• Title/Summary/Keyword: Transition Metal oxides

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Anisotropy of the Electrical Conductivity of the Fayalite, Fe2SiO4, Investigated by Spin Dimer Analysis

  • Lee, Kee Hag;Lee, Jeeyoung;Dieckmann, Rudiger
    • Bulletin of the Korean Chemical Society
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    • v.34 no.2
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    • pp.629-632
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    • 2013
  • Many properties of inorganic compounds are sensitive to changes in the point-defect concentrations. In minerals, such changes are influenced by temperature, pressure, and chemical impurities. Olivines form an important class of minerals and are magnesium-rich solid solutions consisting of the orthosilicates forsterite $Mg_2SiO_4$ and the fayalite $Fe_2SiO_4$. Orthosilicates have an orthorhombic crystal structure and exhibit anisotropic electronic and ionic transport properties. We examined the anisotropy of the electrical conductivity of $Fe_2SiO_4$ under the assumption that the electronic conduction in $Fe_2SiO_4$ occurs via a small polaron hopping mechanism. The anisotropic electrical conductivity is well explained by the electron transfer integrals obtained from the spin dimer analysis based on tight-binding calculations. The latter analysis is expected to provide insight into the anisotropic electrical conductivities of other magnetic insulators of transition metal oxides.

Structural and temperature coefficient of resistance characteristics of colossal magnetoresistance Mn oxides prepared by RF sputtering

  • Choi, Sun-Gyu;Ha, Tae-Jung;Reddy, A.Sivasankar;Yu, Byoung-Gon;Park, Hyung-Ho
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2007.11a
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    • pp.361-361
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    • 2007
  • A lot of efforts have been paid to develop infrared imaging systems in last decades. Bolometer has a wide range of applications from military to commercial, such as military night vision, medical imaging system and so on. Bolometer is a resistive sensor that detects temperature changes through resistance change. To improve detecting ability, bolometer should have a good resistive film which has high temperature coefficient of resistance (TCR) value. Colossal magnetoresistance (CMR) $L_{1-x}A_xMnO_3$ (where L and A are trivalent rare-earth ions and divalent alkaline earth ions, respectively.) are received attention to apply bolometer resistive film because it has a high TCR property which was discovered in the metal to semiconductor phase transition temperature region. In this work, CMR films were deposited on various substrates in relative low substrate temperature by RF magnetron sputtering. The influence of deposition parameters such as substrate temperature, gas partial pressure, and so on have been studied. The structural and TCR properties of the films were also investigated for applying to microbolometer.

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The Charge/Discharge for Metal Oxides Substitution and Doping of $Li_4Ti_5O_{12}$ ($Li_4Ti_5O_{12}$에서 금속 산화물 치환에 따른 충방전 효과)

  • Kang, Mi-Ra;Jee, Mi-Jung;Bae, Hyeon;Choi, Byung-Hyun;Kim, Sei-Ki;Lee, Mi-Jea
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2006.06a
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    • pp.44-45
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    • 2006
  • 초고용량 캐패시터(Supercapacitor)는 이차전지와 더불어 차세대 전지로 분류되는 신형에너지 장치로서 충 방전 속도가 다르고 순간 전력공급이 가능하며 충 방전 수명이 반영구적으로 길고 고출력을 내기 때문에 이차전지가 갖지 못하는 영역에서 동력에너지원으로 사용된다. 본 연구에서는 초고용랑 캐패시터의 전극소재인 탄소계 재료를 대신하여 비탄소계 전극소재인 $Li_4Ti_5O_{12}$의 고상법 제조를 위한 Li/Ti의 최적 조성과 혼합 방법으로 Li-Ti 계에 $Fe_2O_3$, NiO, $Nb_2O_5$, $Sb_2O_3$ 그리고 ZnO와 같은 금속산화물로 치환시켜 합성된 Li -Ti계 금속산화물의 특성 및 충 방전 효과에 미치는 영향을 관찰하고자 하였다.

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Linear and Nonlinear Optical Properties of Vanadium Pentoxide Films Prepared by Pulsed-Laser Deposition

  • Cui, Liqi;Wang, Ruiteng;Wang, Weitian
    • Korean Journal of Materials Research
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    • v.31 no.7
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    • pp.382-385
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    • 2021
  • Well-crystallized vanadium pentoxide V2O5 thin films are fabricated on MgO single crystal substrates by using pulsed-laser deposition technique. The linear optical transmission spectra are measured and found to be in a wavelength range from 300 to 800 nm; the data are used to determine the linear refractive index of the V2O5 films. The value of linear refractive index decreases with increasing wavelength, and the relationship can be well explained by Wemple's theory. The third-order nonlinear optical properties of the films are determined by a single beam z-scan method at a wavelength of 532 nm. The results show that the prepared V2O5 films exhibit a fast third-order nonlinear optical response with nonlinear absorption coefficient and nonlinear refractive index of 2.13 × 10-10 m/W and 2.07 × 10-15 cm2/kW, respectively. The real and imaginary parts of the nonlinear susceptibility are determined to be 3.03 × 10-11 esu and 1.12 × 10-11 esu, respectively. The enhancement of the nonlinear optical properties is discussed.

Triallyl Borate as an Effective Separator/Cathode Interphase Modifier for Lithium-ion Batteries

  • Ha Neul Kim;Hye Rim Lee;Taeeun Yim
    • Journal of Electrochemical Science and Technology
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    • v.14 no.3
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    • pp.272-282
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    • 2023
  • Ni-rich layered oxides cathode has recently gained attention as an advanced cathode material due to their applicable energy density. However, as the Ni component in the layered site is increased, the high reactivity of Ni4+ results in parasitic reaction associated with decomposing electrolyte, which leads to a rapid decreasing the lifespan of the cell. The electrolyte additive triallyl borate (TAB) improves interfacial stability, leading to a stable cathode-electrolyte interphase (CEI) layer on the LNCM83 cathode. A multi-functionalized TAB additive can produce a uniformly distributed CEI layer via electrochemical oxidation, which implies an increase in long-term cycling performance. After 100 cycles at elevated temperature, the cell tested by 0.75 TAB retained 88.3% of its retention ratio, whereas the cell performed by TAB-free electrolyte retained 64.1% of its retention. Once the TAB additive formed CEI layers on the LNCM83 cathode, it inhibited the decomposition of carbonate-based solvents species in addition to the dissolution of transition metal components from the cathode. The addition of TAB to LNCM83 cathode material is believed to be a promising way to increase the electrochemical performance.

Performance variation of Nickel-Cobalt-Manganese lithium-ion battery by cathode surface coating materials (NCM 리튬 이온 배터리의 양극 표면 코팅물질에 따른 성능변화 )

  • JinUk Yoo;Sung Gyu Pyo
    • Journal of the Korean institute of surface engineering
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    • v.57 no.2
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    • pp.57-70
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    • 2024
  • Nickel-cobalt-manganese (NCM) lithium-ion batteries(LIBs) are increasingly prominent in the energy storage system due to their high energy density and cost-effectiveness. However, they face significant challenges, such as rapid capacity fading and structural instability during high-voltage operation cycles. Addressing these issues, numerous researchers have studied the enhancement of electrochemical performance through the coating of NCM cathode materials with substances like metal oxides, lithium composites, and polymers. Coating these cathode materials serves several critical functions: it acts as a protection barrier against electrolyte decomposition, mitigates the dissolution of transition metals, enhances the structural integrity of the electrode, and can even improve the ionic conductivity of the cathode. Ultimately, these improvements lead to better cycle stability, increased efficiency, and enhanced overall battery life, which are crucial for the advancement of NCM-based lithium-ion batteries in high-demand applications. So, this paper will review various cathode coating materials and examine the roles each plays in improving battery performance.

Investigation on Ferroelectric and Magnetic Properties of Pb(Fe1/2Nb1/2)O3 Fe-Site Engineered with Antisymmetric Exchange Interaction (반대칭 교환 상호작용을 갖도록 Fe-Site가 제어된 PbFe1/2Nb1/2O3의 강유전/자기적 특성 연구)

  • Park, Ji-Hun;Lee, Ju-Hyeon;Cho, Jae-Hyeon;Jang, Jong Moon;Jo, Wook
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.35 no.3
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    • pp.297-302
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    • 2022
  • We investigated the origin of magnetic behaviors induced by an asymmetric spin exchange interaction in Fe-site engineered lead iron niobate [Pb(Fe1/2Nb1/2)O3, PFN], which exhibits a room-temperature multiferroicity. The magnitude of spin exchange interaction was regulated by the introduced transition metals with a distinct Bohr magneton, i.e., Cr, Co, and Ni. All compositions were found to have a single-phase perovskite structure keeping their ferroelectric order except for Cr introduction. We discovered that the incorporation of each transition metal imposes a distinct magnetic behavior on the lead iron niobate system; antiferro-, hard ferro-, and soft ferromagnetism for Cr, Co, and Ni, respectively. This indicates that orbital occupancy and interatomic distance play key roles in the determination of magnetic behavior rather than the magnitude of the individual Bohr magneton. Further investigations are planned, such as X-ray absorption spectroscopy, to clarify the origin of magnetic properties in this system.

Visible Light-based Photocatalytic Degradation by Transition Metal Oxide (전이 금속 산화물을 이용한 가시광선 기반 광촉매 분해)

  • Lee, Soomin;Park, Yeji;Lee, Jae Hun;Patel, Rajkumar
    • Membrane Journal
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    • v.29 no.6
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    • pp.299-307
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    • 2019
  • Photocatalysis is an environment friendly technique for degrading organic dyes in water. Tungsten oxide is becoming an active area of research in photocatalysis nanomaterials for having a smaller bandgap than the previously favored titanium dioxide. Synthesis of hierarchical structures, doping platinum (Pt), coupling with nanocomposites or other semiconductors are investigated as valid methods of improving the photocatalytic degradation efficiency. These impact the reaction by creating a redshift in the wavelength of light used, effecting charge transfer, and the formation/recombination of electron-hole pairs. Each of the methods mentioned above are investigated in terms of synthesis and photocatalytic efficiency, with the simplest being modification on the morphology of tungsten oxide, since it does not need synthesis of other materials, and the most efficient in photocatalytic degradation being complex coupling of metal oxides and carbon composites. The photocatalysis technology can be incorporated with water purification membrane by modularization process and applied to advanced water treatment system.

Tungsten oxide interlayer for hole injection in inverted organic light-emitting devices

  • Kim, Yun-Hak;Park, Sun-Mi;Gwon, Sun-Nam;Kim, Jeong-Won
    • Proceedings of the Korean Vacuum Society Conference
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    • 2010.02a
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    • pp.380-380
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    • 2010
  • Currently, organic light-emitting diodes (OLEDs) have been proven of their readiness for commercialization in terms of lifetime and efficiency. In accordance with emerging new technologies, enhancement of light efficiency and extension of application fields are required. Particularly inverted structures, in which electron injection occurs at bottom and hole injection on top, show crucial advantages due to their easy integration with Si-based driving circuits for active matrix OLED as well as large open area for brighter illumination. In order to get better performance and process reliability, usually a proper buffer layer for carrier injection is needed. In inverted top emission OLED, the buffer layer should protect underlying organic materials against destructive particles during the electrode deposition, in addition to increasing their efficiency by reducing carrier injection barrier. For hole injection layers, there are several requirements for the buffer layer, such as high transparency, high work function, and reasonable electrical conductivity. As a buffer material, a few kinds of transition metal oxides for inverted OLED applications have been successfully utilized aiming at efficient hole injection properties. Among them, we chose 2 nm of $WO_3$ between NPB [N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine] and Au (or Al) films. The interfacial energy-level alignment and chemical reaction as a function of film coverage have been measured by using in-situ ultraviolet and X-ray photoelectron spectroscopy. It turned out that the $WO_3$ interlayer substantially reduces the hole injection barrier irrespective of the kind of electrode metals. It also avoids direct chemical interaction between NPB and metal atoms. This observation clearly validates the use of $WO_3$ interlayer as hole injection for inverted OLED applications.

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Investigation of Electronic Structures of TCr2O4 (T = Fe, Co, Ni) Spinel Oxides by Employing Soft X ray Synchrotron Radiation Spectroscopy (연 X선 방사광 분광법을 이용한 TCr2O4(T = Fe, Co, Ni) 스피넬 산화물의 전자구조 연구)

  • Kim, Hyun Woo;Hwang, Jihoon;Kim, D.H.;Lee, Eunsook;Kang, J.S.
    • Journal of the Korean Magnetics Society
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    • v.23 no.5
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    • pp.149-153
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    • 2013
  • The electronic structures of $TCr_2O_4$ (T = Fe, Co, Ni) spinel oxides have been investigated by employing synchrotron radiation-based soft X ray absorption spectroscopy (XAS). The measured 2p XAS spectra of transition-metal ions reveal that Cr ions are trivalent ($Cr^{3+}$), and all the T (T = Fe, Co, Ni) ions are divalent ($Fe^{2+}$, $Co^{2+}$, $Ni^{2+}$). It is also found that most of T (T = Fe, Co, Ni) ions occupy the A sites under the tetrahedral symmetry, while Cr ions occupy mainly the B sites under the octahedral symmetry. These findings show that the structures of $TCr_2O_4$ (T = Fe, Co, Ni) are very close to the normal spinel structures. Based on these findings, it is expected that Jahn-Teller (JT) effects are important in $FeCr_2O_4$ and $NiCr_2O_4$. In contrast, $CoCr_2O_4$ maintains the cubic structure without having the JT distortion since both $Cr^{3+}$ and $Co^{2+}$ ions are non-JT ions. This work suggests that the antiferromagnetic interaction between $Cr^{3+}$ and $T^{2+}$ ions plays an important role in determining the magnetic properties of $TCr_2O_4$ (T = Fe, Co, Ni).