• Journal of the Korean Ceramic Society
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• v.52 no.4
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• pp.237-242
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• 2015

$Bi_{0.5}(Na_{0.78}K_{0.22})_{0.5}TiO_3$ (BNKT) lead-free piezoelectric ceramics modified by $LaMnO_3$ (LM) were fabricated by conventional solid-state method. The crystal structure and the morphology of the lead free ceramics were analyzed by XRD (X-ray diffraction) and FE-SEM (Field Emission Scanning Electron Microscopy). The LM modified BNKT ceramics have a phase transition from ferroelectric tetragonal to non-polar pseudo-cubic. Despite decreases in the remnant polarization ($P_r$) and coercive field ($E_c$) in the P-E hysteresis loops, the electric-field induced strain properties were significantly enhanced by the LM modification. The highest value of $S_{max}/E_{max}=412pm/V$ at an applied electric field of 5 kV/mm was found in BNKT-0.01LM ceramic.

• Bulletin of the Korean Chemical Society
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• v.19 no.6
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• pp.661-666
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• 1998

Active reaction sites and electrochemical O2 reduction kinetics on La_{1-x}Sr_xMnO_{3+{\delta}} (x=0.1-0.4)/YSZ (yttria-stabilized zirconia) electrodes are investigated in the temperature range of 700-900 ℃ at $Po_2=10^{-3}$-0.21 atm. Results of the steady-state polarization measurements, which are formulated into the Butler-Volmer formalism to extract transfer coefficient values, lead us to conclude that the two-electron charge transfer step to atomically adsorbed oxygen is rate-limiting. The same conclusion is drawn from the $Po_2$-dependent ac impedance measurements, where the exponent m in the relationship of $I_o$ (exchange current density) ∝ $P_{o_{2}}^m$ is analyzed. Chemical analysis is performed on the quenched Mn perovskites to estimate their oxygen stoichiometry factors (δ) at the operating temperature (700-900 ℃). Here, the observed δ turns out to become smaller as both the Sr-doping contents (x) and the measured temperature increase. A comparison between the 8 values and cathodic activity of Mn perovskites reveals that the cathodic transfer coefficients $({\alpha}_c)$ for oxygen reduction reaction are inversely proportional to δ whereas the anodic ones $({\alpha}_a)$ show the opposite trend, reflecting that the surface oxygen vacancies on Mn perovskites actively participate in the $O_2$ reduction reaction. Among the samples of x= 0.1-0.4, the manganite with x=0.4 exhibits the smallest 8 value (even negative), and consistently this electrode shows the highest ${\alpha}_c$ and the best cathodic activity for the oxygen reduction reaction.

• Journal of Energy Engineering
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• v.19 no.2
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• pp.73-80
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• 2010

A solid oxide fuel cells(SOFC) is a clean energy technology which directly converts chemical energy to electric energy. When the SOFC is used in cogeneration then the efficiency can reach higher than 80%. Also, it has flexibility in using various fuels like natural gases and bio gases, so it has an advantage over polymer electrolyte membrane fuel cells in terms of fuel selection. A typical cathode material of the SOFC in conjunction with yttria stabilized zirconia(YSZ) electrolyte is still Sr-doped $LaMnO_3$(LSM). Recently, application of mixed electronic and ionic conducting perovskites such as Sr-doped $LaCoO_3$(LSCo), $LaFeO_3$(LSF), and $LaFe_{0.8}Co_{0.2}O_3$(LSCF) has drawn much attention because these materials exhibit lower electrode impedance than LSM. However, chemical reaction occurs at the manufacturing temperature of the cathode when these materials directly contact with YSZ. In addition, thermal expansion coefficient(TEC) mismatch with YSZ is also a significant issue. It is important, therefore, to develop cathode materials with good chemical stability and matched TEC with the SOFC electrolyte, as well as with high electrochemical activity.

• Korean Chemical Engineering Research
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• v.49 no.2
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• pp.168-174
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• 2011

Various La-based perovskite catalysts were prepared by a Pechini method, and they were applied to the low-temperature oxidation of odor compounds exhausted from waste food treatment process for effective deodorization. Quantitative and qualitative analyses of exhausted gas were conducted to measure the amount of major odor compounds with respect to operation time. A standard odor sample composed of major odor compounds was then prepared for use as a feed for oxidation reaction system. Various transition metal(M)-substituted La-based perovskite catalysts ($LaMO_{3}$: M=Cr, Mn, Fe, Co, and Ni) were prepared and applied to the oxidation of odor compounds in order to investigate the $LaNiO_3$ catalyst showed the best catalytic performance. Pt-substituted perovskite catalysts ($LaNi_{1-x}Pt_{x}O_{3}$: x=0, 0.03, 0.1, and 0.3) were then prepared for enhancing the catalytic performance. It was found that $LaNi_{0.9}Pt_{0.1}O_{3}$ catalyst served as the most efficient catalyst. Supported perovskite catalysts ($XLaNi_{0.9}Pt_{0.1}O_{3}/Al_{2}O_{3}$: X=perovskite content(wt%), 0, 10, 20, 30, 40, 50, and 100) were finally applied for the purpose of maximizing the catalytic performance of perovskite catalyst in the low-temperature oxidation reaction. Catalytic performance of $XLaNi_{0.9}Pt_{0.1}O_{3}/Al_{2}O_{3}$ catalysts showed a volcano-shaped curve with respect to perovskite content. Among the catalysts tested, $20LaNi_{0.9}Pt_{0.1}O_{3}$/$Al_{2}O_{3}$ catalyst exhibited the highest conversion of odor compounds of 88.7% at $180^{\circ}C$.

• Journal of Sensor Science and Technology
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• v.6 no.1
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• pp.63-71
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• 1997

The thin-film eletroluminescent (TFEL) device having the stacked structure of ZnS:Mn/$ZnS:TbF_{3}$ has been fabricated. Insulate layers used (Pb,La)$TiO_{3}$ and $SiO_{2}$ thin films. The emission color was white. The TFEL device employing ZnS:Mn/$ZnS:TbF_{3}(8000{\AA})$ stacked phosphor layers showed the threshold voltage of $78V_{rms}$. And the brightness of the TFEL device was $400{\mu}W/cm^{2}$ at the applied voltage of $100V_{rms}$. The emission spectrum of TFEL device had a wavelength from 450nm to 620nm. The manufactured devices can be a practical use as a TFEL devices of red, green and blue by using the color filters.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.12
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• pp.2255-2261
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• 2000

To eliminate $NO_x$ in diesel emission. selective catalyst reduction (SCR) was used in real diesel engine. Among the SCR methods, metal oxide and perovskite catalysts were introduced in this paper. The removal efficiencies with various major, promoter catalysts on ${\gamma}-Al_2O_3$ at different reaction temperature were investigated, and $LaCuMnO_x$ catalyst which has high removal efficiency at the temperature of real diesel exhaust gas was selected. $NO_x$ reduction was carried out over these catalysts in the flow-through type reactor using by-pass ($SV=3,300h^{-1}$). Under the given condition to this study, perovskite catalysts showed considerably high removal efficiency and $LaCuMnO_x$ was the best one among these catalysts in the temperature range of $150{\sim}450^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.36 no.2
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• pp.145-150
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• 1999

Gd1-xSrxMnO3(0$\leq$X$\leq$0.6) as the cathode for solid oxide fuel cell was synthesized by citrate process and studied for its crystal structure, electrical conductivity, thermal expansion coefficient (TEC), and investigated reactivity with 8 mol% yttria stabilized zirconia(8YSZ) or Ce0.8Gd0.2O1.9 (CGO). The crystal structure of Gd1-xSrxMnO3 changed from orthorhombic (0$\leq$X$\leq$0.3) through cubic (0.4$\leq$X$\leq$0.5) to tetragonal structure (X=0.6). When Sr contents was increased, the electrical conductivity of Gd1-xSrxMnO3 was inthose of La1-xSrxMnO3, 8YSZ and CGO if Sr content was above 30mol%. TEC of Gd1-xSrxMnO3 was increased with Sr content. After heat treatment at 1300$^{\circ}C$ for 48 hours, reaction product of Gd1-xSrxMnO3 and 8YSZ was SrZrO3. However CGO had no reaction product with Gd1-xSrxMnO3.

• Proceedings of the Korean Vacuum Society Conference
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• 2004.08a
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• pp.200-200
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• 2004

• Journal of Magnetics
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• v.6 no.1
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• pp.1-4
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• 2001

We have used acetic acids ethanol and distilled water as a solvent to synthesize $La_{2/3}Sr_{1/3}Mn_{0.99}{^{57}}Fe_{0.01}O_3$(LSMFO) precursor. Crack-free LSMFO granular polycrystalline thin films have been deposited on thermally oxidized silicon substrates by spin coaling. The dependence of crystallization, surface morphology, magnetic and transport properties on annealing temperature was investigated. With increasing annealing temperature, the metal-semiconductor (insulator) transition temperature and the magnetic moment decrease while the resistivity increases. The lattice constants remain almost unchanged. For LSMFO thin films, spin-dependent interfacial tunneling and/or scattering magnetoresistance were observed. Our results indicate that the annealing temperature is very important in determining the intrinsic and extrinsic magnetotransport properties.

• Proceedings of the Korean Magnestics Society Conference
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• 2005.06a
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• pp.199-199
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• 2005