• Title, Summary, Keyword: $BiFeO_3$

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Effects of Mn Doping on Structural and Magnetic Properties of Multiferroic BiFeO3 Nanograins Made by Sol-gel Method

  • Raghavender, A.T.;Hong, Nguyen Hoa
    • Journal of Magnetics
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    • v.16 no.1
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    • pp.19-22
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    • 2011
  • [ $BiFeO_3$ ]is a multiferroic material that attracts attentions of many research groups due to its potential as being ferroelectric and ferromagnetic above room temperature. We have prepared both undoped- and Mn-doped $BiFeO_3$ by sol-gel auto-ignition method. Doping of Mn has resulted in decreasing grain size from 60 to 32 nm. X-ray diffraction data show that the samples are pure and single-phase. Infrared measurements on $BiFeO_3$ and Mn-doped $BiFeO_3$ revealed intrinsic stretching vibrations of tetrahedral sites of $Fe^{3+}$-O and of octahedral $Bi^{3+}$-O as well. On the other hand, as the Mn concentration increases, the magnetic moment of $BiFeO_3$ increases. It gives some suggestions in manipulating structural and magnetic properties of $BiFeO_3$ by doping Mn.

Mössbauer Studied of Multiferroic Bi2/3La1/3FeO3 Nanoparticles (Multiferroic Bi2/3La1/3FeO3 나노입자의 Mössbauer 연구)

  • Lee, Seung-Wha
    • Journal of the Korean Magnetics Society
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    • v.16 no.1
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    • pp.28-33
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    • 2006
  • La substituted perovskite $BiFeO_3$ have been prepared by a sol-gel method. Magnetic and structural properties of the powders were characterized with Mossbauer spectroscopy, XRD, SEM, and TG-DTA. The crystal structure is found to be a rhombohedrally distorted perovskite structure with the lattice constant $\alpha=3.985{\AA}\;and\;\alpha=89.5^{\circ}.\;Bi_{2/3}La_{1/3}FeO_3$ powders that were annealed at and above $600^{\circ}C$ have a single-phase perovskite structure. However, powders annealed at $900^{\circ}C$ have a typical perovskite structure with small amount of $Bi_2O_3$ phase. The Neel temperature of $Bi_{2/3}La_{1/3}FeO_3$ is found to be $680\pm3K$. The isomer shift value at room temperature is found to be 0.27 mm/s relative to the Fe metal, which is consistent with high-spin $Fe^{3+}$ charge states. Debye temperature far$Bi_{2/3}La_{1/3}FeO_3$ is found to be $305\pm5K$. The average hyperfine field $H_{hf}(T)$ of the $Bi_{2/3}La_{1/3}FeO_3$, shows a temperature dependence of $[H_{hf}(T)-H_{hf}(0)]/H_{hf}(0)=-0.42(T/T_N)^{3/2}-0.13(T/T_N)^{5/2}$ for $T/T_N<0.7$ indicative of spin-wave excitation.

Preparation and properties of multiferroic bismuth iron oxides

  • Nam, Joong-Hee;Joo, Yong-Hui;Cho, Jeong-Ho;Chun, Myoung-Pyo;Kim, Byung-Ik
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.19 no.2
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    • pp.66-69
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    • 2009
  • The compositional dependence of bismuth iron oxides and effect of La-substitutions in the structure of $BiFeO_3$ compounds were investigated, which compounds were synthesized by conventional ceramic processing. It is shown that some of bismuth iron oxides including $BiFeO_3$ show the narrow single phase region. The effect of La-doping in $BiFeO_3$ was presented as disappearance of many impurity phases of Bi-Fe-O compounds. The lower electrical resistivity was obtained as those compositions of Fe deficient region and La-doped $BiFeO_3$. The saturation magnetization of La-doped $BiFeO_3$ was increased with La content. The dielectric dispersion was also observed for those Bi-Fe-O compounds with Fe deficient and La-doped $BiFeO_3$ at low frequencies under 1 kHz.

Crystal Structure and Microstructure Variation of Nonstoichiometric Bi1±xFeO3±δ and Ti-doped BiFeO3 Ceramics under Various Sintering Conditions (비화학양론적 Bi1±xFeO3±δ와 Ti가 첨가된 BiFeO3의 소결조건에 따른 결정구조와 미세구조 변화)

  • Bae, Jihee;Kim, Jun Chan;Kim, Myong-Ho;Lee, Soonil
    • Korean Journal of Materials Research
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    • v.30 no.2
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    • pp.61-67
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    • 2020
  • BiFeO3 with perovskite structure is a well-known material that has both ferroelectric and antiferromagnetic properties called multiferroics. However, leaky electrical properties and difficulty of controlling stoichiometry due to Bi volatility and difficulty of obtaining high relative density due to high dependency on the ceramic process are issues for BiFeO3 applications. In this work we investigated the sintering behavior of samples with different stoichiometries and sintering conditions. To understand the optimum sintering conditions, nonstoichiometric Bi1±xFeO3±δ ceramics and Ti-doped Bi1.03Fe1-4x/3TixO3 ceramics were synthesized by a conventional solid-state route. Dense single phase BiFeO3 ceramics were successfully fabricated using a two-step sintering and quenching process. The effects of Bi volatility on microstructure were determined by Bi-excess and Ti doping. Bi-excess increased grain size, and Ti doping increased sintering temperature and decreased grain size. It should be noted that Ti-doping suppressed Bi volatility and stabilized the BiFeO3 phase.

Formation of Layered Bi5Ti3FeO15 Perovskite in Bi2O3-TiO2-Fe2O3 Containing System

  • Borse, Pramod H.;Yoon, Sang-Su;Jang, Jum-Suk;Lee, Jae-Sung;Hong, Tae-Eun;Jeong, Euh-Duck;Won, Mi-Sook;Jung, Ok-Sang;Shim, Yoon-Bo;Kim, Hyun-Gyu
    • Bulletin of the Korean Chemical Society
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    • v.30 no.12
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    • pp.3011-3015
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    • 2009
  • Structural and thermo-analytical studies were carried out to understand the phase formation kinetics of the single phase $Bi_5Ti_3FeO_{15}$ (BTFO) nanocrystals in $Bi_2O_3-Fe_2O_3-TiO_2$, during the polymerized complex (PC) synthesis method. The crystallization of Aurivillius phase $Bi_5Ti_3FeO_{15}$ layered perovskite was found to be initiated and achieved under the temperature conditions in the range of ${\sim}$800 to 1050$^{\circ}C$. The activation energy for grain growth of $Bi_5Ti_3FeO_{15}$ nanocrystals (NCs) was very low in case of NCs formed by PC (2.61 kJ/mol) than that formed by the solid state reaction (SSR) method (10.9 kJ/mol). The energy involved in the phase transformation of Aurivillius phase $Bi_5Ti_3FeO_{15}$ from $Bi_2O_3-Fe_2O_3-TiO_2$ system was ${\sim}$ 69.8 kJ/mol. The formation kinetics study of $Bi_5Ti_3FeO_{15}$ synthesized by SSR and PC methods would not only render a large impact in the nanocrystalline material development but also in achieving highly efficient visible photocatalysts.

Fabrication and Characterization of (1-x)BiFeO3-xBaTiO3 Ceramics Prepared by a Solid State Reaction Method

  • Chandarak, S.;Unruan, M.;Sareein, T.;Ngamjarurojana, A.;Maensiri, S.;Laoratanakul, P.;Ananta, S.;Yimnirun, R.
    • Journal of Magnetics
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    • v.14 no.3
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    • pp.120-123
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    • 2009
  • In this study, BiFe$O_3$-BaTi$O_3$ ceramics have been fabricated by a solid-state reaction method. The effects of BaTi$O_3$ content in the (1-x)BiFe$O_3$-xBaTi$O_3$ (x = 0.1, 0.2, 0.25, 0.3, 0.4, 0.5) system on crystal structure and magnetic, dielectric, and ferroelectric properties were investigated. Perovskite BiFe$O_3$ was stabilized through the formation of a solid solution with BaTi$O_3$. Rhombohedrally distorted structure (1-x)BiFe$O_3$-xBaTi$O_3$ ceramics showed strong ferromagnetism at x = 0.5. Dielectric and ferroelectric properties of the BiFe$O_3$-BaTi$O_3$ system also changed significantly upon addition of BaTi$O_3$. It was found that the maximum dielectric and ferroelectric properties were exhibited in the (1-x)BiFe$O_3$-xBaTi$O_3$ system at x = 0.25. This suggested the morphotropic phase boundary (MPB) with the coexistence of both rhombohedral and cubic phases of the (1-x)BiFe$O_3$-xBaTi$O_3$ system at x = 0.25.

Dielectric and Magnetic Properties of Niobium and Cobalt Co-substituted Multiferroic BiFeO3 Thin Films (Niobium과 Cobalt를 첨가한 Multiferroic BiFeO3 박막의 유전 특성 및 자성 특성)

  • Jun, Youn-Ki;Hong, Seong-Hyeon
    • Journal of the Korean Ceramic Society
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    • v.45 no.9
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    • pp.556-560
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    • 2008
  • The effects of Nb and Co ion substitution on the dielectric and magnetic properties of the multiferroic $BiFeO_3$ thin films have been investigated. Heteroepitaxial $BiFeO_3$ thin films were deposited by Pulsed Laser Deposition method. Nb substitution decreased the leakage current by 6 orders of magnitude and Co substituted $BiFeO_3$ thin films showed an enhanced magnetization, 2 times larger than that of un-substituted $BiFeO_3$. Through the co-substitution of Co and Nb, $BiFeO_3$ thin films with a low leakage current and an enhanced magnetization could be obtained.

Simultaneously Enhanced Magnetic and Ferroelectric Properties of $Bi_{0.9}Dy_{0.1}Fe_{0.97}Co_{0.03}O_3 $ compound

  • Yu, Yeong-Jun;Hwang, Ji-Seop;Park, Jeong-Su;Lee, Ju-Yeol;Gang, Ji-Hun;Lee, Gwang-Hun;Lee, Bo-Hwa;Kim, Gi-Won;Lee, Yeong-Baek
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.147-147
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    • 2013
  • Multiferroic material $BiFeO_3$ (BFO) is a typical multiferroic material with a room-temperature magnetoelectric coupling in view of high magnetic- and ferroelectric-ordering temperatures (Neel temperature $T_N$ ~ 647 K and Curie temperature TC ~1,103 K). Rare-earth ion substitution at the Bi sites is very interesting, which induces suppressed volatility of the Bi ion and improved ferroelectric properties. At the same time, the Fe-site substitution with magnetic ions is also attracting, since the enhanced ferromagnetism was reported. In this study, BFO, $Bi_{0.9}Dy_{0.1}FeO_3$ (BDFO), $BiFe_{0.97}Co_{0.03}O_3$ (BFCO) and $Bi_{0.9}Dy_{0.1}Fe_{0.97}Co_{0.03}O_3 $ (BDFCO) compounds were prepared by conventional solid-state reaction and wet-mixing method. High-purity $Bi_2O_3$, $Dy_2O_3$, $Fe_2O_3$ and $Co_3O_4$ powders with the stoichiometric proportions were mixed, and calcined at $500^{\circ}C$ for 24 h. The samples were immediately put into an oven, which was heated up to 800oC and sintered in air for 1 h. The crystalline structure of samples was investigated at room temperature by using a Rigaku Miniflex powder diffractometer. The field-dependent magnetization measurements were performed with a vibrating-sample magnetometer. The electric polarization was measured at room temperature by using a standard ferroelectric tester (RT66B, Radiant Technologies). Dy and Co co-doping at the Bi and the Fe sites induce the enhancement of both magnetic and ferroelectric properties of $BiFeO_3$.

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Electrical Switching Effects in the Sintered $Fe_2O_3$-$Bi_2O_3$ (II) ($Fe_2O_3$-$Bi_2O_3$ 소결체의 전기적 Switching 특성(II))

  • 정환재
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.17 no.1
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    • pp.36-39
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    • 1980
  • Studies have been perfor mad on the normalization of V-I characteristics, the dependence of current runaway on the applied step voltage and the analysis of the current channet in the sintered 5Fe$_2$O$_3$-5Bi$_2$O$_3$. From the measurement of snitching Properties of the sintered 5Fe$_2$O$_3$-5Bi$_2$O$_3$, it is exe]twined that the electrical switching mechanism is that of thermal ionic breakolown.

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