• Title/Summary/Keyword: Perovskite Phase

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Nanomaterials for Advanced Electrode of Low Temperature Solid Oxide Fuel Cells (SOFCs)

  • Ishihara, Tatsumi
    • Journal of the Korean Ceramic Society
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    • v.53 no.5
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    • pp.469-477
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    • 2016
  • The application of nanomaterials for electrodes of intermediate temperature solid oxide fuel cells (SOFC) is introduced. In conventional SOFCs, the operating temperature is higher than 1073 K, and so application of nanomaterials is not suitable because of the high degradation rate that results from sintering, aggregation, or reactions. However, by allowing a decrease of the operating temperature, nanomaterials are attracting much interest. In this review, nanocomposite films with columnar morphology, called double columnar or vertically aligned nanocomposites and prepared by pulsed laser ablation method, are introduced. For anodes, metal nano particles prepared by exsolution from perovskite lattice are also applied. By using dissolution and exsolution into and from the perovskite matrix, performed by changing $P_{O2}$ in the gas phase at each interval, recovery of the power density can be achieved by keeping the metal particle size small. Therefore, it is expected that the application of nanomaterials will become more popular in future SOFC development.

Synthesis and Conductivity Properties of LaNiO$_3$ Ceramic Conductors (LaNiO$_3$전도성 세라믹의 합성과 도전특성)

  • 조정호;조주현;김강언;정수태
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2001.11a
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    • pp.406-409
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    • 2001
  • The conductivity properties and synthesis of LaNiO$_3$ ceramics from La$\sub$1+$\delta$/NiO$_3$($\delta$=--0.06, 0, 0.06) were investigated. A single perovskite phase was realized at 800$^{\circ}C$. La$_2$NiO$_4$ and other unexpected oxide were observed at 1000$^{\circ}C$. The Microstructure was showed clearly that it is a low density porous material. LaNiO$_3$ ceramic showed a metallic conductivity. The conductivity of La rich samples had a higher value than the La poor samples.

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Electrical properties of PZT thin films deposited on corning glass substrates (Corning glass 기판위에 증착된 PZT 박막의 전기적 특성)

  • Ju, Pil-Yeon;Jeong, Kyu-Won;Park, Young;Kim, Hong-Joo;Park, Ki-Yup;Song, Joon-Tae
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2000.11a
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    • pp.263-266
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    • 2000
  • Effects of excess Pb(50 mole %) on the crystallization properties of amorphous PZT thin films on the glass substrates by post-annealing in oxygen ambient were investigated to lower the crystallization temperature of the PZT thin films with a single perovskite phase. The PZT thin films(350nm) were prepared on Pt/Ti/corning glass(1737) substrates. The PZT thin films and bottom electrode were deposited by RF magnetron sputtering. Crystallization properties of PZT thin films were strongly dependent on RTA(Rapid Thermal Annealing) temperature. We were able to obtain a perovskite structure of PZT at 600$^{\circ}C$ for 10min. After thermal treatments were done, electrical properties such as I-V, P-E, and fatigue were measured.

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Preparation of the Hollow Fiber Type Perovskite Catalyst for Methane Complete Oxidation (메탄의 완전산화 반응을 위한 중공사형 페롭스카이트 촉매 제조)

  • Lee, Seong Woon;Kim, Eun Ju;Lee, Hong Joo;Park, Jung Hoon
    • Korean Chemical Engineering Research
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    • v.56 no.3
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    • pp.297-302
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    • 2018
  • Bead type and hollow fiber type catalyst (HFC, Hollow Fiber type Catalyst) was prepared by $La_{0.1}Sr_{0.9}Co_{0.2}Fe_{0.8}O_{3-{\delta}}$ (LSCF1928) perovskite powder catalyst which showed excellent methane complete oxidation characteristics through previous studies. The HFC have a cylindrical shape with an empty interior, and pores can be formed through Phase inversion method so the specific surface area can be remarkably improved. In the case of the bead type catalyst prepared by adding Methyl Cellulose (MC), $SrCO_3$ was produced in addition to the original catalyst composition of LSCF1928 due to the reaction of $CO_2$ emitted from MC and Sr of the catalyst. In the case of the HFC, a single phase perovskite structure was obtained without impurities. The HFC calcined at $700{\sim}900^{\circ}C$ showed pore structure of finger-sponge-finger structure, and 99.9% oxygen conversion rate was achieved through complete oxidation of methane at $475^{\circ}C$. Air gap and spinning pressure condition were changed to control the HFC pore. 2 cm air gap and 7 bar spinning pressure showed the best catalytic performance and achieved oxygen conversion rates of more than 70.65%, 93.01%, and 99.99% at $425^{\circ}C$, $450^{\circ}C$ and $475^{\circ}C$, respectively.

A Study on the Catalytic Characteristics of Oxygen Reduction in an Alkaline Fuel Cell I. Synthesis of La0.6Sr0.4Co1-xFexO3 and Reduction Reaction of Oxygen (알칼리형 연료전지에서 산소환원에 미치는 촉매 특성 연구 I. La0.6Sr0.4Co1-xFexO3의 합성과 산소환원반응)

  • Moon, Hyeung-Dae;Lee, Ho-In
    • Applied Chemistry for Engineering
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    • v.7 no.3
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    • pp.543-553
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    • 1996
  • Oxygen reduction in an alkaline fuel cell was studied by using perovskite type oxides as an oxygen electrode catalyst. The high surface area catalysts were prepared by malic acid method and had a formula of $La_{0.6}Sr_{0.4}Co_{1-x}Fe_xO_3$(x=0.00, 0.01, 0.10, 0.20, 0.35 and 0.50). From the result of XRD pattern and specific surface area due to the amount of Fe substitution and the consumption of ammonia-water, the complex formation of Fe ion with $NH_3$ was the main factor for both the phase stability of perovskite and the increase of specific surface area. Multi-step calcination was necessary to give a single phase of perovskite in catalyst precursor. The crystal structure of the catalysts was simple cubic perovskite, which was verified from the XRD patterns of the catalysts. The activity of oxygen reduction was monitored by the techniques of cyclic voltammetry, static voltage-current method, and current interruption method. The activity(current density) of oxygen reduction showed its minimum at x=0.01 and its maximum between 0.20 and 0.35 of x-value in $La_{0.6}Sr_{0.4}Co_{1-x}Fe_xO_3$. This tendency was independent of the change of surface area.

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Oxygen Permeation Properties and Phase Stability of Co-Free $La_{0.6}Sr_{0.4}Ti_{0.2}Fe_{0.8}O_{3-{\delta}}$ Oxygen Membrane

  • Kim, Ki-Young;Park, Jung-Hoon;Kim, Jong-Pyo;Son, Sou-Hwan;Park, Sang-Do
    • Korean Membrane Journal
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    • v.9 no.1
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    • pp.34-42
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    • 2007
  • A perovskite-type ($La_{0.6}Sr_{0.4}Ti_{0.2}Fe_{0.8}O_{3-{\delta}}$) dense ceramic membrane was prepared by polymerized complex method, using citric acid as a chelating agent and ethylene glycol as an organic stabilizer. Effect of Ti addition on lanthanum-strontium ferrite mixed conductor was investigated by evaluating the thermal expansion coefficient, the oxygen flux, the electrical conductivity, and the phase stability. The thermal expansion coefficient in air was $21.19\;{\times}\;10^{-6}/K$ at 473 to 1,223 K. At the oxygen partial pressure of 0.21 atm ($20%\;O_2$), the electrical conductivity increased with temperature and then decreased after 973 K. The decrement in electrical conductivity at high temperatures was explained by a loss of the lattice oxygen. The oxygen flux increased with temperature and was $0.17\;mL/cm^2{\cdot}min$ at 1,223 K. From the temperature-dependent oxygen flux data, the activation energy of oxygen ion conduction was calculated and was 80.5 kJ/mol at 1,073 to 1,223 K. Also, the Ti-added lanthanum-strontium ferrite mixed conductor was structurally and chemically stable after 450 hours long-term test at 1,173 K.

Sintering Properties of the $Mg_5Ta_4O_{15}$ Ceramics with $Li_2CO_3$ Additions ($Li_2CO_3$ 첨가에 따른 $Mg_5Ta_4O_{15}$ 세라믹스의 소결 특성)

  • Kim, Jae-Sik;Choi, Eui-Sun;Ryu, Ki-Won;Lee, Young-Hie
    • Proceedings of the KIEE Conference
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    • 2008.05a
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    • pp.175-176
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    • 2008
  • In this study, the sintering properties and structural properties of the $Mg_5Ta_4O_{15}$cation-deficient perovskite ceramics with $Li_2CO_3$ additions are investigated. The cation-deficient perovskite ceramics are prepared through the solid-state route. According to the XRD pattern, $Mg_4Ta_2O_9$, $MgTa_2O_6$ and $Mg_5Ta_4O_{15}$ phase existed in sintered pure $Mg_5Ta_4O_{15}$ ceramics. With $Li_2CO_3$, additions, the peak intensities of $Mg_4Ta_2O_9$ and $MgTa_2O_6$ phase were reduced. Also, diffraction intensity of the $Mg_5Ta_4O_{15}$ phase was increased with increments of $Li_2CO_3$ additions. The bulk densities were increased with increasing of $Li_2CO_3$ amount and approach the theoretical density of the $Mg_5Ta_4O_{15}$ ceramics, more and more. Microstructure of the $Mg_5Ta_4O_{15}$ ceramics were densified more and more by additions of $Li_2CO_3$. The bulk density of $Mg_5Ta_4O_{15}$+5wt% $Li_2CO_3$ ceramics sintered at $1500^{\circ}C$ for 10 hours was $5.88g/cm^3$.

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Structure and Electrical Properties of 0.85NaNbO3-0.15LiNbO3 Ceramics (0.85NaNbO3-0.15LiNbO3 세라믹스의 구조 및 전기적 특성)

  • Jeon, Chang Jun;Jeong, Young Hun;Yun, Ji Sun;Nam, Joong Hee;Paik, Jong Hoo;Cho, Jeong Ho
    • Journal of Sensor Science and Technology
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    • v.23 no.2
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    • pp.105-109
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    • 2014
  • Structure and electrical properties of $0.85NaNbO_3-0.15LiNbO_3$ ($(Li_{0.15}Na_{0.85})NbO_3$) ceramics were investigated as a function of sintering temperature. $(Li_{0.15}Na_{0.85})NbO_3$ ceramics were prepared by conventional solid state processing. A main phase of the orthorhombic perovskite structure and secondary phase of $LiNbO_3$ were confirmed for all sintered specimens. Dense $(Li_{0.15}Na_{0.85})NbO_3$ ceramics were obtained at sintering temperature above $1050^{\circ}C$. With increasing sintering temperature, the electromechanical coupling factor ($k_p$), piezoelectric constant ($d_{33}$) and relative dielectric constant (${\varepsilon}_r$) of the sintered specimens increased, while the mechanical quality factor ($Q_m$) decreased. These results are due to the increase of grain size and crystallite size of orthorhombic perovskite structure. Based on the temperature dependence of ${\varepsilon}_r$, stable piezoelectric properties were expected because no phase transition found up to $300^{\circ}C$. Typically, kp of 18%, $d_{33}$ of 34.7 pC/N, ${\varepsilon}_r$ of 135, and $Q_m$ of 62.8 were obtained for the specimens sintered at $1200^{\circ}C$ for 5 h.

Secondary Phase Control of Lithium Ion-Substituted Potassium Niobate Ceramics via Stoichiometry Modification (화학양론 변화를 통한 리튬 이온 치환 니오브산 칼륨 세라믹의 이차상 제어 연구)

  • Tae Soo Yeo;Ju Hyeon Lee;Wook Jo
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.37 no.5
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    • pp.533-540
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    • 2024
  • In line with the development of electronic devices and technologies, the demand for improving ferroelectric materials' performance is increasing. Since K0.5Na0.5NbO3 (KNN), an eco-friendly ferroelectric material that does not use lead and has a high Curie temperature, it is attracting attention to its usability as a high-temperature dielectric, and various studies are being conducted to increase performance. In a KNN having a perovskite structure, there was a simulation result that the KNN has higher spontaneous polarization when the A-site in which sodium ions exist is replaced with lithium ions. If the simulation results can be proven experimentally, the application range of KNN-based ferroelectric materials will increase. To this end, we tried to manufacture a K1-xLixNbO3 (KLN) with high electrical characteristics by fabricating niobium-deficient and potassium-excessive compositions, which attempt was made to solve the stoichiometry problem by volatilization and suppress secondary phases. If KLN's secondary phase suppression and relative permittivity improvement are successful, it will contribute to meeting the demand for developing electronic devices.

Antiferroelectric and antiferrodistortive phase transitions in Ruddlesden-Popper Pb2TiO4 from first-principles

  • Xu, Tao;Shimada, Takahiro;Wang, Jie;Kitamura, Takayuki
    • Coupled systems mechanics
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    • v.6 no.1
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    • pp.29-40
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    • 2017
  • This work employed density functional theory to investigate the structural and ferroelectric properties of the Ruddlesden-Popper (RP) phase of lead titanate, $Pb_2TiO_4$, as well as its phase transitions with epitaxial strain. A wealth of novel structural instabilities, which are absent in the host $PbTiO_3$ material, were identified in the RP phase through phonon soft-mode analysis. Our calculations showed that the ground state of $Pb_2TiO_4$ is antiferroelectric, distinct from the dominant ferroelectric phase in the corresponding host material. In addition, applied epitaxial strain was found to play a key role in the interactions among the instabilities. The induction of a sequence of antiferroelectric and antiferrodistortive (AFD) phase transitions by epitaxial strain was demonstrated, in which the ferroic instability and AFD distortion were cooperative rather than competitive, as is the case in the host $PbTiO_3$. The RP phase in conjunction with strain engineering thus represents a new approach to creating ferroic orders and modifying the interplay among structural instabilities in the same constituent materials, enabling us to tailor the functionality of perovskite oxides for novel device applications.