• Journal of Magnetics
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• 제16권1호
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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.

• 한국재료학회지
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• 제22권12호
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• pp.675-681
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• 2012

We aimed to examine the co-doping effects of 1/6 mol% $Mn_3O_4$ and 1/4 mol% $Cr_2O_3$ (Mn:Cr = 1:1) on the reaction, microstructure, and electrical properties, such as the bulk defects and grain boundary properties, of ZnO-$Bi_2O_3-Sb_2O_3$ (ZBS; Sb/Bi = 0.5, 1.0, and 2.0) varistors. The sintering and electrical properties of Mn,Cr-doped ZBS, ZBS(MnCr) varistors were controlled using the Sb/Bi ratio. Pyrochlore ($Zn_2Bi_3Sb_3O_{14}$), ${\alpha}$-spinel ($Zn_7Sb_2O_{12}$), and ${\delta}-Bi_2O_3$ (also ${\beta}-Bi_2O_3$ at Sb/Bi ${\leq}$ 1.0) were detected for all of the systems. Mn and Cr are involved in the development of each phase. Pyrochlore was decomposed and promoted densification at lower temperature on heating in Sb/Bi = 1.0 system by Mn rather than Cr doping. A more homogeneous microstructure was obtained in all systems affected by ${\alpha}$-spinel. In ZBS(MnCr), the varistor characteristics were improved dramatically (non-linear coefficient, ${\alpha}$ = 40~78), and seemed to form ${V_o}^{\cdot}$(0.33 eV) as a dominant defect. From impedance and modulus spectroscopy, the grain boundaries can be seen to have divided into two types, i.e. one is tentatively assigned to ZnO/$Bi_2O_3$ (Mn,Cr)/ZnO (0.64~1.1 eV) and the other is assigned to the ZnO/ZnO (1.0~1.3 eV) homojunction.

• Journal of Magnetics
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• 제14권1호
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• pp.1-6
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• 2009

The magnetic properties of ${Bi_x}{Ca_{1-x}}{MnO_3}$ for x = 0.12, 0.13, 0.14, 0.15, and 0.16 were examined by measuring magnetic susceptibility, resistivity and electron magnetic resonance at different temperatures. ${Bi_x}{Ca_{1-x}}{MnO_3}$ showed complicated magnetic structure that varies with temperature and composition, particularly around Bi composition x. 0.15. The aim of this study was to determine how the magnetic and physical properties of ${Bi_x}{Ca_{1-x}}{MnO_3}$ change in this region. In addition, first principles calculations of the magnetic phase of ${Bi_x}{Ca_{1-x}}{MnO_3}$ for x = 0, 0.125, 0.25 were carried out, and the spin state, electric and magnetic characteristics are discussed.

• Journal of Magnetics
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• 제21권2호
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• pp.168-172
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• 2016

$BiMnO_3$ has been a promising candidate as a magnetoelectric multiferroic while there have been many controversial reports on its ferroelectricity. The detailed analysis of its film growth, especially the growth of thin film having monoclinic symmetry has not been reported. We studied the effect of miscut angle, the substrate surface, and film thickness on the symmetry of $BiMnO_3$ thin film. A flat $SrTiO_3$ (110) substrate resulted in a thin film with three domains of $BiMnO_3$ and 1 degree miscut in the $SrTiO_3$ (110) substrate resulted in dominant domain preference in the $BiMnO_3$ thin film. The larger miscut resulted in a nearly perfect detwinned $BiMnO_3$ film with a monoclinic phase. This strong power of domain selection due to the step edge of the substrate was efficient even for the thicker film which showed a rather relaxed growth behavior along the $SrTiO_3$ [1-10] direction.

• 한국세라믹학회지
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• 제34권2호
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• pp.123-130
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• 1997

본 연구에서는 유전상수가 크고, 유전체 손실이 적으며, 사용온도 범위에서 정전용량 변화율(TCC : tem-perature coefficient of capacitance)이 작고, 고압에 견딜 수 있는 재료를 개발하기 위하여 중고압용 capacitance의 기본재료로써 (Sr.Pb.Ca)TiO3-xBi2O3.3TiO2 계에서 Bi2O3.3TiO2의 mol.%를 5, 6, 7, 8, 9 mol.%로 변화시켰으며, 그 결과 고용한계 함량이 6mol.%이며, 6mol.%이상에서는 침상구조의 증가에 기인하여 유전율이 다시 감소하는 경향을 보였다. dopant로써 SiO2, Nb2O3, MnO2를 선정하여 첨가한 결과, MnO2를 첨가한 것이 유전성질이 가장 우수하였으며, MnO2의 함량이 0, 0.15, 0.3, 0.45 wt.% 증가함에 따라서 유전율의 감소와 동시에, TOC특성의 급격한 향상을 가져왔다.

• 한국세라믹학회지
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• 제29권2호
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• pp.161-165
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• 1992

Nonlinear exponents and electron trap density variations were observered in ZnO-Bi2O3-MnO2 ternary ZnO varistors as a function of heat treatment temperature. Three kinds of ZnO varistor compositions were selected; i.e. 99.0 ZnO-0.5 Bi2O3-0.5 MnO2, 98.5 ZnO-1.0 Bi2O3-0.5 MnO2, and 98.0 ZnO-1.5 Bi2O3-0.5 MnO2 in mol%. Sintering was done at 1150$^{\circ}C$ for three hours, and heat treatments were done at 500$^{\circ}C$, 700$^{\circ}C$, and 900$^{\circ}C$. When heat treated at 500$^{\circ}C$, nonlinear exponents were increased regardless of the Bi2O3 amount. Increasing heat treatment temperature above 500$^{\circ}C$ resulted in lowering nonlinear exponents. Nonlinear exponents seem to be related to the 0.17 and 0.33 eV electron traps which are possibly of intrinsic origin.

• 한국전기전자재료학회논문지
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• 제25권11호
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• pp.878-885
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• 2012

In this study we aims to examine the co-doping effects of 1/3 mol% $Mn_3O_4+Co_3O_4$ (1:1) on the reaction, microstructure, and electrical properties such as the bulk defects and grain boundary properties of $ZnO-Bi_2O_3-Sb_2O_3$ (ZBS; Sb/Bi=0.5, 1.0, and 2.0) varistors. The sintering and electrical properties of Mn,Co-doped ZBS, ZBS(MCo) varistors were controlled by Sb/Bi ratio. Pyrochlore ($Zn_2Bi_3Sb_3O_{14}$) was decomposed and promoted densification at lower temperature on heating in Sb/Bi=1.0 by Mn rather than Co. Pyrochlore on cooling was reproduced in all systems however, spinel (${\alpha}$- or ${\beta}$-polymorph) did not formed in Sb/Bi=0.5. More homogeneous microstructure was obtained in $Sb/Bi{\geq}1.0$ In ZBS(MCo), the varistor characteristics were improved drastically (non-linear coefficient, ${\alpha}$=30~49), and seemed to form $Zn_i^{..}$(0.17 eV) and $V_o^{\bullet}$(0.33 eV) as dominant defects. From impedance and modulus spectroscopy (IS & MS), the grain boundaries have divided into two types, i.e. the one is tentatively assign to $ZnO/Bi_2O_3(Mn,Co)/ZnO$ (0.47 eV) and the other ZnO/ZnO (0.80~0.89 eV) homojunctions.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2002년도 춘계 학술발표강연 및 논문개요집
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• pp.129-129
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• 2002

• 한국재료학회지
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• 제2권1호
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• pp.12-18
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• 1992

등온용량과도분광법(Isothermal Capacitance Transient spectroscopy)을 이용하여 ZnO 바리스터의 포획준위를 결정하였다. 여기서 등온용량과도분광기는 YHP 4192A 임피던스 Analyzer와 데이터해석을 위한 개인용 컴퓨터로 구성된다. 이 실험에서 우리는 $ZnO-Bi_2O_3$에 MnO 및 CoO를 첨가한계에서 $-40^{\circ}C~60^{\circ}C$ 온도범위에서 0.28, 0.48, 0.50, 0.94eV 등의 입계포획준위가 존재함을 볼 수 있었다. 또한, $ZnO-Bi_2O_3$계는 CoO를 첨가하면 hole에 의한 emission특성을 나타내고, MnO를 첨가하면 전자에 의한 emission특성을 나타냄을 알 수 있었다. 그리고 비 직선저항계수 $\alpha$는 도너농도의 감소에 직접적으로 비례하였으나, 포획준위의 밀도와는 별다른 비례관계를 발견할 수 없었다. 결론적으로 $ZnO-Bi_2O_3-MnO$계에 CoO를 첨가함에 따라 $\alpha$값이 증가하는 한편, 포획준위밀도는 CoO의 첨가로 감소함을 알 수 있었다.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2002년도 춘계 학술발표강연 및 논문개요집
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• pp.53-53
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• 2002