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A simple method of synthesizing homogeneous La0.1Bi0.9FeO3–BiY2Fe5O12 composite powders
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CERAMICS INTERNATIONAL
Ceramics International 40 (2014) 6301–6305 www.elsevier.com/locate/ceramint
Short communication
A simple method of synthesizing homogeneous La0.1Bi0.9FeO3–BiY2Fe5O12 composite powders Miao Liu, Haibo Yangn, Ying Lin, Yanyan Yang School of Materials Science and Engineering, Shaanxi University of Science and Technology, Xi'an 710021, China Received 9 September 2013; received in revised form 24 September 2013; accepted 24 September 2013 Available online 2 October 2013
Abstract La0.1Bi0.9FeO3–BiY2Fe5O12 (abbreviated as LBFO–BYIG) composites were synthesized via a one-step sol–gel method. The synthesized composite powders were characterized using X-ray diffraction and scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy. The magnetic properties of the as-prepared composite powders were investigated by a vibrating sample magnetometer. The asprepared LBFO–BYIG composite powders show a good homogeneity of the two phases and a good crystallinity. Additionally, the magnetization of LBFO can be improved by the introduction of proper amount of BYIG. & 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: B. Composites; C. Magnetic properties; Homogeneity
1. Introduction Multiferroic materials with coexistence of two or more ferroic order parameters (ferroelectric, ferromagnetic or ferroelastic) have drawn increasing interest due to their potential applications as multifunctional devices such as multiple state memory elements, sensors, actuators and transducers [1]. However, very few mutiferroic materials exist in nature or have been synthesized in the laboratory [2]. More recently, the surge in interest has been further stimulated by the unique room-temperature single-phase multiferroic BiFeO3 (BFO) with high Curie (Tc ¼ 1103 K) and Neel (TN ¼ 643 K) temperatures [3]. But the practical applications of BFO materials have been hindered because of their large leakage current (RT) and weak magnetic behavior as a result of the small amounts of Fe2 þ and oxygen vacancies and their spiral modulated spin structure, respectively [4,5]. Recently, many methods have been employed to improve the magnetization by forming constrained epitaxial films and chemical substitution. For example, Wang et al. have reported the preparation of the BiFeO3–CoFe2O4 composite epitaxial thin films using pulsed laser deposition method [6]. Carvalho et al. have reported the n
Corresponding author. Tel./fax: þ 86 29 86168688. E-mail address: [email protected] (H. Yang).
preparation of the Bi0.7La0.3FeO3 ceramics by a sol–gel method [7]. But the enhancement is limited because they can only suppress or destroy the spin cycloid but cannot change the intrinsic antiferromagnetic nature of BFO-based single-phase materials. An alternative effective way of enhancing the magnetism for the BFO-based multiferroics is to introduce suitable ferrites to form composites [8]. Liu et al. have reported the preparation of CoFe2O4 and 0.7BiFeO3–0.3BaTiO3 separately, where CoFe2O4 was synthesized by a combustion method and 0.7BiFeO3–0.3BaTiO3 by a traditional solid-state method. After preparation of CoFe2O4 and 0.7BiFeO3– 0.3BaTiO3, they were mixed by ball-milling and sintered at 1010 1C for 2 h [8]. However, the electrical properties would deteriorate owing to the low resistivity of CoFe2O4. Y3Fe5O12 (YIG) is known to be a classical microwave ferrite and possesses high magnetization and resistivity. Its sintering temperature can be lowered from 1400 1C to 1000 1C by the substitution of Y3 þ by Bi3 þ to form BiY2Fe5O12. Our group has introduced Y3Fe5O12 and BiY2Fe5O12 into 0.7BiFeO3– 0.3BaTiO3 to form composite to simultaneously enhance the magnetic and ferroelectric properties of 0.7BiFeO3–0.3BaTiO3 due to the high magnetization and resistivity of YIG and BYIG [9,10]. Generally, the strategy to prepare the composite powders is synthesizing single-phase powder individually and then mixing them together by ball milling, which is called
0272-8842/$ - see front matter & 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved. http://dx.doi.org/10.1016/j.ceramint.2013.09.108
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the physical mixing method [11,12]. It is well known that the homogeneity of the composite powders prepared by the physical mixing method is limited. Consequently, the aim of this paper is to synthesize homogeneous LBFO/BYIG composite powders via a one-step sol–gel method. The LBFO/BYIG composite powders were synthesized by calcining the sol containing the starting materials of both LBFO and BYIG at different mass ratios. 2. Experimental procedure To prepare xLBFO–(1 x)BYIG composites (with x=0.9, 0.8, 0.7, and 0.6) using the one-step sol–gel method, reagents of Bi(NO3)3, Fe(NO3)3 9H2O, Y(NO3)3 6H2O, La(NO3)3 6H2O and C6H8O7 H2O were used as starting materials. An aqueous solution of C6H8O7 H2O was prepared in distilled water. Then stoichiometric amounts of Bi(NO3)3, Fe(NO3)3 9H2O, Y(NO3)3 6H2O, and La(NO3)3 6H2O were added into the solution stirred at 80 1C. In order to avoid precipitation and get a homogenous mixture solution, some C2H8N2 was added into the above solution at the same time. After that the reaction solution mixture was dried at 200 1C for 2 h. Black color floppy carbonaceous material was formed after drying, which was called precursor powder. Then the precursor powders were calcined in air to obtain xLBFO–(1 x)BYIG composite powders. The phase composition of LBFO–BYIG composite powders was detected by a X-ray diffractometer (XRD) with Cu Kα radiation (Rigaku D/MAX-2400, Japan). The morphology of the composite powders was analyzed using a scanning electron microscope (SEM; Hitachi S-4800, Japan) equipped with energy-dispersive X-ray spectroscopy (EDS). The magnetic hysteresis loops of the composite powders were measured by a vibrating sample magnetometer 113 (VSM) (Lake Shore 7410, USA). 3. Results and discussion The XRD patterns of the 0.6LBFO–0.4BYIG composite powders with different calcining temperatures ranging from 600 to 800 1C for 4 h are shown in Fig. 1(a). After being heated at 600 1C in air for 4 h, the main diffraction peaks of LBFO and BYIG can be found while the intensities of diffraction peaks are weak indicating that the crystallinity of powder is not good. Although major peaks due to LBFO and BYIG are obviously enhanced for the powders calcined at 700 1C, additional peaks indexed to Fe2O3 are also observed indicating that the formation process of LBFO and BYIG is not complete. With the increase in temperature from 700 to 800 1C, the diffraction peaks from Fe2O3 almost disappear completely and pure phase LBFO and BYIG can be obtained. It indicates that the two phases can co-exist in the synthesized composite powders at 800 1C. The XRD patterns are in excellent correspondence with JCPDS 20-1069 of LBFO and JCPDS 43-0507 of BYIG. All the diffraction peaks can be perfectly indexed to the rhombohedral distorted perovskite structure of LBFO and the cubic structure of YIG.
Fig. 1. (a) XRD patterns of the 0.6LBFO–0.4BYIG composites with different calcining temperatures; (b) XRD patterns of the LBFO–BYIG composites with different LBFO concentrations.
The XRD patterns of the LBFO–BYIG composite powders calcined at 800 1C for 4 h with different BYIG concentrations are shown in Fig. 1(b). It can be clearly seen that only the parent phases of LBFO and BYIG can be found in all the samples. Moreover, the XRD shows that the synthesized powders of LBFO and BYIG have pure rhombohedral distortion perovskite structure and cubic structure, respectively [13]. Within the resolution limit of XRD any other immediate phase cannot be detected. The above powder X-ray diffractograms reveal that LBFO and BYIG phases co-exist after being calcined at 800 1C with a high crystallinity and without any impurity phases. Obviously, by increasing the BYIG concentration, the diffraction peaks of BYIG become strengthened gradually. Fig. 2 shows the morphology of the 0.6LBFO–0.4BYIG composite powders calcined at different temperatures ranging from 600 1C to 800 1C for 4 h. It can be seen that in Fig. 2(a) grains are not well developed. Moreover, the powders are inhomogeneous
M. Liu et al. / Ceramics International 40 (2014) 6301–6305
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Fig. 2. SEM micrographs of the 0.6LBFO–0.4BYIG composite powders calcined at different temperatures: (a) 600 1C, (b) 700 1C, and (c) 800 1C.
Fig. 3. SEM micrographs of the xLBFO–(1 x)BYIG composite powders calcined at 800 1C: (a) x¼ 0.9, (b) x¼ 0.8, (c) x ¼0.7, and (d) x ¼0.6.
and seriously aggregated. With increasing calcining temperature, the composite powders become more and more homogeneous and all the grains are developed better and better, especially those in Fig. 2(c). The morphology of the xLBFO–(1 x)BYIG composite powders calcined at 800 1C for 4 h is shown in Fig. 3. Because the formation temperature of BYIG is higher than that of LBFO [9,14], the small grains (Spot A) are of the BYIG
phase while the large grains (Spot B) are of the LBFO phase. With increasing BYIG concentration, LBFO and BYIG powders become more and more homogeneous and the grains develop better and better. This phenomenon is also consistent with the XRD results. Fig. 4 shows the EDS mapping analysis result of the representative 0.8LBFO–0.2BYIG composite powders. It can be easily found that four different kinds of colors are uniform,
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Fig. 4. EDS mapping analysis result of the 0.8LBFO–0.2BYIG composite powders.
Table 1 Magnetic parameters of the xLBFO–(1 x)BYIG composite powders calcined at 800 1C. x
Hc (G)
Ms (emu/g)
Mr (emu/g)
0.9 0.8 0.7 0.6
3779.81 132.47 67.18 59.96
0.175 0.500 3.210 5.213
0.006 0.154 0.848 1.610
Fig. 5 shows the magnetic hysteresis loops of the LBFO– BYIG composites with different BYIG concentrations. It shows obviously enhanced ferromagnetic properties and the magnetic properties are strongly dependent on the amount of BYIG. It indicates that the saturation magnetization (Ms) and the remnant magnetization (Mr) both increase with increasing BYIG concentration [15]. It can be seen from Table 1 that the values of Ms and Mr of the composite powders increase while the Hc value of the composite powders decrease with increasing BYIG concentration. This phenomenon is due to the fact that the BYIG is a classical soft magnetic ferrite while the BFO is of antiferromagnetic nature [16]. Fig. 5. Magnetic hysteresis loops of the xLBFO–(1 x)BYIG composite powders calcined at 800 1C with different BYIG concentrations.
indicating that related elements are distributed uniformly, implying that the two phases are well dispersed in the composite powders [9].
4. Conclusions The LBFO–BYIG composite powders were prepared by a onestep sol–gel method. The LBFO and BYIG phase can coexist in
M. Liu et al. / Ceramics International 40 (2014) 6301–6305
the composite powders without any secondary phase. Compared with the conventional physical mixing method, the process of one-step sol–gel method is much simpler and the obtained composite powders are very homogeneous. Magnetic hysteresis loops of the LBFO–BYIG composite powders indicate that the introduction of BYIG could significantly increase the magnetization of LBFO. Acknowledgments This work is supported by the Science and Technology Foundation of Shaanxi Province (Grant no. 2013KJXX-79) and the Scientific Research Starting Foundation of Shaanxi University of Science and Technology (Grant no. BJ11-03). References [1] H. Schmid, Multi-ferroic magnetoelectrics, Ferroelectrics 162 (1994) 317–318. [2] Z.H. Dai, Y. Akishige, Electrical properties of BiFeO3–BaTiO3 ceramics fabricated by mechanochemical synthesis and spark plasma sintering, Materials Letters 88 (2012) 36–39. [3] Y. Lin, H.B. Yang, Z.F. Zhu, F. Wang, La0.1Bi0.9FeO3–BiY2Fe5O12 composites with simultaneously improved magnetization and polarization, Ceramics International 39 (2013) 4679–4682. [4] S.Y. Wang, S. Qiu, J. Gao, Y. Feng, W.N. Su, Electrical reliability and leakage mechanisms in highly resistive multiferroic La0.1Bi0.9FeO3 ceramics, Applied Physics Letters 98 (2011) 152902. [5] F. Yan, S. Miao, I. Sterianou, I.M. Reaney, M.O. Lai, L. Lu, W.D. Song, Multiferroic properties and temperature-dependent leakage mechanism of Sc-substituted bismuth ferrite–lead titanate thin films, Scripta Materialia 64 (2011) 458–461. [6] Z.G. Wang, Y.D. Yang, R. Viswan, J.F. Li, D. Viehland, Giant electric field controlled magnetic anisotropy in epitaxial BiFeO3–CoFe2O4 thin film heterostructures on single crystal Pb(Mg1/3Nb2/3)0.7Ti0.3O3 substrate, Applied Physics Letters 99 (2011) 043110.
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[7] T.T. Carvalho, J.R.A. Fernandes, J. Cruze, J.V. Vidal, N.A. Sobolev, F. Figueiras, S. Das, V.S. Amaral, A. Almeida, J.A. Moreira, P.B. Tavares, Room temperature structure and multiferroic properties in Bi0.7La0.3FeO3 ceramics, Journal of Alloys and Compounds 554 (2013) 97–103. [8] X.H. Liu, Z. Xu, X.Y. Wei, Z. Dai, X. Yao, Ferroelectric, ferromagnetic, and magnetoelectric characteristics of 0.9(0.7BiFeO3–0.3BaTiO3)– 0.1CoFe2O4 ceramic composite, Journal of the American Ceramic Society 93 (2010) 2975–2977. [9] Y. Lin, H.B. Yang, Z.F. Zhu, Impedance spectroscopy analysis of 0.7BiFeO3–0.3BaTiO3/BiY2Fe5O12 composites with simultaneously improved magnetization and remnant polarization, Materials Chemistry and Physics 136 (2012) 286–291. [10] H.B. Yang, Q.Q. Ke, H.Y. Si, J.S. Chen, 0.7BiFeO3–0.3BaTiO3– Y3Fe5O12 composites with simultaneously improved electrical and magnetic properties, Journal of Applied Physics 111 (2012) 024104. [11] C.L. Fei, Y. Zhang, Z. Yang, Y. Liu, R. Xiong, J. Shi, X.F. Ruan, Synthesis and magnetic properties of hard magnetic (CoFe2O4)–soft magnetic (Fe3O4) nano-composite ceramics by SPS technology, Journal of Magnetism and Magnetic Materials 323 (2011) 1811–1866. [12] D. Roy, C. Shivakumara, P.S.A. Kumar, Observation of the exchange spring behavior in hard–soft-ferrite nanocomposite, Journal of Magnetism and Magnetic Materials 321 (2009) L11–L14. [13] W. Cai, C.L. Fu, W.G. Hu, G. Chen, X.L. Deng, Effects of microwave sintering power on microstructure, dielectric, ferroelectric and magnetic properties of bismuth ferrite ceramics, Journal of Alloys and Compounds 554 (2013) 64–71. [14] A. Srinivas, T. Karthik, R. Gopalan, V. Chandrasekaran, Improved magnetoelectricity by uniaxial magnetic field pressed and sintered composites in BaTiO3(x)–BaFe12O19(1 x) system (x¼ 0.8, 0.6), Materials Science and Engineering B 172 (2010) 289–293. [15] W. Zhang, C. Gao, R. Ji, C.X. Fang, Y.W. Zeng, Low-temperature synthesis and microstructure–property study of single-phase yttrium iron garnet (YIG) nanocrystals via a rapid chemical coprecipitation, Materials Chemistry and Physics 125 (2011) 646–651. [16] H.J. Zhao, J. Zhou, B. Li, Z.L. Gui, L.T. Li, Microstructure and densification mechanism of low temperature sintering Bi-substituted yttrium iron garnet, Journal of Electroceramics 21 (2008) 802–804.
CERAMICS INTERNATIONAL
Ceramics International 40 (2014) 6301–6305 www.elsevier.com/locate/ceramint
Short communication
A simple method of synthesizing homogeneous La0.1Bi0.9FeO3–BiY2Fe5O12 composite powders Miao Liu, Haibo Yangn, Ying Lin, Yanyan Yang School of Materials Science and Engineering, Shaanxi University of Science and Technology, Xi'an 710021, China Received 9 September 2013; received in revised form 24 September 2013; accepted 24 September 2013 Available online 2 October 2013
Abstract La0.1Bi0.9FeO3–BiY2Fe5O12 (abbreviated as LBFO–BYIG) composites were synthesized via a one-step sol–gel method. The synthesized composite powders were characterized using X-ray diffraction and scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy. The magnetic properties of the as-prepared composite powders were investigated by a vibrating sample magnetometer. The asprepared LBFO–BYIG composite powders show a good homogeneity of the two phases and a good crystallinity. Additionally, the magnetization of LBFO can be improved by the introduction of proper amount of BYIG. & 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: B. Composites; C. Magnetic properties; Homogeneity
1. Introduction Multiferroic materials with coexistence of two or more ferroic order parameters (ferroelectric, ferromagnetic or ferroelastic) have drawn increasing interest due to their potential applications as multifunctional devices such as multiple state memory elements, sensors, actuators and transducers [1]. However, very few mutiferroic materials exist in nature or have been synthesized in the laboratory [2]. More recently, the surge in interest has been further stimulated by the unique room-temperature single-phase multiferroic BiFeO3 (BFO) with high Curie (Tc ¼ 1103 K) and Neel (TN ¼ 643 K) temperatures [3]. But the practical applications of BFO materials have been hindered because of their large leakage current (RT) and weak magnetic behavior as a result of the small amounts of Fe2 þ and oxygen vacancies and their spiral modulated spin structure, respectively [4,5]. Recently, many methods have been employed to improve the magnetization by forming constrained epitaxial films and chemical substitution. For example, Wang et al. have reported the preparation of the BiFeO3–CoFe2O4 composite epitaxial thin films using pulsed laser deposition method [6]. Carvalho et al. have reported the n
Corresponding author. Tel./fax: þ 86 29 86168688. E-mail address: [email protected] (H. Yang).
preparation of the Bi0.7La0.3FeO3 ceramics by a sol–gel method [7]. But the enhancement is limited because they can only suppress or destroy the spin cycloid but cannot change the intrinsic antiferromagnetic nature of BFO-based single-phase materials. An alternative effective way of enhancing the magnetism for the BFO-based multiferroics is to introduce suitable ferrites to form composites [8]. Liu et al. have reported the preparation of CoFe2O4 and 0.7BiFeO3–0.3BaTiO3 separately, where CoFe2O4 was synthesized by a combustion method and 0.7BiFeO3–0.3BaTiO3 by a traditional solid-state method. After preparation of CoFe2O4 and 0.7BiFeO3– 0.3BaTiO3, they were mixed by ball-milling and sintered at 1010 1C for 2 h [8]. However, the electrical properties would deteriorate owing to the low resistivity of CoFe2O4. Y3Fe5O12 (YIG) is known to be a classical microwave ferrite and possesses high magnetization and resistivity. Its sintering temperature can be lowered from 1400 1C to 1000 1C by the substitution of Y3 þ by Bi3 þ to form BiY2Fe5O12. Our group has introduced Y3Fe5O12 and BiY2Fe5O12 into 0.7BiFeO3– 0.3BaTiO3 to form composite to simultaneously enhance the magnetic and ferroelectric properties of 0.7BiFeO3–0.3BaTiO3 due to the high magnetization and resistivity of YIG and BYIG [9,10]. Generally, the strategy to prepare the composite powders is synthesizing single-phase powder individually and then mixing them together by ball milling, which is called
0272-8842/$ - see front matter & 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved. http://dx.doi.org/10.1016/j.ceramint.2013.09.108
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the physical mixing method [11,12]. It is well known that the homogeneity of the composite powders prepared by the physical mixing method is limited. Consequently, the aim of this paper is to synthesize homogeneous LBFO/BYIG composite powders via a one-step sol–gel method. The LBFO/BYIG composite powders were synthesized by calcining the sol containing the starting materials of both LBFO and BYIG at different mass ratios. 2. Experimental procedure To prepare xLBFO–(1 x)BYIG composites (with x=0.9, 0.8, 0.7, and 0.6) using the one-step sol–gel method, reagents of Bi(NO3)3, Fe(NO3)3 9H2O, Y(NO3)3 6H2O, La(NO3)3 6H2O and C6H8O7 H2O were used as starting materials. An aqueous solution of C6H8O7 H2O was prepared in distilled water. Then stoichiometric amounts of Bi(NO3)3, Fe(NO3)3 9H2O, Y(NO3)3 6H2O, and La(NO3)3 6H2O were added into the solution stirred at 80 1C. In order to avoid precipitation and get a homogenous mixture solution, some C2H8N2 was added into the above solution at the same time. After that the reaction solution mixture was dried at 200 1C for 2 h. Black color floppy carbonaceous material was formed after drying, which was called precursor powder. Then the precursor powders were calcined in air to obtain xLBFO–(1 x)BYIG composite powders. The phase composition of LBFO–BYIG composite powders was detected by a X-ray diffractometer (XRD) with Cu Kα radiation (Rigaku D/MAX-2400, Japan). The morphology of the composite powders was analyzed using a scanning electron microscope (SEM; Hitachi S-4800, Japan) equipped with energy-dispersive X-ray spectroscopy (EDS). The magnetic hysteresis loops of the composite powders were measured by a vibrating sample magnetometer 113 (VSM) (Lake Shore 7410, USA). 3. Results and discussion The XRD patterns of the 0.6LBFO–0.4BYIG composite powders with different calcining temperatures ranging from 600 to 800 1C for 4 h are shown in Fig. 1(a). After being heated at 600 1C in air for 4 h, the main diffraction peaks of LBFO and BYIG can be found while the intensities of diffraction peaks are weak indicating that the crystallinity of powder is not good. Although major peaks due to LBFO and BYIG are obviously enhanced for the powders calcined at 700 1C, additional peaks indexed to Fe2O3 are also observed indicating that the formation process of LBFO and BYIG is not complete. With the increase in temperature from 700 to 800 1C, the diffraction peaks from Fe2O3 almost disappear completely and pure phase LBFO and BYIG can be obtained. It indicates that the two phases can co-exist in the synthesized composite powders at 800 1C. The XRD patterns are in excellent correspondence with JCPDS 20-1069 of LBFO and JCPDS 43-0507 of BYIG. All the diffraction peaks can be perfectly indexed to the rhombohedral distorted perovskite structure of LBFO and the cubic structure of YIG.
Fig. 1. (a) XRD patterns of the 0.6LBFO–0.4BYIG composites with different calcining temperatures; (b) XRD patterns of the LBFO–BYIG composites with different LBFO concentrations.
The XRD patterns of the LBFO–BYIG composite powders calcined at 800 1C for 4 h with different BYIG concentrations are shown in Fig. 1(b). It can be clearly seen that only the parent phases of LBFO and BYIG can be found in all the samples. Moreover, the XRD shows that the synthesized powders of LBFO and BYIG have pure rhombohedral distortion perovskite structure and cubic structure, respectively [13]. Within the resolution limit of XRD any other immediate phase cannot be detected. The above powder X-ray diffractograms reveal that LBFO and BYIG phases co-exist after being calcined at 800 1C with a high crystallinity and without any impurity phases. Obviously, by increasing the BYIG concentration, the diffraction peaks of BYIG become strengthened gradually. Fig. 2 shows the morphology of the 0.6LBFO–0.4BYIG composite powders calcined at different temperatures ranging from 600 1C to 800 1C for 4 h. It can be seen that in Fig. 2(a) grains are not well developed. Moreover, the powders are inhomogeneous
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Fig. 2. SEM micrographs of the 0.6LBFO–0.4BYIG composite powders calcined at different temperatures: (a) 600 1C, (b) 700 1C, and (c) 800 1C.
Fig. 3. SEM micrographs of the xLBFO–(1 x)BYIG composite powders calcined at 800 1C: (a) x¼ 0.9, (b) x¼ 0.8, (c) x ¼0.7, and (d) x ¼0.6.
and seriously aggregated. With increasing calcining temperature, the composite powders become more and more homogeneous and all the grains are developed better and better, especially those in Fig. 2(c). The morphology of the xLBFO–(1 x)BYIG composite powders calcined at 800 1C for 4 h is shown in Fig. 3. Because the formation temperature of BYIG is higher than that of LBFO [9,14], the small grains (Spot A) are of the BYIG
phase while the large grains (Spot B) are of the LBFO phase. With increasing BYIG concentration, LBFO and BYIG powders become more and more homogeneous and the grains develop better and better. This phenomenon is also consistent with the XRD results. Fig. 4 shows the EDS mapping analysis result of the representative 0.8LBFO–0.2BYIG composite powders. It can be easily found that four different kinds of colors are uniform,
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Fig. 4. EDS mapping analysis result of the 0.8LBFO–0.2BYIG composite powders.
Table 1 Magnetic parameters of the xLBFO–(1 x)BYIG composite powders calcined at 800 1C. x
Hc (G)
Ms (emu/g)
Mr (emu/g)
0.9 0.8 0.7 0.6
3779.81 132.47 67.18 59.96
0.175 0.500 3.210 5.213
0.006 0.154 0.848 1.610
Fig. 5 shows the magnetic hysteresis loops of the LBFO– BYIG composites with different BYIG concentrations. It shows obviously enhanced ferromagnetic properties and the magnetic properties are strongly dependent on the amount of BYIG. It indicates that the saturation magnetization (Ms) and the remnant magnetization (Mr) both increase with increasing BYIG concentration [15]. It can be seen from Table 1 that the values of Ms and Mr of the composite powders increase while the Hc value of the composite powders decrease with increasing BYIG concentration. This phenomenon is due to the fact that the BYIG is a classical soft magnetic ferrite while the BFO is of antiferromagnetic nature [16]. Fig. 5. Magnetic hysteresis loops of the xLBFO–(1 x)BYIG composite powders calcined at 800 1C with different BYIG concentrations.
indicating that related elements are distributed uniformly, implying that the two phases are well dispersed in the composite powders [9].
4. Conclusions The LBFO–BYIG composite powders were prepared by a onestep sol–gel method. The LBFO and BYIG phase can coexist in
M. Liu et al. / Ceramics International 40 (2014) 6301–6305
the composite powders without any secondary phase. Compared with the conventional physical mixing method, the process of one-step sol–gel method is much simpler and the obtained composite powders are very homogeneous. Magnetic hysteresis loops of the LBFO–BYIG composite powders indicate that the introduction of BYIG could significantly increase the magnetization of LBFO. Acknowledgments This work is supported by the Science and Technology Foundation of Shaanxi Province (Grant no. 2013KJXX-79) and the Scientific Research Starting Foundation of Shaanxi University of Science and Technology (Grant no. BJ11-03). References [1] H. Schmid, Multi-ferroic magnetoelectrics, Ferroelectrics 162 (1994) 317–318. [2] Z.H. Dai, Y. Akishige, Electrical properties of BiFeO3–BaTiO3 ceramics fabricated by mechanochemical synthesis and spark plasma sintering, Materials Letters 88 (2012) 36–39. [3] Y. Lin, H.B. Yang, Z.F. Zhu, F. Wang, La0.1Bi0.9FeO3–BiY2Fe5O12 composites with simultaneously improved magnetization and polarization, Ceramics International 39 (2013) 4679–4682. [4] S.Y. Wang, S. Qiu, J. Gao, Y. Feng, W.N. Su, Electrical reliability and leakage mechanisms in highly resistive multiferroic La0.1Bi0.9FeO3 ceramics, Applied Physics Letters 98 (2011) 152902. [5] F. Yan, S. Miao, I. Sterianou, I.M. Reaney, M.O. Lai, L. Lu, W.D. Song, Multiferroic properties and temperature-dependent leakage mechanism of Sc-substituted bismuth ferrite–lead titanate thin films, Scripta Materialia 64 (2011) 458–461. [6] Z.G. Wang, Y.D. Yang, R. Viswan, J.F. Li, D. Viehland, Giant electric field controlled magnetic anisotropy in epitaxial BiFeO3–CoFe2O4 thin film heterostructures on single crystal Pb(Mg1/3Nb2/3)0.7Ti0.3O3 substrate, Applied Physics Letters 99 (2011) 043110.
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