg-1 to 184Fg-1. Through all these measurements it can be confirmed that the BF films which have wide range of functional properties can be further enhanced that through samarium doping without any structural transition for use in microelectronic devices. Acknowledgement The Authors are thankful to the Principal and Management of Mepco Schlenk Engineering College for the experimental facilities and support rendered for the research. References [1] W. Eerenstein, N.D. Mathur, J.F. Scott, Multiferroic and magnetoelectric materials, Nature 442 (7104) (2006) 759. [2] J. Wu, Z. Fan, D. Xiao, J. Zhu, J. Wang, Multiferroic bismuth ferrite-based materials for multifunctional applications: ceramic bulks, thin films and nanostructures, Prog. Mater. Sci. 84 (2016) 335–402. [3] J. Wei, Y. Liu, X. Bai, C. Li, Y. Liu, Z. Xu, B. Dkhil, Crystal structure, leakage conduction mechanism evolution and enhanced multiferroic properties in Y-doped BiFeO3 ceramics, Ceram. Int. 42 (12) (2016) 13395–13403. [4] A. Manzoor, A.M. Afzal, N. Amin, M.I. Arshad, M. Usman, M.N. Rasool, M.F. Khan, Investigation of dielectric and optical properties of structurally modified bismuth ferrite nanomaterials, Ceram. Int. 42 (9) (2016) 11447–11452. [5] D. Tiwari, D.J. Fermin, T.K. Chaudhuri, A. Ray, Solution processed bismuth ferrite thin films for all-oxide solar photovoltaics, J. Phys. Chem. C 119 (11) (2015) 5872–5877. [6] T. Rojac, E. Khomyakova, J. Walker, H. Ursic, A. Bencan, BiFeO3 ceramics and thick films: processing issues and electromechanical properties, Magnetic, Ferroelectric, and Multiferroic Metal Oxides, Elsevier, 2018, pp. 515–525. [7] D. Bilican, E. Menéndez, J. Zhang, P. Solsona, J. Fornell, E. Pellicer, J. Sort, Ferromagnetic-like behaviour in bismuth ferrite films prepared by electrodeposition and subsequent heat treatment, RSC Adv. 7 (51) (2017) 32133–32138. [8] L. Saravanan, M.M. Raja, D. Prabhu, V. Pandiyarasan, H. Ikeda, H.A. Therese, Perpendicular magnetic anisotropy in Mo/Co2FeAl0. 5Si0. 5/MgO/Mo multilayers with optimal Mo buffer layer thickness, J. Magn. Magn. Mater. 454 (2018) 267–273. [9] L. Saravanan, D. Prabhu, V. Pandiyarasan, H. Ikeda, H.A. Therese, Impact of MgO thickness on the perpendicular magnetic anisotropy of Mo/Co2FeAl/MgO/Mo multilayers with improved annealing stability, Mater. Res. Bull. 107 (2018) 118–124. [10] X. Deng, J. Huang, Y. Sun, K. Liu, R. Gao, W. Cai, C. Fu, Effect of processing parameters on the structural, electrical and magnetic properties of BFO thin film synthesized via RF magnetron sputtering, J. Alloy. Comp. 684 (2016) 510–515. [11] P.V. Mane, N.B. Shinde, I.M. Mulla, R.R. Koli, A.R. Shelke, M.M. Karanjkar, N.G. Deshpande, Bismuth ferrite thin film as an efficient electrode for photocatalytic degradation of Methylene blue dye, Mater. Res. Express 6 (2) (2018) 026426. [12] Z.Z. Jiang, Z. Guan, N. Yang, P.H. Xiang, R.J. Qi, R. Huang, C.G. Duan, Epitaxial growth of BiFeO3 films on SrRuO3/SrTiO3, Mater. Char. 131 (2017) 217–223. [13] P. Jalkanen, V. Tuboltsev, B. Marchand, A. Savin, M. Puttaswamy, M. Vehkamäki, J. Räisänen, Magnetic properties of polycrystalline bismuth ferrite thin films grown by atomic layer deposition, J. Phys. Chem. Lett. 5 (24) (2014) 4319–4323. [14] A. Iljinas, V. Stankus, Structural and ferroelectric properties of bismuth ferrite thin films deposited by direct current reactive magnetron sputtering, Thin Solid Films 601 (2016) 106–110. [15] A.B. Mei, Y. Tang, J. Schubert, D. Jena, H. Xing, D.C. Ralph, D.G. Schlom, Selfassembly and properties of domain walls in BiFeO3 layers grown via molecularbeam epitaxy, Apl. Mater. 7 (7) (2019) 071101. [16] A. Bala, S.B. Majumder, M. Dewan, A.R. Chaudhuri, Hydrogen sensing characteristics of perovskite based calcium doped BiFeO3 thin films, Int. J. Hydrogen Energy 44 (33) (2019) 18648–18656.
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layer deposition, Appl. Phys. Lett. 96 (16) (2010) 162907. [46] X. Xu, T. Guoqiang, R. Huijun, X. Ao, Structural, electric and multiferroic properties of Sm-doped BiFeO3 thin films prepared by the sol–gelprocess, Ceram. Int. 39 (6) (2013) 6223–6228. [47] K. Ulutas, D. Deger, S. Yakut, Thickness dependence of the dielectric properties of thermally evaporated Sb2Te3 thin films, Journal of Physics: Conference Series, vol 417, IOP Publishing, 2013, p. 012040 No. 1. [48] H. Ji, W. Ren, L. Wang, P. Shi, X. Chen, X. Wu, K.K. Shung, Structure and electrical properties of Na 0.5 Bi 0.5 TiO 3 ferroelectric thick films derived from a polymer modified sol-gel method, IEEE Trans. Ultrason. Ferroelectr. Freq. Control 58 (10) (2011) 2042–2049. [49] D.A.I. Haiyang, C.H.E.N. Zhenping, L.I. Tao, L.I. Yong, Microstructure and properties of Sm-substituted BiFeO3 ceramics, J. Rare Earths 30 (11) (2012) 1123–1128. [50] G.S. Arya, R.K. Sharma, N.S. Negi, Enhanced magnetic properties of Sm and Mn codoped BiFeO3 nanoparticles at room temperature, Mater. Lett. 93 (2013) 341–344. [51] N. Dutta, S.K. Bandyopadhyay, S. Rana, P. Sen, A.K. Himanshu, Remarkably high value of capacitance in BiFeO3 Nanorod, 1309.5690, (2013). [52] A. Sarkar, A.K. Singh, D. Sarkar, G.G. Khan, K. Mandal, Three-dimensional
[53]
[54] [55]
[56]
[57]
12
nanoarchitecture of BiFeO3 anchored TiO2 nanotube arrays for electrochemical energy storage and solar energy conversion, ACS Sustain. Chem. Eng. 3 (9) (2015) 2254–2263. P. Godara, A. Agarwal, N. Ahlawat, S. Sanghi, Crystal structure refinement, dielectric and magnetic properties of Sm modified BiFeO3 multiferroic, J. Mol. Struct. 1097 (2015) 207–213. D.A.I. Haiyang, C.H.E.N. Zhenping, L.I. Tao, L.I. Yong, Microstructure and properties of Sm-substituted BiFeO3 ceramics, J. Rare Earths 30 (11) (2012) 1123–1128. Z. Xiao, Y. Yuan, Y. Shao, Q. Wang, Q. Dong, C. Bi, J. Huang, Giant switchable photovoltaic effect in organometal trihalide perovskite devices, Nat. Mater. 14 (2) (2015) 193. T.Y. Yang, G. Gregori, N. Pellet, M. Grätzel, J. Maier, The significance of ion conduction in a hybrid organic–inorganic lead‐iodide‐based perovskite photosensitizer, Angew. Chem. Int. Ed. 54 (27) (2015) 7905–7910. C.H. Hendon, R.X. Yang, L.A. Burton, A. Walsh, Assessment of polyanion (BF 4− and PF 6−) substitutions in hybrid halide perovskites, J. Mater. Chem. 3 (17) (2015) 9067–9070.
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Enhancement of dielectric, ferromagnetic and electrochemical properties of BiFeO3 nanostructured films through rare earth metal doping R. Anlin Goldaa,∗, A. Marikanib, E. John Alexc a
Department of Electronics and Communication Engineering, JACSI College of Engineering, Nazareth, Tamil Nadu, India Department of Physics, Mepco Schlenk Engineering College, Sivakasi, Tamil Nadu, India c Department of Electronics and Communication Engineering, CMR Institute of Technology, Hyderabad, Telangana, India b
A R T I C LE I N FO
A B S T R A C T
Keywords: Sol-gel Thin film Perovskite Dielectric Electrochemical
In this present work first assessment of enhanced electrochemical properties of Bismuth Ferrite (BiFeO3)thin films through Samarium(Sm) doping are delivered. Apart from this enhancement of structural, dielectric and magnetic properties with increasing samarium concentration is discussed. The pure phase BiFeO3 films and Smdoped BiFeO3(Bi1-xSmxFeO3 where x = 0.05 & x = 0.1) films were synthesized using 2methoxy aided sol-gel process and were deposited on platinum substrates through spin coating technique. X-ray diffraction confirmed the formation of pure phase BiFeO3 with Rhombohedral (R3c) structure. Morphological characterization through SEM presented the formation of nanostructures and its structural transformation through doping variant. AFM confirmed the smoothness of the film with a maximum grain size of 172.72 nm for the measured films. The elemental analysis and elemental purity was confirmed through EDAX. Mechanistic aspects of the prepared films were analyzed through Thermogravimetric, Differential Thermal Analysis and Fourier Transform Infrared spectroscopy. The variation of dielectric constant with frequency was measured until 1 MHz and remains almost constant due to the independent nature of polarization with frequency. The magnetic coercivity of the film improved from 77.7G to 240G with samarium doping. The Bi0.9Sm0.1FeO3 films deposited on platinum substrates enhanced the specific capacity to about 184Fg-1 along with its retention capability enabling it to be used as electrode material for supercapacitors.
1. Introduction Multiferroics is a branch of science that relates the dependence between spins and charge transfer of electrons. Multiferroic materials concurrently posses a ferroic order parameters explicitly like ferroelectricity, ferromagnetism, ferroelasticity and ferrotoroidicity [1]. Among the pervoskite multiferroic material, bismuth ferrite [BF] has been the most researched material as they posses room temperature ferroelectricity and ferrimagnetism [2] with high transition temperature to paraelectric and paramagnetic nature. Various forms of bismuth ferrite as bulk ceramics [3], single crystals nanopowders [4], thin films [5] and thick films [6] have been investigated widely, although thin epitaxially grown films are explored for their application in miniaturized electronic devices. The thin films are deposited on various substrates through Electrodeposition [7–9], Radio Frequency sputtering [10], spray pyrolysis [11], Pulsed Laser Deposition [12] Atomic layer Deposition [13], Magnetron Sputtering [14], Molecular beam epitaxy [15]. Nevertheless, Chemical deposition method like solgel processed
∗
spin coating assist in developing cost effective, pure phase, high homogeneity, nanostructured and low temperature processed thin films for various applications. Most recently hydrogen sensing characteristics of the BiFeO3thin films has been reported where the sensing properties were improved by calcium doping [16]. Wan et al. [17] have reported that the optical properties of BiFeO3thin films for electronic and optical devices. Biswas et al. [18] have demonstrated the photovoltaic property of lanthanum doped BiFeO3 films. Mariam et al. [19] have reported the photocatalytic property of gadolinium and tin doped BiFeO3 thin films through increased photo generated electrons. In all these applications it is noted that the physical properties of the BiFeO3 films can be enhanced through doping by increasing the oxygen vacancy, strain state, and band gap. Moreover, the high leakage current density and weak ferromagnetism can be improved by doping with rare earth metals. Under this condition, several studies relating to functional properties improvement of BiFeO3 thin films through lanthanide doping like Pr, Yb, La, Nd, Sm, Gd, etc,. have been reported. Certain studies have been made on the electrochemical properties of BiFeO3. Lignesh et al.
Corresponding author. E-mail address: [email protected] (R. Anlin Golda).
https://doi.org/10.1016/j.ceramint.2019.09.175 Received 31 July 2019; Received in revised form 17 September 2019; Accepted 18 September 2019 0272-8842/ © 2019 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: R. Anlin Golda, A. Marikani and E. John Alex, Ceramics International, https://doi.org/10.1016/j.ceramint.2019.09.175
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Fig. 1. (a) DTA curve of the Bi1-xSmxFeO3 films (b) TG curve of the Bi1-xSmxFeO3 films.
Initially bismuth nitrate and iron nitrate were dissolved separately in 2-methoxyethanol [C3H8O2] through constant stirring. After the dissolution of the nitrates the two solutions was mixed together to which 2 drops of acetic acid [CH3COOH] was added to catalyze the reaction. The solution was heated to 40 °C and was kept under constant stirring at 400 rpm for 5 h. During gel formation, few drops of diethanol amine [C4H11NO2] were added to the solution as a stabilizer and for adjusting the viscosity of the solution. The prepared gel was removed from heat and allowed to cool at room temperature. The Si/SiO2/TiO2/ Pt substrates were washed with acetone and sonicated in distilled water. The Si/SiO2/TiO2/Pt substrate was chosen as the Pt thin layer helps to improve the electrical properties [25] by modifying the grain size of polarization domains [26]. The prepared gel was spin coated on Pt substrate at 3000 rpm for 45Sec. After deposition of each layer, the substrate was kept in a hot plate at 250 °C for 2 min. After deposition of five to six layers through consecutive heating process, the thin films were annealed at 550 °C for 6 h. The as-deposited gel was subjected to Thermogravimetric and Differential Thermal Analysis [TG/DTA, PerkinElmer - TGA 4000], The films were subjected to crystallographic measurements with Bruker D8 Advance X-ray Diffractometer (XRD) operating at a radiation wavelength (λ) of 1.5406Aͦ in the 2theta range 10–90° with the step size 0.02°s-1. The Fourier Transformation Infrared Spectroscopy (FTIR – Bruker Alpha E model, Germany) was carried out to confirm the functional groups present in the film. The morphology of the film was observed using a Scanning Electron Microscope (SEM - Carl zeiss supra55) and the elemental confirmation was made using EDAX. The topography of the surface was studied using Atomic Force Microscope (AFM - Park System-XE 70). The dielectric measurements of the film were carried out in the frequency range 42 Hz to1 MHz by applying 1 V at room temperature using Hioki LCZ meter. The magnetic properties were studied using Vibrating Sample Magnetometer (VSM – Lakeshore 7404). The Electrochemical properties were studied using an electrochemical workstation (chi660C new, CH instruments, USA).
[20] have studied the use of BiFeO3 nanoparticles as anode material for batteries and have reported specific capacitance value of about 675 mA h/g. Nanoflakes BiFeO3 as electrode material for super capacitor has been carried out by vijaykumar et al. [21] and a specific capacitance of 101.63 F/g was reported. Cyclic voltammetry performance of TiO2 was improved by Ce and Sm doping from 4.53 mCcm2 to 15.2 mCcm2 by Niu et al. [22]. To the best of our knowledge, however, there is no research in the literature on the Electrochemical properties Smdoped BiFeO3. Moreover, samarium has been proved to improve the magnetic and ferroelectric property of the BF films. The BiFeO3 posses zero remanent magnetization due to the antiferromagnetic spin structure. To improve the magneto-electric coupling of BF, the Bi3+ site can be substituted with an magnetically active cation. Zhang et al. [23] have established the improvement in remanent magnetization to 0.007emu/g in BF ceramics through samarium doping synthesized using solid state reaction. Dielectric constant of BF films remains low due to the defects caused by the volatilization of bismuth and oxygen vacancies. For use in memory application, the need for high dielectric constant can be made possible through doping. Yu et al. [24] have shown the improvement in dielectric constant of the BF ceramics through the removal of defects by introducing Sm dopant. In the present work, pure phase BiFeO3 [BF], Bi0.95Sm 0.05FeO3 and Bi0.9Sm 0.1FeO3 were synthesized using sol-gel technique and spin coated on platinum substrates at 3000 rpm. The films were subjected to annealing at 550 °C for 6 h. The effect of samarium doping in BF films for structural, dielectric, vibrational, magnetic and electrochemical properties were examined and discussed. 2. Materials and methods Pure phase bismuth ferrite (BiFeO3), Sm-doped bismuth ferrite films at different concentration Bi1-xSmxFeO3 where x = 0.05 & x = 0.1 (Bi0.95Sm 0.05FeO3, Bi0.9Sm 0.1FeO3) were prepared through methoxy aided sol-gel technique and the films were deposited in commercial Si/ SiO2/TiO2/Pt substrates using spin coating technique. The starting materials for the synthesis of Sm-doped bismuth ferrite films were bismuth nitrate pentahydrate (Bi(NO3)3·5H2O), samarium hexahydrate (Sm(NO3)·6H2O) and iron nitrate (Fe(NO3)3·9H2O. The chemicals were purchased from sigma Aldrich and was taken in the ratio (Bi:Sm:Fe) 1:0:1 for BiFeO3, 0.95:0.05:1 for Bi0.95Sm 0.05FeO3 and 0.90:0.1:1 for Bi0.9Sm 0.1FeO3 with additional 10% weight of bismuth nitrate to compensate the losses during the sol-gel process.
3. Results and discussion 3.1. Thermal studies using TG/DTA The Differential Thermal Analysis and Thermogravimetric analysis of bismuth ferrite and samarium doped bismuth ferrite films were carried out in order to determine the sintering temperature for 2
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Fig. 2. (a)XRD pattern of the Bi1-xSmxFeO3 films (b) Enlarged view of the peak around 32°
Fig. 3. W–H plot of Bi1-xSmxFeO3 films (a)x = 0.05 (b)x = 0.1. Table 1 Variation between the unit cell parameters of the Bi1-xSmxFeO3 films. Samples Bi1-xSmxFeO3
Crystalline Size(nm) D
BiFeO3 Bi0.95Sm 0.05FeO3 Bi0.9Sm 0.1FeO3
69 ± 0.05 44 ± 0.05 45 ± 0.05
Inter-Planar spacing(Aͦ )(dhkl)
2.786 2.779 2.776
Lattice parameters a = b(Aͦ )
c(Aͦ )
5.566 5.561 5.554
13.860 13.874 13.793
crystalline and pure phases of the film. It can be inferred from Fig. 1 (a& b) that all the compounds exhibit exothermic peaks and weight loss phases under three temperature stages. The peaks in the range 120 °C to 300 °C with 5%, 5% and 2% weight loss of BiFeO3, Bi0.95Sm 0.05FeO3
Volume V (Aͦ )3
Lattice Strain(η)
Dislocation density(10-3) δ
371.81 371.17 366.8
0.002 0.008 0.007
0.2 0.6 0.7
and Bi0.9Sm 0.1FeO3 were due to the hydration of the water molecules and nitrates trapped in the surface of the nanostructures. While the sharp exothermic peaks observed around 300 °C, 400 °C and 500 °C arise due to the oxidation of Bi 3+ ions and Fe 3+ ions with a weight loss 3
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Fig. 4. SEM Micrographs of Bi1-xSmxFeO3 films(a) x = 0 (b) x = 0.05 (c) x = 0.1 and cross sectional images of images Bi1-xSmxFeO3 films(d) x = 0 (e) x = 0.05 (f) x = 0.1.
samarium is increased from 5 to 10%, the impurity peaks get disappeared proving the incorporation of trivalent Sm ions in the BF crystal structure. The undoped BF films have two well defined characteristic diffraction peaks at 31.78, 32.08 corresponding to (104) (110) and as samarium is doped both the peak merges and tend to form a single peak as shown in Fig. 2(b). However the splitted peak exist till 10% doping of samarium preserving the rhombohedral structure and investigation on previous literatures report shows a possible transition to orthorhombic structure as doping is increased further [31]. Doping of rare earth metals to certain levels with unchanged structural transition implies that it helps in evading the oxygen vacancies or other oxidational states of Fe3+ which favors the formation of impurity phases [32]. It can be observed that the doped films shows slight shifting of the characteristics peaks towards higher diffraction angle which is due to the comparatively smaller ionic radius of Sm3+(0.96 Aͦ ) ions than Bi3+ (1.03Aͦ )ions [33]. Further, Scherrer's formula (Eq. (1)) was used for the estimation of crystallite size of BFSm0.05, BFSm0.1 films and found to be 44 and 46 nm.
of 35%, 40%, 5% in BiFeO3, Bi0.95Sm 0.05FeO3 and Bi0.9Sm 0.1FeO3. The maximum weight loss is attributed by the pyrolysis of the organic residues [27]. The final evaporation stage around 450 to 600 °C presents the decomposition of the oxides Bi2O3 and Fe2O3 with a total weight loss of 65%, 40% and 5% for BF, BFSm0.05 and BFSm0.1 After 500 °C the weight loss remains almost constant indicating the formation of crystalline phases and the absence of organic residues. Consequently, from the observed thermal behavior the sintering temperature was set at 600 °C for 6 h s. 3.2. X-ray diffraction studies The X-ray diffraction pattern of the pure phase BiFeO3, Bi0.95Sm and Bi0.9Sm 0.1FeO3 films are shown in Fig. 2(a). The films coated on the Si/SiO2/TiO2/Pt substrates exhibited diffraction peaks (111) and (100) corresponding to Pt and Si. The pure phase BF films revealed diffraction peaks (012) (104)(110)(113)(024)(116)(125)(220) showing a distorted pervoskite based rhombohedral structure with R3c space group that corresponds with the JCPDS file: 86–1518. In addition, the presence of sharp and distinct peaks indicates polycrystalline nature of the film. It can be noted that Fe rich phases of BF namely Bi2Fe4O9 appear at the diffraction peaks (121) (211) (002) (231) and matches with the JCPDS file: 72–1832. The presence of orthorhombic structured impurities in BF normally occurs due to the kinetics of compound formation and has been reported by Godara et al. and Puli et al. [28,29]. Although increasing the samarium content lubricates the formation of single phase BF as it gets well doped in the A site of the crystal structure [30]. From the XRD data it was observed that as the doping of 0.05FeO3
D=
kλ β cosθ
(1)
Where k = 0.9 D-Crystallite size, β- Full Width Half Maximum of the peak in radian, θ – diffraction angle, λ – wavelength of X-Ray. The dislocation density (δ) of the BiFeO3, Bi0.95Sm 0.05FeO3 and Bi0.9Sm 0.1FeO3 films were calculated using Eqn. (2). It was examined that dislocation density increases with samarium doping due to the varied ionic radius of Bi3+ and Sm3+ ions. 4
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Fig. 5. EDAX analysis of Bi1-xSmxFeO3 films(a) x = 0 (b) x = 0.05 (c) x = 0.1.
δ=
1 D2
The surface diffusion of atoms takes place to lower the surface energy during the process of sintering and determines the direction of crystallographic growth [38]. The cross sectional view shows a distinct integration between the substrate and the film. The thickness of the films varies depending on the viscosity of the gel and number of layers deposited. With the addition of 5% (Bi0.95Sm 0.05FeO3) doping concentration of samarium, the nanoflakes structure grows to form an agglomerated flower like structure due to the surface diffusion of the atoms. On increase of samarium doping concentration to 10% (Bi0.9Sm 0.1FeO3) causes the nanoflakes to be grouped into nanosheet like structures due to increased surface migration of atoms and nucleation density. The reason behind the formation of nanostructures can be explained through Wulff's theorem, Which states that formation of structures of different shapes happens through the reduction in free energy. The structures get into a stable form when they match with the equilibrium shape of the crystal. The flake like structure formed in the present work matches with the polyhedron wulffs construction or equilllirium shape of the crystal [39]. As a result smooth nanoflakes structures are formed with no hills and valleys for BF and a surface reconstruction happens to form facets when samarium is doped to reduce the free energy. Moreover it has been proved by fu et al. that the perovskite form nanoplate like structure through nucleation and growth [40]. The compositional investigation of the Bi1-xSmxFeO3 films was carried out using Energy Dispersive X-ray Spectroscopy (EDAX) to confirm the presence of samarium dopant at various concentrations(5 and 10%) in the elemental level. The characteristic peaks due to energy emission of Sm, Bi, Fe and O ions can be observed in Fig. 5 and the relative ratio between Sm and Bi atoms matches with the prepared stoichiometry concentration. The absence of other impurity peaks confirms the uniform distribution of the dopant throughout the film. The distinguished variations in the surface nanostructures alter the
(2)
The microstrain imposed on the lattice structure due to the doping of Sm3+ ions was studied using Williamson-Hall(W–H) plot shown in Fig. 3(a&b) The W–H relationship of the lorentzian peak was derived by plotting a graph between sinθ and βcosθ. The crystalline size and strain can be calculated from the intercept and slope of the linear fit to the data [34,35]. The strain is calcuated from the relation given in Eqn. (3)
βcosθ =
Kλ + 4ηsinθ D
(3)
β is the integral breadth of reflection, D is the crystallite size, λ is the wavelength of Xray radiation, K is the dimensionless factor and η is the strain. In the present study the W–H plot shows a positive slope indicating tensile strain [36]. The tensile strain for 5% doping of samarium is 0.008 and reduces to 0.007 for 10% doping of samarium. The high lattice strain is due to the presence of the defects in the structure like oxygen vacancies [37]. The calculated lattice parameters are shown in Table 1. 3.3. Morphological analysis The surface morphology of nanoflakes structured BiFeO3, Bi0.95Sm and Bi0.9Sm 0.1FeO3 films along with its cross sectional images are shown in Fig. 4(a–f). The surface of BF exhibit dense growth of the flake like structures with few holes between them confirming crystallized nature of the films. The longitudinal dimension of the flakes was found to be around 500 nm while the thickness was found to be around 80 nm. BF is formed due to the diffusion of atoms between Bi2O3 and Fe2O3. 0.05FeO3
Bi2O3 + Fe2O3 → 2BiFeO3
(4) 5
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Fig. 6. AFM images of Bi1-xSmxFeO3 films (a)x = 0 (b)x = 0.05 (c)x = 0.1. Table 2 Surface roughness parameters of the of Bi1-xSmxFeO3 films. Roughness Parameters
BiFeO3
Bi0.95Sm
Rpv(nm) Rq(nm) Ra(nm) Rku
168.547 34.068 28.638 2.556
172.727 31.623 22.739 4.56
0.05FeO3
Bi0.9Sm
0.1FeO3
113.509 14.903 11.074 6.141
transmittance spectra, dielectric, magnetic and electrochemical properties of the material which are discussed below. 3.4. Topographical analysis The surface topography of the deposited Bi1-xSmxFeO3 films observed using AFM is shown in Fig. 6(a–c). The nanostructures observed using SEM could be confirmed through the topographical view. The flake like structure of bismuth ferrite films appears to be formed at an average height (Rz) of 124 nm and decreases as 105 nm, 70 nm with samarium doping. The surface roughness of the films were calculated through the root mean square value of roughness (Rq), root mean square of peak-valley depth (Rpv), and root mean square value of surface height deviation (Ra). It can be observed from Table 2 that the value of Rq improves with increase in samarium doping concentration due to the surface diffusion of the grains [41]. Meanwhile, the increases in Kurtosis value (Rku) indicates the transformation of flake like structure into sheets that was earlier identified using SEM image. The topographical transformation also confirms that the annealing
Fig. 7. FTIR Spectra of Bi1-xSmxFeO3 films (x = 0,x = 0.05,x = 0.1).
temperature was sufficient to drive the films into crystalline phase. 3.5. Fourier transform spectroscopy The finger print region from the Fourier Transform Infrared 6
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Fig. 8. Plot of (a). Variation of dielectric constant with frequency (b) Variation of dielectric loss with frequency of Bi1-xSmxFeO3 films (x = 0,x = 0.05,x = 0.1).
the defects like oxygen vacancy and leaky boundaries.
Spectroscopy is analyzed for determining the functional groups of Bi1xSmxFeO3 films and is shown in Fig. 7. The strong transmittance peaks observed at 551 cm-1 can be attributed to the bending and stretching vibrations of O–Fe–O, Fe–O bond indicating the formation of FeO6 Octahedral structure. The metal-oxygen bond confirms the formation of perovskite structure. The spectra at 590 cm-1 is basically due to the phase vibration of oxygen atoms normal to (111) plane of the rhombohedral structure BF [42]. The peak at 693 cm-1 is ascribed to the bending vibrations of Bi2O3 present in the octahedral structure [43]. The shift in the peaks of BF with samarium doping confirms the substitution of Sm3+ ions in the place of Bi3+ ions. The peak at 811 cm-1 confirms the crystalline nature of the films [44]. The peaks from 1209 to 1526 cm-1 arises due to the presence of nitrates.
3.7. Magnetic studies The variation of magnetization with respect to the applied field at room temperature is shown in Fig. 9(a–c). It was observed that the BF films exhibit a week ferromagnetism with a nonzero remanent magnetization(Mr) of 0.0007 emu/cm3 and the magnetization increases to 0.0019 emu/cm3 for x = 0.05 doped samarium and 0.0057 for x = 0.1 doped samarium. In contrast to the antiferromagnetic nature, the BF films show a week ferromagnetic behavior due to the destruction of the spiral magnetic ordering in the film [50] However Fe rich phases and size effect also contribute to the ferromagnetism. Moreover increase in magnetization with doping concentration can be due to the (i) Destruction of the modulated cycloid spin structure of BF film [51] (ii) The uncompensated surface spins that arise due to breakage in the spin cycloid as the particle size gets reduced below 62 nm [52]. Dopants can be seen to play a major role in altering the magnetization because of the varied ionic radii of Sm3+ and Bi3+ ion or due the magneto electric coupling. Although, samarium doping increases the magnetization its not of an appreciable amount since the magnetization arise from the increase in cell volume and other lattice parameters. On increasing dopant concentration above 10%, phase transition occurs which results in complete destruction of the spin cycloid and increased magnetization value [53]. The magnetic coercivity (Hc) for the undoped film with increasing samarium concentration was observed to be 77.7G, 161.5G and 240G. The increase in coercivity can also be related to the structural and morphological changes of the film [54]. The reduction in film roughness leads to the repression of the spiral spin arrangement resulting in the homogenous spin structure and increased ferromagnetism.
3.6. Dielectric studies The variation of dielectric constant and dielectric loss with frequency at room temperature is shown in Fig. 8 (a&b). It was observed that the dielectric constant of BF films at all doping concentration of samarium decreases with frequency and remains almost constant in the higher frequency range(> 200 kHz). Increasing the concentration of samarium to 5% increases the dielectric constant of the BF films. The increase in dielectric constant with doping is due to the doping of smaller ionic radii Sm3+ ions in higher ionic radii Bi3+ ions which create a large vibration space for the dipole moment thereby increasing the dielectric constant [45]. Moreover, it can be seen that the dielectric constant does not increases monotonously with dopant concentration. The high dielectric constant of the BFSm0.05 films is due to the presence of defects like oxygen vacancies and metal in vacancies. The decrease in dielectric constant with 10% samarium doping (Bi0.9Sm 0.1FeO3) film is due to the fewer defects in the lattice as the dopant occupies the vacant positions [46]. The high dielectric constant at lower frequencies can be attributed by the interfacial polarization which causes the accumulation of dipoles along the grain boundary [47]. As the frequency increases, the direction of electron motion changes rapidly disturbing the movement of electrons within the grains and reduces the interfacial polarization, which in turn reduces the dielectric constant. Dielectric loss of the films remains close to each other indicating similar quality. Dielectric loss appears to be high at low frequencies due to space charge polarization losses and decreases with increasing frequency as the movement of charge carriers is hindered [48,49]. Increase in dielectric loss with doping concentration is due to
3.8. Electrochemical studies The cyclic voltammetry (CV) analysis of BiFeO3, Bi0.95Sm 0.05FeO3 and Bi0.9Sm 0.1FeO3 films material for potential application in super capacitors was carried out. Super capacitive application also depends on electrolyte nature and therefore 0.5 M of Na2SO4 was chosen to match the PH of the thin films. The three prepared thin film electrodes were subjected to different voltage scan rates of 25 mV s-1, 50 mV s-1, 75 mV s-1 and 100 mV s-1 in the potential window of -1 t0+1.5 mV. Fig. 10(a–c) show distinct redox peaks due to electron transfer between 7
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Fig. 9. Magnetization hysteresis loop of Bi1-xSmxFeO3 films (a)x = 0 (b)x = 0.05(c) x = 0.1).
turn increases the current. The GCD curve of the films shown in Fig. 11 was analyzed further to study the performance of the electrode for supercapacitors. It can be observed that the curves show symmetric charge and discharges cycles which is the ideal property of the Pseudo capacitive electrochemical cells. The specific capacitance can be calculated from the GCD curve using eqn. (5)
various oxidation states of the metal ions Bi, Sm and Fe along with the electrolyte. In the CV analysis of pure phase BF(x = 0) electrodes the oxidation/reduction peaks of Bi2+ and Fe2+ appears around 0.25 V and 0.1 V. Whereas 5%(x = 0.05) doping of samarium in the BF films introduces one more redox peak around 0.5 V. It can also been seen that increase in samarium doping increases the peak intensity and therefore the peak current. This proves the pseudo capacitive nature of the electrodes. It can also be observed from the graphs that the cycle area and peak current of BF films remains to be low and continues to increase with the doping concentration. The Randles-Sevick plot shown in Fig. 10(d) follows a linear pattern indicating the dependence of peak current on the scan rate, which also confirms the diffusion based redox reaction on the surface of the electrode. The increase in peak current with scan rate is due to the migration of neutral molecules in the electrolyte and their diffusion into the electrode. Whereas at lower potential, formation of substantial diffusion layer in the electrode prevents the adsorption of free moving ions into the solution. At higher potential, the electrical flux inhibits the growth of diffusion layer and creates a concentration gradient in the vicinity of the electrode which in
Cs =
iΔt mΔV
(5)
Where i-Charge/Discharge current, Δt-Time for Charging/Discharging, m-mass of the electrode, ΔV-Potential window. The observations from the GCD profiles show that the charging time and the storage capacity for the Bi0.9Sm 0.1FeO3 electrode is significantly higher than the pure BF electrodes and the results are consistent with the CV profile. The specific capacitance of the pure BF films was 40Fg-1 for a current density of 10 A g-1 and increases to 64Fg-1 for Bi0.95Sm 0.05FeO3 and 184Fg-1 for Bi0.9Sm 0.1FeO3. The specific capacitance of BF film is considerably similar to values reported in the literatures [20,21,50,51]. The formation of nanosheets in the Bi0.9Sm 8
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Fig 10. Cyclic Voltammetry plot of Bi1-xSmxFeO3 films (a)x = 0 (b)x = 0.05 (c)x = 0.1 (d) Randles-Sevick plot.
films might have increased the transfer of charges by ballistics means through the narrow axis of the sheets rather than the diffusion mechanism observed in BF films. The retention capacitance was calculated for 100 cycles and BF showed 60% retention while Bi0.9Sm 0.1FeO3 exhibited 90% retention as shown in Fig. 11(b). It was clearly observed from these electrochemical studies that the Sm-doped BF films as electrode material for supercapacitors exhibits a capacitance higher than that of pure BF films. Further, the Electrochemical Impedance Spectroscopy (EIS) was carried out to study the electrical conductivity due to the movement of ions between the electrode and electrolyte. The observed Nyquist plots and Bode plots are shown in Fig. 12(a–c). Here the Nyquist plot between the real and imaginary impedance for all the films starts up a semicircular path at low frequencies and ends up at higher frequencies following the same charge transfer principle. The impedance spectra of the pure BF and doped films were plotted and the parameters were fitted through the Randles modified equivalent circuit using the EIS spectrum analyzer software. Fig. 12(d) represents the fitted impedance spectra of BF films with the inset figure showing the equivalent circuit which was found to be the same for the doped films. The resistive
parameter R1 corresponds to the resistance offered by the ions in the electrolyte, the electrode, and the resistance between electrode and collector. The parameter R2 corresponds to the charge transfer resistance between the electrolyte and the electrode and can be calculated from the diameter of the semicircle. It can be observed from the Nyquist plot that the BF films have high resistance value of 13.5 Ω and are reduced significantly to 3.3 Ω through 10% doping of samarium thereby increasing the ion transfer ability. The resistive and capacitive parameters of the Randles modified equivalent circuit of the films are given in Table 3. The common phase element CPE1 corresponds to the electrical double layer formed in the electrode-electrolyte interface. The linear nature of the plot at low frequency is due to the additional diffusive element CPE2 present in the circuit. The diffusive element may be due to the number of diffusion species present in the electrolyte, random diffusion or concentration variation of the electrolyte. All the perturbations are reversible at low frequencies and apart from diffusion ion migration, ion replacement and intercalation have also been reported elsewhere [55–57].
0.1FeO3
9
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Fig. 11. (a) GCD curve of the Bi1-xSmxFeO3 films (x = 0,x = 0.05,x = 0.1) (b) Stability analysis.
Fig. 12. EIS of Bi1-xSmxFeO3 films showing (a) Nyquist plot; Bode plots showing (b) Magnitude (c) Phase angle Vs Frequency (d) Equivalent circuit for the fitted data of BF film.
4. Conclusion
substrates. The structural and morphological studies showed formation of nanoflakes and its transformation to sheet like structures with a grain size around 45 nm. The surface roughness of the films and nanostructures were confirmed through AFM. The improved dielectric
To summarize, BiFeO3, Bi0.95Sm 0.05FeO3 and Bi0.9Sm 0.1FeO3 films were prepared through sol-gel process and spin coated on platinum 10
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Table 3 Electrical parameters of the Randles modified equivalent circuit of the films.
BiFeO3, Bi0.95Sm 0.05FeO3 Bi0.9Sm 0.1FeO3
R1 Ω
R2 M Ω
CPE1 μF
CPE2 μF
427.98 413.59 315.39
12.57 10.8 3.32
5.389 6.53 12.025
4.0422 3.294 2.14
[17] H. Wang, F. Khatkhatay, J. Jian, J. Huang, M. Fan, H. Wang, Strain tuning of ferroelectric and optical properties of rhombohedral-like BiFeO3 thin films on SrRuO3buffered substrates, Mater. Res. Bull. 110 (2019) 120–125. [18] D. Li, D. Zheng, C. Jin, W. Zheng, H. Bai, High-performance photovoltaic readable ferroelectric nonvolatile memory based on La-doped BiFeO3 films, ACS Appl. Mater. Interfaces 10 (23) (2018) 19836–19843. [19] M. Kiani, A.B. Kiani, S.A. Khan, S. ur Rehmana, Q.U. Khan, I. Mahmood, L. Zhu, Facile synthesis of Gd and Sn co-doped BiFeO3 supported on nitrogen doped graphene for enhanced photocatalytic activity, J. Phys. Chem. Solids 130 (2019) 222–229. [20] L. Durai, B. Moorthy, C.I. Thomas, D.K. Kim, K.K. Bharathi, Electrochemical properties of BiFeO3 nanoparticles: anode material for sodium-ion battery application, Mater. Sci. Semicond. Process. 68 (2017) 165–171. [21] V.V. Jadhav, M.K. Zate, S. Liu, M. Naushad, R.S. Mane, K.N. Hui, S.H. Han, Mixedphase bismuth ferrite nanoflake electrodes for supercapacitor application, Appl. Nanosci. 6 (4) (2016) 511–519. [22] W. Niu, X. Bi, G. Wang, X. Sun, TiO2 gel thin film doped Ce and Sm preparation and cyclic voltammetry characteristics, Int. J. Electrochem. Sci 8 (2013) 11943–11950. [23] F. Zhang, X. Zeng, D. Bi, K. Guo, Y. Yao, S. Lu, Dielectric, ferroelectric, and magnetic properties of Sm-doped BiFeO3 ceramics prepared by a modified solid-statereaction method, Materials 11 (11) (2018) 2208. [24] C. Yu, G. Viola, D. Zhang, K. Zhou, V. Koval, A. Mahajan, H. Yan, Phase evolution and electrical behaviour of samarium-substituted bismuth ferrite ceramics, J. Eur. Ceram. Soc. 38 (4) (2018) 1374–1380. [25] J. Zhu, D. Xiao, W. Zhang, J. Zhu, Z. Qian, Epitaxial or high-oriented platinum thin films grown on various substrates by the RF magnetron sputtering technique, Physica Status Solidi. A, Appl. Res. 139 (1) (1993) K17–K20. [26] P.M. Deleuze, A. Mahmoud, B. Domenichini, C. Dupont, Theoretical investigation of the platinum substrate influence on BaTiO 3 thin film polarisation, Phys. Chem. Chem. Phys. 21 (8) (2019) 4367–4374. [27] M. Sakar, S. Balakumar, P. Saravanan, S.N. Jaisankar, Annealing temperature mediated physical properties of bismuth ferrite (BiFeO3) nanostructures synthesized by a novel wet chemical method, Mater. Res. Bull. 48 (8) (2013) 2878–2885. [28] P. Godara, A. Agarwal, N. Ahlawat, S. Sanghi, Crystal structure refinement, dielectric and magnetic properties of Sm modified BiFeO3 multiferroic, J. Mol. Struct. 1097 (2015) 207–213. [29] V.S. Puli, D.K. Pradhan, R.K. Katiyar, I. Coondoo, N. Panwar, P. Misra, R.S. Katiyar, Photovoltaic effect in transition metal modified polycrystalline BiFeO3 thin films, J. Phys. D Appl. Phys. 47 (7) (2014) 075502. [30] C.S. Tu, C.S. Chen, P.Y. Chen, H.H. Wei, V.H. Schmidt, C.Y. Lin, J.M. Lee, Enhanced photovoltaic effects in A-site samarium doped BiFeO3 ceramics: the roles of domain structure and electronic state, J. Eur. Ceram. Soc. 36 (5) (2016) 1149–1157. [31] W. Sun, J.F. Li, Q. Yu, L.Q. Cheng, Phase transition and piezoelectricity of sol–gelprocessed Sm-doped BiFeO 3 thin films on Pt (111)/Ti/SiO 2/Si substrates, J. Mater. Chem. C 3 (9) (2015) 2115–2122. [32] X. Xu, T. Guoqiang, R. Huijun, X. Ao, Structural, electric and multiferroic properties of Sm-doped BiFeO3 thin films prepared by the sol–gelprocess, Ceram. Int. 39 (6) (2013) 6223–6228. [33] C. Anthonyraj, M. Muneeswaran, S.G. Raj, N.V. Giridharan, V. Sivakumar, G. Senguttuvan, Effect of samarium doping on the structural, optical and magnetic properties of sol–gel processed BiFeO 3 thin films, J. Mater. Sci. Mater. Electron. 26 (1) (2015) 49–58. [34] P. Kumar, P. Chand, Structural, electric transport response and electro-strain-polarization effect in La and Ni modified bismuth ferrite nanostructures, J. Alloy. Comp. 748 (2018) 504–514. [35] P. Veluswamy, S. Sathiyamoorthy, P. Santhoshkumar, G. Karunakaran, C.W. Lee, D. Kuznetsov, H. Ikeda, Sono-synthesis approach of reduced graphene oxide for ammonia vapour detection at room temperature, Ultrason. Sonochem. 48 (2018) 555–566. [36] A. Thakur, P. Thakur, J.H. Hsu, Smart magnetodielectric nano-materials for the very high frequency applications, J. Alloy. Comp. 509 (17) (2011) 5315–5319. [37] S.K. Gore, R.S. Mane, M. Naushad, S.S. Jadhav, M.K. Zate, Z.A. Alothman, B.K. Hui, Influence of Bi 3+-doping on the magnetic and Mössbauer properties of spinel cobalt ferrite, Dalton Trans. 44 (14) (2015) 6384–6390. [38] B. Andrzejewski, K. Chybczynska, B. Hilczer, M. Blaszyk, T. Lucinski, M. Matczak, L. Kepinski, Controlled growth of bismuth ferrite multiferroic flowers, 1402.1336, (2014). [39] C. Herring, Some theorems on the free energies of crystal surfaces, Phys. Rev. 82 (1) (1951) 87. [40] Y. Fu, T. Wu, J. Wang, J. Zhai, M.J. Shearer, Y. Zhao, S. Jin, Stabilization of the metastable lead iodide perovskite phase via surface functionalization, Nano Lett. 17 (7) (2017) 4405–4414. [41] K. Ravaliya, A. Ravalia, D.D. Pandya, P.S. Solanki, N.A. Shah, Strain and morphology control over electrical behavior of pulsed laser deposited BiFeO3 films, Thin Solid Films 645 (2018) 436–443. [42] C.A. Kumar, G.G. Rao, K. Samatha, S. Bharadwaj, M.P. Dasari, Observation on magnetic variation for low concentration of bismuth and samarium doped Ni–Co ferrites, Karbala Int. J. Modern Sci. 4 (1) (2018) 143–150. [43] H. Wu, P. Xue, Y. Lu, X. Zhu, Microstructural, optical and magnetic characterizations of BiFeO3 multiferroic nanoparticles synthesized via a sol-gel process, J. Alloy. Comp. 731 (2018) 471–477. [44] R. Pandey, C. Panda, P. Kumar, M. Kar, Phase diagram of Sm and Mn co-doped bismuth ferrite based on crystal structure and magnetic properties, J. Sol. Gel Sci. Technol. 85 (1) (2018) 166–177. [45] W. Li, O. Auciello, R.N. Premnath, B. Kabius, Giant dielectric constant dominated by Maxwell–Wagner relaxation in Al 2 O 3/TiO 2 nanolaminates synthesized by atomic
property, magnetic property and electrochemical properties were studied. It can be seen that the dielectric constant of BFfilms is varied between 149 and 182 with samarium doping. In the mean while the remanet magnetization was improved from 0.0007 emu/cm3 to 0.0057 emu/cm3. Through electrochemical studies the BF and the doped films where studied for electrode material in super capacitors, the specific capacitance of the films increased from 40Fg-1 to 184Fg-1. Through all these measurements it can be confirmed that the BF films which have wide range of functional properties can be further enhanced that through samarium doping without any structural transition for use in microelectronic devices. Acknowledgement The Authors are thankful to the Principal and Management of Mepco Schlenk Engineering College for the experimental facilities and support rendered for the research. References [1] W. Eerenstein, N.D. Mathur, J.F. Scott, Multiferroic and magnetoelectric materials, Nature 442 (7104) (2006) 759. [2] J. Wu, Z. Fan, D. Xiao, J. Zhu, J. Wang, Multiferroic bismuth ferrite-based materials for multifunctional applications: ceramic bulks, thin films and nanostructures, Prog. Mater. Sci. 84 (2016) 335–402. [3] J. Wei, Y. Liu, X. Bai, C. Li, Y. Liu, Z. Xu, B. Dkhil, Crystal structure, leakage conduction mechanism evolution and enhanced multiferroic properties in Y-doped BiFeO3 ceramics, Ceram. Int. 42 (12) (2016) 13395–13403. [4] A. Manzoor, A.M. Afzal, N. Amin, M.I. Arshad, M. Usman, M.N. Rasool, M.F. Khan, Investigation of dielectric and optical properties of structurally modified bismuth ferrite nanomaterials, Ceram. Int. 42 (9) (2016) 11447–11452. [5] D. Tiwari, D.J. Fermin, T.K. Chaudhuri, A. Ray, Solution processed bismuth ferrite thin films for all-oxide solar photovoltaics, J. Phys. Chem. C 119 (11) (2015) 5872–5877. [6] T. Rojac, E. Khomyakova, J. Walker, H. Ursic, A. Bencan, BiFeO3 ceramics and thick films: processing issues and electromechanical properties, Magnetic, Ferroelectric, and Multiferroic Metal Oxides, Elsevier, 2018, pp. 515–525. [7] D. Bilican, E. Menéndez, J. Zhang, P. Solsona, J. Fornell, E. Pellicer, J. Sort, Ferromagnetic-like behaviour in bismuth ferrite films prepared by electrodeposition and subsequent heat treatment, RSC Adv. 7 (51) (2017) 32133–32138. [8] L. Saravanan, M.M. Raja, D. Prabhu, V. Pandiyarasan, H. Ikeda, H.A. Therese, Perpendicular magnetic anisotropy in Mo/Co2FeAl0. 5Si0. 5/MgO/Mo multilayers with optimal Mo buffer layer thickness, J. Magn. Magn. Mater. 454 (2018) 267–273. [9] L. Saravanan, D. Prabhu, V. Pandiyarasan, H. Ikeda, H.A. Therese, Impact of MgO thickness on the perpendicular magnetic anisotropy of Mo/Co2FeAl/MgO/Mo multilayers with improved annealing stability, Mater. Res. Bull. 107 (2018) 118–124. [10] X. Deng, J. Huang, Y. Sun, K. Liu, R. Gao, W. Cai, C. Fu, Effect of processing parameters on the structural, electrical and magnetic properties of BFO thin film synthesized via RF magnetron sputtering, J. Alloy. Comp. 684 (2016) 510–515. [11] P.V. Mane, N.B. Shinde, I.M. Mulla, R.R. Koli, A.R. Shelke, M.M. Karanjkar, N.G. Deshpande, Bismuth ferrite thin film as an efficient electrode for photocatalytic degradation of Methylene blue dye, Mater. Res. Express 6 (2) (2018) 026426. [12] Z.Z. Jiang, Z. Guan, N. Yang, P.H. Xiang, R.J. Qi, R. Huang, C.G. Duan, Epitaxial growth of BiFeO3 films on SrRuO3/SrTiO3, Mater. Char. 131 (2017) 217–223. [13] P. Jalkanen, V. Tuboltsev, B. Marchand, A. Savin, M. Puttaswamy, M. Vehkamäki, J. Räisänen, Magnetic properties of polycrystalline bismuth ferrite thin films grown by atomic layer deposition, J. Phys. Chem. Lett. 5 (24) (2014) 4319–4323. [14] A. Iljinas, V. Stankus, Structural and ferroelectric properties of bismuth ferrite thin films deposited by direct current reactive magnetron sputtering, Thin Solid Films 601 (2016) 106–110. [15] A.B. Mei, Y. Tang, J. Schubert, D. Jena, H. Xing, D.C. Ralph, D.G. Schlom, Selfassembly and properties of domain walls in BiFeO3 layers grown via molecularbeam epitaxy, Apl. Mater. 7 (7) (2019) 071101. [16] A. Bala, S.B. Majumder, M. Dewan, A.R. Chaudhuri, Hydrogen sensing characteristics of perovskite based calcium doped BiFeO3 thin films, Int. J. Hydrogen Energy 44 (33) (2019) 18648–18656.
11
Ceramics International xxx (xxxx) xxx–xxx
R. Anlin Golda, et al.
layer deposition, Appl. Phys. Lett. 96 (16) (2010) 162907. [46] X. Xu, T. Guoqiang, R. Huijun, X. Ao, Structural, electric and multiferroic properties of Sm-doped BiFeO3 thin films prepared by the sol–gelprocess, Ceram. Int. 39 (6) (2013) 6223–6228. [47] K. Ulutas, D. Deger, S. Yakut, Thickness dependence of the dielectric properties of thermally evaporated Sb2Te3 thin films, Journal of Physics: Conference Series, vol 417, IOP Publishing, 2013, p. 012040 No. 1. [48] H. Ji, W. Ren, L. Wang, P. Shi, X. Chen, X. Wu, K.K. Shung, Structure and electrical properties of Na 0.5 Bi 0.5 TiO 3 ferroelectric thick films derived from a polymer modified sol-gel method, IEEE Trans. Ultrason. Ferroelectr. Freq. Control 58 (10) (2011) 2042–2049. [49] D.A.I. Haiyang, C.H.E.N. Zhenping, L.I. Tao, L.I. Yong, Microstructure and properties of Sm-substituted BiFeO3 ceramics, J. Rare Earths 30 (11) (2012) 1123–1128. [50] G.S. Arya, R.K. Sharma, N.S. Negi, Enhanced magnetic properties of Sm and Mn codoped BiFeO3 nanoparticles at room temperature, Mater. Lett. 93 (2013) 341–344. [51] N. Dutta, S.K. Bandyopadhyay, S. Rana, P. Sen, A.K. Himanshu, Remarkably high value of capacitance in BiFeO3 Nanorod, 1309.5690, (2013). [52] A. Sarkar, A.K. Singh, D. Sarkar, G.G. Khan, K. Mandal, Three-dimensional
[53]
[54] [55]
[56]
[57]
12
nanoarchitecture of BiFeO3 anchored TiO2 nanotube arrays for electrochemical energy storage and solar energy conversion, ACS Sustain. Chem. Eng. 3 (9) (2015) 2254–2263. P. Godara, A. Agarwal, N. Ahlawat, S. Sanghi, Crystal structure refinement, dielectric and magnetic properties of Sm modified BiFeO3 multiferroic, J. Mol. Struct. 1097 (2015) 207–213. D.A.I. Haiyang, C.H.E.N. Zhenping, L.I. Tao, L.I. Yong, Microstructure and properties of Sm-substituted BiFeO3 ceramics, J. Rare Earths 30 (11) (2012) 1123–1128. Z. Xiao, Y. Yuan, Y. Shao, Q. Wang, Q. Dong, C. Bi, J. Huang, Giant switchable photovoltaic effect in organometal trihalide perovskite devices, Nat. Mater. 14 (2) (2015) 193. T.Y. Yang, G. Gregori, N. Pellet, M. Grätzel, J. Maier, The significance of ion conduction in a hybrid organic–inorganic lead‐iodide‐based perovskite photosensitizer, Angew. Chem. Int. Ed. 54 (27) (2015) 7905–7910. C.H. Hendon, R.X. Yang, L.A. Burton, A. Walsh, Assessment of polyanion (BF 4− and PF 6−) substitutions in hybrid halide perovskites, J. Mater. Chem. 3 (17) (2015) 9067–9070.