• Journal of Electrochemical Science and Technology
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• 제10권4호
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• pp.424-432
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• 2019

Planar BiVO₄ and 3 wt% Mo-doped BiVO₄ (abbreviated as Mo:BiVO₄) film were prepared by the facile spin-coating method on fluorine doped SnO₂(FTO) substrate in the same precursor solution including the Mo precursor in Mo:BiVO₄ film. After annealing at a high temperature of 450℃ for 30 min to improve crystallinity, the films exhibited the monoclinic crystalline phase and nanoporous architecture. Both films showed no remarkably discrepancy in crystalline or morphological properties. To investigate the effect of surface passivation exploring the Al₂O₃ layer, the ultra-thin Al₂O₃ layer with a thickness of approximately 2 nm was deposited on BiVO₄ film using the atomic layer deposition (ALD) method. No distinct morphological modification was observed for all prepared BiVO₄ and Mo:BiVO₄ films. Only slightly reduced nanopores were observed. Although both samples showed some reduction of light absorption in the visible wavelength after coating of Al₂O₃ layer, the Al₂O₃ coated BiVO₄ (Al₂O₃/BiVO₄) film exhibited enhanced photoelectrochemical performance in 0.5 M Na₂SO₄ solution (pH 6.5), having higher photocurrent density (0.91 mA/㎠ at 1.23 V vs. reversible hydrogen electrode (RHE), briefly abbreviated as V_RHE) than BiVO₄ film (0.12 mA/㎠ at 1.23 V_RHE). Moreover, Al₂O₃ coating on the Mo:BiVO₄ film exhibited more enhanced photocurrent density (1.5 mA/㎠ at 1.23 V_RHE) than the Mo:BiVO₄ film (0.86 mA/㎠ at 1.23 V_RHE). To examine the reasons, capacitance measurement and Mott-Schottky analysis were conducted, revealing that the significant degradation of capacitance value was observed in both BiVO₄ film and Al₂O₃/Mo:BiVO₄ film, probably due to degraded capacitance by surface passivation. Furthermore, the flat-band potential (V_FB) was negatively shifted to about 200 mV while the electronic conductivities were enhanced by Al₂O₃ coating in both samples, contributing to the advancement of PEC performance by ultra-thin Al₂O₃ layer.

• 한국자기학회지
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• 제2권1호
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• pp.29-36
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• 1992

본 연구에서는 장래의 전자공업 및 정보산업의 기본소재로서 그 응용이 기대되고 있는비정질 산화물자성체를 개발하기 위한 기초연구를 수행하였다. 현재 연구보고 되어 있는 강자성비정질 산화물은 같은 조성의 다결정 ferrite에 비하여 그 자성이 빈약하므로 자성이 좀더 강한비정질 spinel ferrite의 개발이 요구된다. 자체 제작한 쌍 roller 초급내장치로써 $CaO-B_{2}O_{3}$ 계 amorphous ferrite 시료를 제조하고 얻어진 시편의 제특성을 조사하기 위해 XRD, DTA/TG, VSM, $M\"{o}ssbauer$ spectrum으로 측정한 결과 다음과 같은 결론을 얻었다. $CaO-Bi_{2}O_{3}$ 계 amorphous ferrite는 10-50 mole% CaO, 10-50 mole% $Bi_{2}O_{3}$. 40-70 mole% $Fe_{2}O_{3}$의 조성 영역에서 제조가 가능하고 $BiFeO_{3}$와 $CaFe_{4}O_{7}$의 혼합 조성부근에서 강력한 자화를 나타낸다. 특히 ${(CaO)}_{20}-{(Bi_{2}O_{3})}_{15}{(Fe_{2}O_{3}}_{65}$의 조성에 있어서는 자화가 약 21.84 emu/g(10 kOe)이며 강 자성적인 거동을 나타낸다. 이 비정질 ferrite는 반강자성상($\alpha$-상)과 강자성상($\beta$-상)으로 되어 있다. 비정질 ferrite의 결정화는 $550^{\circ}C$와 $775^{\circ}C$에서 2단계로 일어나고, 그때 나타나는 결정상은 $BiFeO_{3}$의 perovskite 상과 ${\alpha}-Fe_{2}O_{3}$ 상이다.

• 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.

• 전기학회논문지
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• 제67권4호
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• pp.543-548
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• 2018

Ferroelectric $Bi_4Ti_3O_{12}$ films were deposited on $SrTiO_3(100)$ and Si(100) substrate by using conductive $SrRuO_3$ films as underlayer, and their ferroelectric and electrical properties were investigated depending on crystal structure and orientation. C-axis oriented $Bi_4Ti_3O_{12}$ films were grown on well lattice-matched pseudo-cubic $SrRuO_3$ films deposited on $SrTiO_3(100)$ substrate, while random-oriented polycrystalline $Bi_4Ti_3O_{12}$ films were grown on $SrRuO_3$ films deposited on Si(100) substrate. The random-oriented polycrystalline film showed a good ferroelectric hysteresis property with remanent polarization ($P_r$) of $9.4{\mu}C/cm^2$ and coercive field ($E_c$) of 84.9 kV/cm, while the c-axis oriented film showed $P_r=0.64{\mu}C/cm^2$ and $E_c=47kV/cm$ in polarizaion vs electric field curve. The c-axis oriented $Bi_4Ti_3O_{12}$ film showed a dielectric constant of about 150 and lower thickness dependence in dielectric constant compared to the random-oriented film. Furthermore, the c-axis oriented $Bi_4Ti_3O_{12}$ film showed leakage current lower than that of the polycrystalline film. The difference of ferroelectric properties in two films was explained from the viewpoint of depolarization effect due to orientation of spontaneous polarization and layered crystal structure of bismuth-base ferroelectric oxide.

• 한국세라믹학회지
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• 제26권5호
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• pp.655-660
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• 1989

The physical properties and sinterabilities of ZrO2-Y2O3-Bi2O3 ternary system powder prepared by coprecipitation were investigated. The crystallization temperatures of ternary system were increased and the specific surface areas were decreased with increasing Bi2O3 amount as sintering agents both PSZ and FSZ. Especially, the partially stabilized zirconia showed monoclinic phase. The sinterability was increased with the amount of Bi2O3 added which caused liquid phase sintering.

• 한국세라믹학회지
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• 제40권7호
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• pp.672-676
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• 2003

Y$_3$Fe$_{5}$O$_{12}$(YIG), $Y_3$Fe$_{5}$O$_{12}$(Bi:YIG), TbBi:YIG를 (GdCa)$_3$(GaMgZr)$_{5}$O$_{12}$ (SGGG)기판 위에 Liquid Phase Epitaxy (LPE)법으로 단결정 후막을 성장시켰다. 기판회전속도, 과냉도, 성장시간을 고정하여 치환되는 원소의 종류와 양에 따라 가네트 단결정의 격자상수, Bi 치환양, 표면형상, 자기적 특성을 조사하였다. TbBi:YIG 조성의 경우 격자상수는 12.500 $\AA$으로 기판의 격자상수인 12.496 $\AA$에 근접하게 나타났으며, 포화자계는 150 Oe로 향상된 결과가 나타났다.

• 한국전기전자재료학회논문지
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• 제25권9호
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• pp.692-701
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• 2012

Recently, many lead-free piezoelectric materials have been investigated for the replacement of existing Pb-based piezoelectric ceramics because of globally increasing environmental interest. There has been remarkable improvement in piezoelectric properties of some lead-free ceramics such as $(Bi,Na)TiO_3-(Bi,K)TiO_3-BaTiO_3$, $(Na,K)NbO_3-LiSbO_3$, and so on. However, no one still has comparable piezoelectric properties to lead-based materials. Therefore, new lead-free piezoelectric ceramics are required. $BiFeO_3$ has a rhombohedrally distorted perovskite structure at room temperature and a very high Curie temperature ($T_C$= 1,100 K). And a very large electric polarization of 50 ~ 60 ${\mu}C/cm^2$ has been reported both in epitaxial thin film and single crystal $BiFeO_3$. Therefore, a high piezoelectric effect is expected also in a $BiFeO_3$ ceramics. The recent research activities on $BiFeO_3$ or $BiFeO_3$-based solid solutions are reviewed in this article.

• The Korean Journal of Ceramics
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• 제5권2호
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• pp.183-188
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• 1999

The crystallization behavior and electrical conductivity of the $CuO-Bi_2O_3-V_2O_5$ glasses with various CuO content were investigated. The glass formation regin was 0~20 mol% Bi2O3, 5~55 mol% CuO, and 30~90 mol% $V_2O_5$ with Tg=$275^{\circ}C$~$290^{\circ}C$. Among glasses with various compositions, the 31CuO-$14Bi_2O_3-55V_2O_5$ (mol%) glass heat-treated at $358^{\circ}C$ for 8 h showed the highest conductivity of ~ at room temperature. The heat-treated glasses increased in electrical conductivity by the order of 104 compared to non heat-treated glass. The linear relationship between 1n($\sigma$T)and $T^{-1}$ indicated that electrical conduction in the 31CuO-$14Bi_2O_3-55V_2O_5$ (mol%) glass occurred by a small polaron hopping.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 C
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• pp.1488-1490
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• 2002

The (Bi,Ba,Sr)$TiO_3$[BBST] thin films were fabricated on Pt/Ti/$SiO_2$/Si substrate by RF sputtering method. We investigated the effects of Ar/$O_2$ rates on the structural properties of BBST thin films. Decreasing the $O_2$ rates, the intensity of $BaBi_4Ti_4O_{15}$ and $Bi_4Ti_3O_{12}$ peaks were increased but the $(Ba_{0.5}Sr_{0.5})TiO_3$ peak was decreased. In the case of BBST thin films deposited with condition of 90/10 (Ar/$O_2$) ratio, the composition of Ba/Sr/Bi was 0.35/0.4/0.25. Also, in the BBST thin films deposited with condition of 80/20(Ar/$O_2$) ratio, the composition of Br,Sr and Ti were relatively uniform. But the component of Bi and Ti were diffused into the Pt layers.

• 한국자기학회지
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• 제20권6호
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• pp.222-227
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• 2010

RF 마그네트론 스퍼터링법을 이용하여 Pt/Ti/$SiO_2$/Si(100) 기판위에 $BiFeO_3$ 박막을 증착하였고, 스퍼터링 공정에서 산소량이 $BiFeO_3$ 박막에 미치는 영향을 조사하였다. $BiFeO_3$ 박막은 XRD 회절패턴의 결과를 통하여 소량의 불순물상이 존재하는 페로브스카이트 구조로 결정화되었다. $O_2$ 가스의 유량은 박막의 미세구조 및 자기적 특성에 많은 영향을 끼친다. $O_2$ 가스의 유량이 증가함에 따라 박막의 표면 거칠기 및 grain size가 증가하였다. $BiFeO_3$ 박막은 상온에서 약자성적인 거동을 보였으며, PFM 측정을 통하여 박막의 미세구조와 압전계수와의 상관관계를 조사하였다.