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New La1−xCr0.7xEu0.3xFeO3 nanoparticles: Synthesis via wet chemical route, structural characterization for magnetic and dielectric behavior evaluation
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CERAMICS INTERNATIONAL
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New La1 xCr0.7xEu0.3xFeO3 nanoparticles: Synthesis via wet chemical route, structural characterization for magnetic and dielectric behavior evaluation Shokat Nawaza, Huma Malikb, Muhammad Farooq Warsia, Muhammad Shahida, Imran Shakirc, Abdul Wadooda,n, Muhammad Azhar Khanb,n a
Department of Chemistry, The Islamia University of Bahawalpur, Bahawalpur-63100, Pakistan b Department of Physics, The Islamia University of Bahawalpur, Bahawalpur-63100, Pakistan c Deanship of Scientific Research, College of Engineering, PO Box 800, King Saud University, Riyadh 11421, Saudi Arabia Received 11 January 2015; accepted 26 January 2015
Abstract La1 xCr0.7xEu0.3xFeO3 nanoparticles were fabricated by micro-emulsion route. The value of x was kept in the range of 0.00 to 0.04. The synthesized nanoparticles were then characterized by X-ray diffraction (XRD), Fourier transform infra-red spectroscopy (FTIR) and scanning electron microscopy (SEM). The XRD confirmed the orthorhombic phase and estimated the crystallite size in the range of 30–90 nm. The nanoparticles estimated by SEM were in the range 60–100 nm. The XRD data was further supported by FTIR spectrum. The main FTIR bands observed were: Fe–O (418 cm 1), Cr–O (545 cm 1), La–O (570 cm 1) and Eu–O (416 cm 1). After structural elucidation, the La1 xCr0.7xEu0.3xFeO3 nanoparticles were subjected to magnetic parameters and dielectric behavior evaluation. The replacement of La3 þ ions, with Cr3 þ and rare earth Eu3 þ exhibited interesting magnetic and dielectric behavior. The LaFeO3 nanoparticles without any dopants showed the paramagnetic behavior. However as the La3 þ was substituted by Cr3 þ and Eu3 þ , the ferromagnetic behavior was observed. Similarly the dielectric parameters were reduced by the replacement of La3 þ ions with Cr3 þ and Eu3 þ metal ions. The maximum magnetic parameters were observed for La0.6Cr0.28Eu0.12FeO3 (Coercivity0.04 T, Saturation magnetization 0.728 emug 1 and Retentivity 0.0.6783 emug 1). The maximum dielectric constant (23.52 at 1.5 10 2 GHz) was observed for LaFeO3 nanoparticles, while the minimum value of dielectric constant (10.32 at 1.5 10 2 GHz) was exhibited by La0.8Cr0.14Eu0.06FeO3 nanoparticles. & 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: C. Magnetic properties; D. Perovskites; Nanoparticles; SEM; Dielectric parameters
1. Introduction Nanoscience and nanotechnology is attracting the attention of the researchers due to their versatile applications that covers approximately all field of life [1]. Its applications ranges from medical diagnosis and therapy [2], catalysis [3], energy storage [4] as well as energy conversion devices [5] etc. Nanoparticles, in most of the cases, behave entirely different from their bulk counter parts. The well known example is the presence of Plasmon resonance band in metal nanoparticles that is normally n
Corresponding authors. Tel.: þ92 3335121491; fax: þ 92 62 9255474. E-mail addresses: [email protected], [email protected] (M.A. Khan).
absent in the bulk metals spectra [2]. Among various nanoparticles, the transition metals nanoparticles have significant importance in various technological devices due to variable oxidation state that is the inherent feature of transition metals and make the metals very rich in chemistry [6]. The combination of transition metals with rare earth metals makes the materials richer and more attractive for researchers and engineers. For example the LaFeO3 has rare earth (La) and transition metal (Fe), is a well known example of perovskite. The applications of LaFeO3 perovskite in numerous technologies are attributed to the structural features of LaFeO3 [7–10].The LaFeO3 has been studied recently for various applications. The main application domain of LaFeO3 and its derivates has been the solid oxide fuel cells. Pecchi et al. [11]] reported that Ca2 þ
http://dx.doi.org/10.1016/j.ceramint.2015.01.129 0272-8842/& 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: S. Nawaz, et al., New La1 xCr0.7xEu0.3xFeO3 nanoparticles: Synthesis via wet chemical route, structural characterization for magnetic..., Ceramics International (2015), http://dx.doi.org/10.1016/j.ceramint.2015.01.129
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substitution improved the redox properties of LaFeO3. Kong and Shen [12] observed that Ca2 þ incorporation into LaFeO3 is an effective way to enhance sensitivity to ethanol. All these recent reports described the effect of transition metals and some other metals effect on various redox and related properties of LaFeO3 perovskite. Rare earth doping in LaFeO3 has also been reported for various applications especially the dielectric parameters. Recently we reported the effect of Eu3 þ on structural and dielectric behavior of LaFeO3 nanoparticles [13]. However, the combined effect of rare earth metals with transition metals on LaFeO3 is not frequently reported. Here in this article, we plan to explore the combined effect of rare earth (Eu3 þ ) and transition metal (Cr3 þ ) on structural, magnetic and dielectric behavior of LaFeO3 nanoparticles fabricated via cheap microemulsion route. 2. Materials and methods Following chemicals were used as received without any further purification for synthesis of Cr3 þ and Eu3 þ doped LaFeO3 nanoparticles (La1 xCr0.7xEu0.3xFeO3): EuCl3 6H2O (Sigma-Aldrich, 99.9%), Fe(NO3)3 9H2O (Merck, 98%),Cr (NO3)3 9H2O (sigma-Aldrich, 99.9%) and NH3(BDH, 35%). Wet chemical route i.e. micro-emulsion route [6] was followed for the synthesis of required La1 xCr0.7xEu0.3xFeO3 nanoparticles. This route involved the preparation of aqueous solutions with required accurate concentrations of all the metal salts used in the synthesis. The aqueous solutions were then mixed at room temperature. The temperature was elevated to 50 1C. At this elevated temperature the aqueous solution of surfactant cetyltrimethylammoniumbromide (CTAB). Aqueous ammonia was used to raise the pH to 10. The stirring was done for 4 h. Washing with deionized water was carried out to remove all the water soluble impurities and for neutralization purpose. The drying, grinding and annealing was carried out to get the final powdered La1 xCr0.7xEu0.3xFeO3 nanoparticles. 3. Results and discussion 3.1. XRD analysis X-ray diffraction analysis for La1 xCr0.7xEu0.3xFeO3 nanoparticles was carried out at Philips X’ Pert PRO 3040/60 diffractometer using Cu Kα as radiation source. The XRD patterns for all samples of La1 xCr0.7xEu0.3xFeO3 are shown in Fig. 1. The major reflections were observed at two theta values 23.001 [002], 25.281 [111], 32.701 [112], 33.961 [021], 40.271 [022], 46.911 [002], 52.731 [131], 58.111 [230] and 68.351 [040]. This data was found compatible with standard diffraction patterns of JCPDS (ICSD-01–074-2203). From XRD data the lattice parameters (a, b and c), cell volume, bulk density and crystallite size was also determined (Table 1). All the lattice parameters were decreased as the La3 þ was substituted with Cr3 þ and Eu3 þ ions. This decrease is attributed to the larger ionic radius of La3 þ ( 1.03 Å), whereas both Cr3 þ (0.64 Å) and Eu3 þ (0.947 Å) have ionic radii less than 1.00 Å. The cell volume therefore was also found to decrease. The
Fig. 1. XRD patterns of “La1 x Cr0.7x Eu0.3xFeO3” nanoparticles.
Table 1 Various lattice parameters and physical parameters for La1 x Cr0.7x Eu0.3xFeO3 nanoparticles. x (mole) 0.0 0.01 0.02 0.03 0.04 Cr (mole) 0.0 0.07 0.14 0.21 0.28 Eu (mole) 0.0 0.03 0.06 0.09 0.12 Lattice constant a (Å) 5.5545 5.5303 5.5109 5.4843 5.4798 Lattice constant b (Å) 5.5703 5.5567 5.5364 5.5164 5.4890 Lattice constant c(Å) 7.8647 7.8456 7.8345 7.8123 7.7987 243.3356 241.0969 239.0348 236.3501 234.5741 Cell volume (Å)3 Bulk density (g/cm3) 1.14 1.17 1.23 1.25 1.29 Crystalline size (nm) 56.76 41.98335 46.39727 33.56 89.56
crystallite size was determined by Sherrer formula and was found in the range of 30–90 nm. This range is compatible with the particles size determined by SEM images. The bulk density also followed a regular trend as the La3 þ was substituted with Cr3 þ and Eu3 þ ions. Similar trend has been already reported in our previous reports for the similar compounds of nanosized [14–16]. 3.2. FTIR analysis FTIR spectrum of La0.6Cr0.28Eu0.12FeO3 nanoparticles was recorded on Nexus 470 spectrometer at room temperature (Fig. 2). The IR bands of Fe–O, Eu–O, La–O, Cr–O and were observed at 418 cm 1, 416 cm 1, 570 cm 1 and 545 cm 1, respectively. These IR band positions are compatible with already reported values of corresponding metal–oxygen IR bands [17,18]. 3.3. SEM images SEM analysis for the La1 xCr0.7xEu0.3xFeO3 nanoparticles was recorded on Jeol JSM-6490A electron microscope. Typically the SEM image of La1 xCr0.7xEu0.3xFeO3 nanoparticles
Please cite this article as: S. Nawaz, et al., New La1 xCr0.7xEu0.3xFeO3 nanoparticles: Synthesis via wet chemical route, structural characterization for magnetic..., Ceramics International (2015), http://dx.doi.org/10.1016/j.ceramint.2015.01.129
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Fig. 4. Hysteresis loops of “La1 xCr0.7xEu0.3xFeO3” nanoparticles.
Fig. 2. FTIR spectra of “La0.6Cr0.28Eu0.12FeO3” nanoparticles.
Table 2 Various magnetic parameters for La1 x Cr0.7x Eu0.3xFeO3 nanoparticles. S. Composition of no. nanoparticles
Coercivity “Hc”(Tesla)
Retentivity “Mr”(emu/g)
Magnetization “Ms” (emu/g)
1. 2. 3. 4. 5.
0.01 0.02 0.04 0.03 0.04
0.00768 0.0392 0.4641 0.3002 0.6783
0.027 0.141 0.496 0.321 0.728
LaFeO3 La0.9Cr0.07Eu0.03FeO3 La0.8Cr0.14Eu0.06FeO3 La0.7Cr0.21Eu0.09FeO3 La0.6Cr0.28Eu0.12FeO3
is shown in Fig. 3. It is clear from the Figure, that the particles are not well dispersed, they are found to aggregate. This aggregation might be due to inefficient sample preparation for SEM analysis. The particles are approximately spherical in shape. The average particles diameter estimated by SEM was 70–110 nm. This is found o be compatible with the crystallite size determined by XRD data [16].
magnetic field was kept from –2.5 T to þ 2.5 T. The hysteresis loops measured in the said range for all compositions of La1 xCr0.7xEu0.3xFeO3 nanoparticles are shown in the Fig. 4. The Fig. 4 shows that, the LaFeO3 nanoparticles exhibited weak ferromagnetic behavior [19]. However as the La3 þ was substituted with Cr3 þ and Eu3 þ ions, the ferromagnetic character occurred. Various magnetic parameters such as saturation magnetization (Ms), retentivity (Mr) and coercivity (Hc) were extracted and are given in the Table 2. The effect of Cr3 þ and Eu3 þ ions on these parameters is summarized in Fig. 5. This Figure shows that as the La3 þ contents were decreased and those of Cr3 þ and Eu3 þ were increased, the Ms and Mr values were increased. However the value of Hc was first increased and then decreased. The maximum values of these parameters were observed by La0.6Cr0.28Eu0.12FeO3 nanoparticles i.e. Coercivity 0.04 T, Saturation magnetization 0.728 emug 1 and Retentivity 0.0.6783 emug 1. The enhancement in the magnetic parameters may be attributed to the uncompensated surface spins due to the reduction in the particle size by the incorporation of Eu3 þ cations in these nanoparticles [19,20].
3.4. Magnetic measurements
3.5. Dielectric parameters
The magnetic properties of La1 xCr0.7xEu0.3xFeO3 nanoparticles were measured by using vibrating sample magnetometer (VSM) Lakeshore-74071 at 298 K. The range of applied
Dielectric constant (ε) is the ratio of the charge stored with free space as the dielectric to that of stored in the materials under investigation. Actually the value of “ε” determines the
Fig. 3. Typical SEM image of La1 x Cr0.7x Eu0.3xFeO3 nanoparticles.
Please cite this article as: S. Nawaz, et al., New La1 xCr0.7xEu0.3xFeO3 nanoparticles: Synthesis via wet chemical route, structural characterization for magnetic..., Ceramics International (2015), http://dx.doi.org/10.1016/j.ceramint.2015.01.129
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Fig. 5. Simultaneous effect of Cr3 þ and Eu3 þ on Ms, Mr and Hc of “La1 xCr0.7xEu0.3xFeO3” nanoparticles.
frequency region. This type of behavior is attributed to the increased interfacial space charge polarization and the hopping conduction mechanism. The electron hopping can follow the electric field fluctuations at higher frequencies [23,24]. The values of dielectric constant at selected frequencies for all composition of nanoparticles are given in Table 3. This table shows that the maximum value of dielectric constant (ε ¼ 23.519) was observed for LaFeO3. About 1.6 fold reduction in dielectric constant was observed as the La3 þ was substituted by Cr3 þ and Eu3 þ . The minimum value of dielectric constant was observed 10.32 at 1.5 10 2 GHz by La0.8Cr0.14Eu0.06FeO3 nanoparticles. The effect of Cr3 þ and Eu3 þ is summarized in Fig. 7. This figure shows that generally the dielectric constant was decreased with replacement of La3 þ with Cr3 þ and Eu3 þ ions. Both Cr3 þ and Eu3 þ are supposed to have different effects on the dielectric constant. However the dominant effect of Eu3 þ was observed, as the rare earth usually decrease the dielectric parameters. This effect of rare earth cations is attributed to their inherent behavior of increasing resistivity. Such type of behavior has been recently observed by our group [13]. There are several other reports that discussed the increased resistivity by the rare earth cations [25,26]. Table 3 Values of dielectric constant at selected frequencies for various compositions of La1 x Cr0.7x Eu0.3xFeO3 nanoparticles. S. no.
1. 2. 3. 4. 5.
Composition
LaFeO3 La0.9Cr0.07Eu0.03FeO3 La0.8Cr0.14Eu0.06FeO3 La0.7Cr0.21Eu0.09FeO3 La0.6Cr0.28Eu0.12FeO3
Dielectric constant 0.0156 GHz
1.5 GHz
3.0 GHZ
23.51965 11.3214 10.3214 14.4071 14.3204
23.1492 10.0668 9.0668 13.1441 12.0943
22.5348 9.2800 8.2800 11.6709 10.4893
Fig. 6. The variation of dielectric constant with frequency of “La1 x Cr0.7x Eu0.3xFeO3” nanoparticles.
electrostatic energy stored per unit volume for unit potential gradient. The accurate measurements of dielectric parameters and electrical properties of the materials is necessary for the scientists and engineers for manufacturing process of various electronic devices / appliances. The dielectric parameters for the La1 xCr0.7xEu0.3xFeO3 nanoparticles were measured in the frequency range 1.0 106 Hz–3.0 109 Hz [21]. Two aspects of dielectric constant (and other dielectric parameters) were evaluated. The effect of frequency on the dielectric constant is shown in Fig. 6. It is clear from the Figure that the value of dielectric constant decreased as the frequency was increased. Higher values of ε at lower frequencies are justified by the contribution of all the four types of polarization i.e. (i) space charge, (ii) dipolar, (iii) ionic and (iv) electronic contributions [22]. However the value dielectric constant decreased rapidly in the low
Fig. 7. The variation of dielectric constant with Cr3 þ and Eu3 þ contents for “La1 x Cr0.7x Eu0.3xFeO3” nanoparticles.
Please cite this article as: S. Nawaz, et al., New La1 xCr0.7xEu0.3xFeO3 nanoparticles: Synthesis via wet chemical route, structural characterization for magnetic..., Ceramics International (2015), http://dx.doi.org/10.1016/j.ceramint.2015.01.129
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4. Conclusions A very cheap and facile route was adopted for fabricating the La1 xCr0.7xEu0.3xFeO3 nanoparticles in the range of 70–110 nm. XRD and FTIR confirmed the orthorhombic phase. The LaFeO3 nanoparticles exhibited paramagnetic behavior. However the substitution of La3 þ with Cr3 þ and Eu3 þ optimized the magnetic character. La0.6Cr0.28Eu0.12FeO3 particles showed the maximum magnetic parameters: Hc 0.04 T, Ms 0.728 emug 1 and Mr 0.0.6783 emug 1. The maximum dielectric constant (23.52) was shown by LaFeO3 at 1.5 10–2 GHz, while the minimum value of dielectric constant (10.32 at 1.5 10–2 GHz) was shown by La0.8Cr0.14Eu0.06FeO3 nanoparticles. Acknowledgement Dr. Imran Shakir is thankful to the deanship of scientific research, King Saud University for research group project RGP-312. References [1] G. Reiss, A. Hutten, Magnetic nanoparticles: applications beyond data storage, Nat. Mater. 4 (2005) 725–726. [2] M.F. Warsi, R.W. Adams, S.B. Duckett, V. Chechik, Gd-functionalised Au nanoparticles as targeted contrast agents in MRI: relaxivity enhancement by polyelectrolyte coating, Chem. Commun. 46 (2010) 451–453. [3] C. Ragupathi, J. Judith Vijaya, S. Narayanan, S.K. Jesudoss, L. John Kennedy, Highly selective oxidation of benzyl alcohol to benzaldehyde with hydrogen peroxide by cobalt aluminate catalysis: a comparison of conventional and microwave methods, Ceram. Int. 41 (2015) 2069–2080. [4] M. Shahid, J. Liu, Z. Ali, I. Shakir, M.F. Warsi, Structural and electrochemical properties of single crystalline MoV2O8 nanowires for energy storage devices, J. Power Sources 230 (2013) 277–281. [5] Y. Meng, Y. Lin, Y. Lin, Electrodeposition for the synthesis of ZnO nanorods modified by surface attachment with ZnO nanoparticles and their dye-sensitized solar cell applications, Ceram. Int. 40 (2014) 1693–1698. [6] M. Azhar Khan, K. Khan, A. Mahmood, G. Murtaza, M.N. Akhtar, I. Ali, M. Shahid, I. Shakir, M. Farooq Warsi, Nanocrystalline La1 xSrxCo1 yFeyO3 perovskites fabricated by the micro-emulsion route for high frequency response devices fabrications, Ceram. Int. 40 (2014) 13211–13216. [7] S. Petrović, A. Terlecki-Baričević, L. Karanović, P. Kirilov-Stefanov, M. Zdujić, V. Dondur, D. Paneva, I. Mitov, V. Rakić, LaMO3 perovskite type oxides: preparation, characterization and catalytic properties in methane deep oxidation, Appl. Catal. B: Environ. 79 (2008) 186–198. [8] M.-H. Hung, M.V.M. Rao, D.-S. Tsai, Microstructures and electrical properties of calcium substituted LaFeO3 as SOFC cathode, Mater. Chem. Phys. 101 (2007) 297–302. [9] X. Liu, B. Cheng, J. Hu, H. Qin, M. Jiang, Semiconducting gas sensor for ethanol based on LaMgxFe1 xO3 nanocrystals, Sens. Actuators B: Chem. 129 (2008) 53–58. [10] D. Bayraktar, F. Clemens, S. Diethelm, T. Graule, J. Van herle, P. Holtappels, Production and properties of substituted LaFeO3-perovskite tubular membranes for partial oxidation of methane to syngas, J. Eur. Ceram. Soc. 27 (2007) 2455–2461.
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Please cite this article as: S. Nawaz, et al., New La1 xCr0.7xEu0.3xFeO3 nanoparticles: Synthesis via wet chemical route, structural characterization for magnetic..., Ceramics International (2015), http://dx.doi.org/10.1016/j.ceramint.2015.01.129
CERAMICS INTERNATIONAL
Ceramics International ] (]]]]) ]]]–]]] www.elsevier.com/locate/ceramint
New La1 xCr0.7xEu0.3xFeO3 nanoparticles: Synthesis via wet chemical route, structural characterization for magnetic and dielectric behavior evaluation Shokat Nawaza, Huma Malikb, Muhammad Farooq Warsia, Muhammad Shahida, Imran Shakirc, Abdul Wadooda,n, Muhammad Azhar Khanb,n a
Department of Chemistry, The Islamia University of Bahawalpur, Bahawalpur-63100, Pakistan b Department of Physics, The Islamia University of Bahawalpur, Bahawalpur-63100, Pakistan c Deanship of Scientific Research, College of Engineering, PO Box 800, King Saud University, Riyadh 11421, Saudi Arabia Received 11 January 2015; accepted 26 January 2015
Abstract La1 xCr0.7xEu0.3xFeO3 nanoparticles were fabricated by micro-emulsion route. The value of x was kept in the range of 0.00 to 0.04. The synthesized nanoparticles were then characterized by X-ray diffraction (XRD), Fourier transform infra-red spectroscopy (FTIR) and scanning electron microscopy (SEM). The XRD confirmed the orthorhombic phase and estimated the crystallite size in the range of 30–90 nm. The nanoparticles estimated by SEM were in the range 60–100 nm. The XRD data was further supported by FTIR spectrum. The main FTIR bands observed were: Fe–O (418 cm 1), Cr–O (545 cm 1), La–O (570 cm 1) and Eu–O (416 cm 1). After structural elucidation, the La1 xCr0.7xEu0.3xFeO3 nanoparticles were subjected to magnetic parameters and dielectric behavior evaluation. The replacement of La3 þ ions, with Cr3 þ and rare earth Eu3 þ exhibited interesting magnetic and dielectric behavior. The LaFeO3 nanoparticles without any dopants showed the paramagnetic behavior. However as the La3 þ was substituted by Cr3 þ and Eu3 þ , the ferromagnetic behavior was observed. Similarly the dielectric parameters were reduced by the replacement of La3 þ ions with Cr3 þ and Eu3 þ metal ions. The maximum magnetic parameters were observed for La0.6Cr0.28Eu0.12FeO3 (Coercivity0.04 T, Saturation magnetization 0.728 emug 1 and Retentivity 0.0.6783 emug 1). The maximum dielectric constant (23.52 at 1.5 10 2 GHz) was observed for LaFeO3 nanoparticles, while the minimum value of dielectric constant (10.32 at 1.5 10 2 GHz) was exhibited by La0.8Cr0.14Eu0.06FeO3 nanoparticles. & 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: C. Magnetic properties; D. Perovskites; Nanoparticles; SEM; Dielectric parameters
1. Introduction Nanoscience and nanotechnology is attracting the attention of the researchers due to their versatile applications that covers approximately all field of life [1]. Its applications ranges from medical diagnosis and therapy [2], catalysis [3], energy storage [4] as well as energy conversion devices [5] etc. Nanoparticles, in most of the cases, behave entirely different from their bulk counter parts. The well known example is the presence of Plasmon resonance band in metal nanoparticles that is normally n
Corresponding authors. Tel.: þ92 3335121491; fax: þ 92 62 9255474. E-mail addresses: [email protected], [email protected] (M.A. Khan).
absent in the bulk metals spectra [2]. Among various nanoparticles, the transition metals nanoparticles have significant importance in various technological devices due to variable oxidation state that is the inherent feature of transition metals and make the metals very rich in chemistry [6]. The combination of transition metals with rare earth metals makes the materials richer and more attractive for researchers and engineers. For example the LaFeO3 has rare earth (La) and transition metal (Fe), is a well known example of perovskite. The applications of LaFeO3 perovskite in numerous technologies are attributed to the structural features of LaFeO3 [7–10].The LaFeO3 has been studied recently for various applications. The main application domain of LaFeO3 and its derivates has been the solid oxide fuel cells. Pecchi et al. [11]] reported that Ca2 þ
http://dx.doi.org/10.1016/j.ceramint.2015.01.129 0272-8842/& 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: S. Nawaz, et al., New La1 xCr0.7xEu0.3xFeO3 nanoparticles: Synthesis via wet chemical route, structural characterization for magnetic..., Ceramics International (2015), http://dx.doi.org/10.1016/j.ceramint.2015.01.129
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substitution improved the redox properties of LaFeO3. Kong and Shen [12] observed that Ca2 þ incorporation into LaFeO3 is an effective way to enhance sensitivity to ethanol. All these recent reports described the effect of transition metals and some other metals effect on various redox and related properties of LaFeO3 perovskite. Rare earth doping in LaFeO3 has also been reported for various applications especially the dielectric parameters. Recently we reported the effect of Eu3 þ on structural and dielectric behavior of LaFeO3 nanoparticles [13]. However, the combined effect of rare earth metals with transition metals on LaFeO3 is not frequently reported. Here in this article, we plan to explore the combined effect of rare earth (Eu3 þ ) and transition metal (Cr3 þ ) on structural, magnetic and dielectric behavior of LaFeO3 nanoparticles fabricated via cheap microemulsion route. 2. Materials and methods Following chemicals were used as received without any further purification for synthesis of Cr3 þ and Eu3 þ doped LaFeO3 nanoparticles (La1 xCr0.7xEu0.3xFeO3): EuCl3 6H2O (Sigma-Aldrich, 99.9%), Fe(NO3)3 9H2O (Merck, 98%),Cr (NO3)3 9H2O (sigma-Aldrich, 99.9%) and NH3(BDH, 35%). Wet chemical route i.e. micro-emulsion route [6] was followed for the synthesis of required La1 xCr0.7xEu0.3xFeO3 nanoparticles. This route involved the preparation of aqueous solutions with required accurate concentrations of all the metal salts used in the synthesis. The aqueous solutions were then mixed at room temperature. The temperature was elevated to 50 1C. At this elevated temperature the aqueous solution of surfactant cetyltrimethylammoniumbromide (CTAB). Aqueous ammonia was used to raise the pH to 10. The stirring was done for 4 h. Washing with deionized water was carried out to remove all the water soluble impurities and for neutralization purpose. The drying, grinding and annealing was carried out to get the final powdered La1 xCr0.7xEu0.3xFeO3 nanoparticles. 3. Results and discussion 3.1. XRD analysis X-ray diffraction analysis for La1 xCr0.7xEu0.3xFeO3 nanoparticles was carried out at Philips X’ Pert PRO 3040/60 diffractometer using Cu Kα as radiation source. The XRD patterns for all samples of La1 xCr0.7xEu0.3xFeO3 are shown in Fig. 1. The major reflections were observed at two theta values 23.001 [002], 25.281 [111], 32.701 [112], 33.961 [021], 40.271 [022], 46.911 [002], 52.731 [131], 58.111 [230] and 68.351 [040]. This data was found compatible with standard diffraction patterns of JCPDS (ICSD-01–074-2203). From XRD data the lattice parameters (a, b and c), cell volume, bulk density and crystallite size was also determined (Table 1). All the lattice parameters were decreased as the La3 þ was substituted with Cr3 þ and Eu3 þ ions. This decrease is attributed to the larger ionic radius of La3 þ ( 1.03 Å), whereas both Cr3 þ (0.64 Å) and Eu3 þ (0.947 Å) have ionic radii less than 1.00 Å. The cell volume therefore was also found to decrease. The
Fig. 1. XRD patterns of “La1 x Cr0.7x Eu0.3xFeO3” nanoparticles.
Table 1 Various lattice parameters and physical parameters for La1 x Cr0.7x Eu0.3xFeO3 nanoparticles. x (mole) 0.0 0.01 0.02 0.03 0.04 Cr (mole) 0.0 0.07 0.14 0.21 0.28 Eu (mole) 0.0 0.03 0.06 0.09 0.12 Lattice constant a (Å) 5.5545 5.5303 5.5109 5.4843 5.4798 Lattice constant b (Å) 5.5703 5.5567 5.5364 5.5164 5.4890 Lattice constant c(Å) 7.8647 7.8456 7.8345 7.8123 7.7987 243.3356 241.0969 239.0348 236.3501 234.5741 Cell volume (Å)3 Bulk density (g/cm3) 1.14 1.17 1.23 1.25 1.29 Crystalline size (nm) 56.76 41.98335 46.39727 33.56 89.56
crystallite size was determined by Sherrer formula and was found in the range of 30–90 nm. This range is compatible with the particles size determined by SEM images. The bulk density also followed a regular trend as the La3 þ was substituted with Cr3 þ and Eu3 þ ions. Similar trend has been already reported in our previous reports for the similar compounds of nanosized [14–16]. 3.2. FTIR analysis FTIR spectrum of La0.6Cr0.28Eu0.12FeO3 nanoparticles was recorded on Nexus 470 spectrometer at room temperature (Fig. 2). The IR bands of Fe–O, Eu–O, La–O, Cr–O and were observed at 418 cm 1, 416 cm 1, 570 cm 1 and 545 cm 1, respectively. These IR band positions are compatible with already reported values of corresponding metal–oxygen IR bands [17,18]. 3.3. SEM images SEM analysis for the La1 xCr0.7xEu0.3xFeO3 nanoparticles was recorded on Jeol JSM-6490A electron microscope. Typically the SEM image of La1 xCr0.7xEu0.3xFeO3 nanoparticles
Please cite this article as: S. Nawaz, et al., New La1 xCr0.7xEu0.3xFeO3 nanoparticles: Synthesis via wet chemical route, structural characterization for magnetic..., Ceramics International (2015), http://dx.doi.org/10.1016/j.ceramint.2015.01.129
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Fig. 4. Hysteresis loops of “La1 xCr0.7xEu0.3xFeO3” nanoparticles.
Fig. 2. FTIR spectra of “La0.6Cr0.28Eu0.12FeO3” nanoparticles.
Table 2 Various magnetic parameters for La1 x Cr0.7x Eu0.3xFeO3 nanoparticles. S. Composition of no. nanoparticles
Coercivity “Hc”(Tesla)
Retentivity “Mr”(emu/g)
Magnetization “Ms” (emu/g)
1. 2. 3. 4. 5.
0.01 0.02 0.04 0.03 0.04
0.00768 0.0392 0.4641 0.3002 0.6783
0.027 0.141 0.496 0.321 0.728
LaFeO3 La0.9Cr0.07Eu0.03FeO3 La0.8Cr0.14Eu0.06FeO3 La0.7Cr0.21Eu0.09FeO3 La0.6Cr0.28Eu0.12FeO3
is shown in Fig. 3. It is clear from the Figure, that the particles are not well dispersed, they are found to aggregate. This aggregation might be due to inefficient sample preparation for SEM analysis. The particles are approximately spherical in shape. The average particles diameter estimated by SEM was 70–110 nm. This is found o be compatible with the crystallite size determined by XRD data [16].
magnetic field was kept from –2.5 T to þ 2.5 T. The hysteresis loops measured in the said range for all compositions of La1 xCr0.7xEu0.3xFeO3 nanoparticles are shown in the Fig. 4. The Fig. 4 shows that, the LaFeO3 nanoparticles exhibited weak ferromagnetic behavior [19]. However as the La3 þ was substituted with Cr3 þ and Eu3 þ ions, the ferromagnetic character occurred. Various magnetic parameters such as saturation magnetization (Ms), retentivity (Mr) and coercivity (Hc) were extracted and are given in the Table 2. The effect of Cr3 þ and Eu3 þ ions on these parameters is summarized in Fig. 5. This Figure shows that as the La3 þ contents were decreased and those of Cr3 þ and Eu3 þ were increased, the Ms and Mr values were increased. However the value of Hc was first increased and then decreased. The maximum values of these parameters were observed by La0.6Cr0.28Eu0.12FeO3 nanoparticles i.e. Coercivity 0.04 T, Saturation magnetization 0.728 emug 1 and Retentivity 0.0.6783 emug 1. The enhancement in the magnetic parameters may be attributed to the uncompensated surface spins due to the reduction in the particle size by the incorporation of Eu3 þ cations in these nanoparticles [19,20].
3.4. Magnetic measurements
3.5. Dielectric parameters
The magnetic properties of La1 xCr0.7xEu0.3xFeO3 nanoparticles were measured by using vibrating sample magnetometer (VSM) Lakeshore-74071 at 298 K. The range of applied
Dielectric constant (ε) is the ratio of the charge stored with free space as the dielectric to that of stored in the materials under investigation. Actually the value of “ε” determines the
Fig. 3. Typical SEM image of La1 x Cr0.7x Eu0.3xFeO3 nanoparticles.
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Fig. 5. Simultaneous effect of Cr3 þ and Eu3 þ on Ms, Mr and Hc of “La1 xCr0.7xEu0.3xFeO3” nanoparticles.
frequency region. This type of behavior is attributed to the increased interfacial space charge polarization and the hopping conduction mechanism. The electron hopping can follow the electric field fluctuations at higher frequencies [23,24]. The values of dielectric constant at selected frequencies for all composition of nanoparticles are given in Table 3. This table shows that the maximum value of dielectric constant (ε ¼ 23.519) was observed for LaFeO3. About 1.6 fold reduction in dielectric constant was observed as the La3 þ was substituted by Cr3 þ and Eu3 þ . The minimum value of dielectric constant was observed 10.32 at 1.5 10 2 GHz by La0.8Cr0.14Eu0.06FeO3 nanoparticles. The effect of Cr3 þ and Eu3 þ is summarized in Fig. 7. This figure shows that generally the dielectric constant was decreased with replacement of La3 þ with Cr3 þ and Eu3 þ ions. Both Cr3 þ and Eu3 þ are supposed to have different effects on the dielectric constant. However the dominant effect of Eu3 þ was observed, as the rare earth usually decrease the dielectric parameters. This effect of rare earth cations is attributed to their inherent behavior of increasing resistivity. Such type of behavior has been recently observed by our group [13]. There are several other reports that discussed the increased resistivity by the rare earth cations [25,26]. Table 3 Values of dielectric constant at selected frequencies for various compositions of La1 x Cr0.7x Eu0.3xFeO3 nanoparticles. S. no.
1. 2. 3. 4. 5.
Composition
LaFeO3 La0.9Cr0.07Eu0.03FeO3 La0.8Cr0.14Eu0.06FeO3 La0.7Cr0.21Eu0.09FeO3 La0.6Cr0.28Eu0.12FeO3
Dielectric constant 0.0156 GHz
1.5 GHz
3.0 GHZ
23.51965 11.3214 10.3214 14.4071 14.3204
23.1492 10.0668 9.0668 13.1441 12.0943
22.5348 9.2800 8.2800 11.6709 10.4893
Fig. 6. The variation of dielectric constant with frequency of “La1 x Cr0.7x Eu0.3xFeO3” nanoparticles.
electrostatic energy stored per unit volume for unit potential gradient. The accurate measurements of dielectric parameters and electrical properties of the materials is necessary for the scientists and engineers for manufacturing process of various electronic devices / appliances. The dielectric parameters for the La1 xCr0.7xEu0.3xFeO3 nanoparticles were measured in the frequency range 1.0 106 Hz–3.0 109 Hz [21]. Two aspects of dielectric constant (and other dielectric parameters) were evaluated. The effect of frequency on the dielectric constant is shown in Fig. 6. It is clear from the Figure that the value of dielectric constant decreased as the frequency was increased. Higher values of ε at lower frequencies are justified by the contribution of all the four types of polarization i.e. (i) space charge, (ii) dipolar, (iii) ionic and (iv) electronic contributions [22]. However the value dielectric constant decreased rapidly in the low
Fig. 7. The variation of dielectric constant with Cr3 þ and Eu3 þ contents for “La1 x Cr0.7x Eu0.3xFeO3” nanoparticles.
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4. Conclusions A very cheap and facile route was adopted for fabricating the La1 xCr0.7xEu0.3xFeO3 nanoparticles in the range of 70–110 nm. XRD and FTIR confirmed the orthorhombic phase. The LaFeO3 nanoparticles exhibited paramagnetic behavior. However the substitution of La3 þ with Cr3 þ and Eu3 þ optimized the magnetic character. La0.6Cr0.28Eu0.12FeO3 particles showed the maximum magnetic parameters: Hc 0.04 T, Ms 0.728 emug 1 and Mr 0.0.6783 emug 1. The maximum dielectric constant (23.52) was shown by LaFeO3 at 1.5 10–2 GHz, while the minimum value of dielectric constant (10.32 at 1.5 10–2 GHz) was shown by La0.8Cr0.14Eu0.06FeO3 nanoparticles. Acknowledgement Dr. Imran Shakir is thankful to the deanship of scientific research, King Saud University for research group project RGP-312. References [1] G. Reiss, A. Hutten, Magnetic nanoparticles: applications beyond data storage, Nat. Mater. 4 (2005) 725–726. [2] M.F. Warsi, R.W. Adams, S.B. Duckett, V. Chechik, Gd-functionalised Au nanoparticles as targeted contrast agents in MRI: relaxivity enhancement by polyelectrolyte coating, Chem. Commun. 46 (2010) 451–453. [3] C. Ragupathi, J. Judith Vijaya, S. Narayanan, S.K. Jesudoss, L. John Kennedy, Highly selective oxidation of benzyl alcohol to benzaldehyde with hydrogen peroxide by cobalt aluminate catalysis: a comparison of conventional and microwave methods, Ceram. Int. 41 (2015) 2069–2080. [4] M. Shahid, J. Liu, Z. Ali, I. Shakir, M.F. Warsi, Structural and electrochemical properties of single crystalline MoV2O8 nanowires for energy storage devices, J. Power Sources 230 (2013) 277–281. [5] Y. Meng, Y. Lin, Y. Lin, Electrodeposition for the synthesis of ZnO nanorods modified by surface attachment with ZnO nanoparticles and their dye-sensitized solar cell applications, Ceram. Int. 40 (2014) 1693–1698. [6] M. Azhar Khan, K. Khan, A. Mahmood, G. Murtaza, M.N. Akhtar, I. Ali, M. Shahid, I. Shakir, M. Farooq Warsi, Nanocrystalline La1 xSrxCo1 yFeyO3 perovskites fabricated by the micro-emulsion route for high frequency response devices fabrications, Ceram. Int. 40 (2014) 13211–13216. [7] S. Petrović, A. Terlecki-Baričević, L. Karanović, P. Kirilov-Stefanov, M. Zdujić, V. Dondur, D. Paneva, I. Mitov, V. Rakić, LaMO3 perovskite type oxides: preparation, characterization and catalytic properties in methane deep oxidation, Appl. Catal. B: Environ. 79 (2008) 186–198. [8] M.-H. Hung, M.V.M. Rao, D.-S. Tsai, Microstructures and electrical properties of calcium substituted LaFeO3 as SOFC cathode, Mater. Chem. Phys. 101 (2007) 297–302. [9] X. Liu, B. Cheng, J. Hu, H. Qin, M. Jiang, Semiconducting gas sensor for ethanol based on LaMgxFe1 xO3 nanocrystals, Sens. Actuators B: Chem. 129 (2008) 53–58. [10] D. Bayraktar, F. Clemens, S. Diethelm, T. Graule, J. Van herle, P. Holtappels, Production and properties of substituted LaFeO3-perovskite tubular membranes for partial oxidation of methane to syngas, J. Eur. Ceram. Soc. 27 (2007) 2455–2461.
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Please cite this article as: S. Nawaz, et al., New La1 xCr0.7xEu0.3xFeO3 nanoparticles: Synthesis via wet chemical route, structural characterization for magnetic..., Ceramics International (2015), http://dx.doi.org/10.1016/j.ceramint.2015.01.129