• 한국세라믹학회지
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• 제44권3호
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• pp.137-141
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• 2007

$La_{2}O_{3}-TiO_{2}-SiO_{2}$ glass, a type that could not obtained so far by the conventional melting method, was prepared successfully using a sol gel process. Glass derived with the sol-gel process has compositions of $5La_{2}O_{3}-5TiO_{2}-90SiO_{2},\;5La_{2}O_{3}-10TiO_{2}-85SiO_{2}$, and $5La_{2}O_{3}-20TiO_{2}75SiO_{2}$. The UV-visible absorption edge of all glass compositions was below 400 nm. The measured density is in the range of 2.55-2.89, and was nearly identical to the calculated density and the refractive index of the glasses derived from the sol-gel ranges from 1.545 to 1.645. The molar additive coefficient of $TiO_{2}$ measured in this ternary system is lower than the calculated value, while the value of $La_{2}O_{3}$ is higher.

• 한국재료학회지
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• 제25권8호
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• pp.423-428
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• 2015

Impedancemetric $NO_x$ (NO and $NO_2$) gas sensors were designed with a stacked-layer structure and fabricated using $LaCr_xCo_{1-x}O_3$ (x = 0, 0.2, 0.5, 0.8 and 1) as the receptor material and $Li_{1.3}Al_{0.3}Ti_{1.7}(PO_4)_3$ plates as the solid-electrolyte transducer material. The $LaCr_xCo_{1-x}O_3$ layers were prepared with a polymeric precursor method that used ethylene glycol as the solvent, acetyl acetone as the chelating agent, and polyvinylpyrrolidone as the polymer additive. The effects of the Co concentration on the structural, morphological, and $NO_x$ sensing properties of the $LaCr_xCo_{1-x}O_3$ powders were investigated with powder X-ray diffraction, field emission scanning electron microscopy, and its response to 20~250 ppm of $NO_x$ at $400^{\circ}C$ (for 1 kHz and 0.5 V), respectively. When the as-prepared precursors were calcined at $700^{\circ}C$, only a single phase was detected, which corresponded to a perovskite-type structure. The XRD results showed that as the Co concentration of the $LaCr_xCo_{1-x}O_3$powders increased, the crystal structure was transformed from an orthorhombic phase to a rhombohedral phase. Moreover, the $LaCr_xCo_{1-x}O_3$ powders with $0{\leq}x<0.8$ had a rhombohedral symmetry. The size of the particles in the $LaCr_xCo_{1-x}O_3$powders increased from 0.1 to $0.5{\mu}m$ as the Co concentration increased. The sensing performance of the stack-structured $LaCr_xCo_{1-x}O_3/Li_{1.3}Al_{0.3}Ti_{1.7}(PO_4)_3$ sensors was found to divide the impedance component between the resistance and capacitance. The response of these sensors to NO gas was more sensitive than that to $NO_2$ gas. Compared to other impedancemetric sensors, the $LaCr_{0.8}Co_{0.2}O_3/Li_{1.3}Al_{0.3}Ti_{1.7}(PO_4)_3$ sensor exhibited good reversibility and reliable sensingresponse properties for $NO_x$ gases.

• Journal of Magnetics
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• 제16권2호
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• pp.101-103
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• 2011

Solid solutions between $BaTiO_3$ and $LaFeO_3$ have been prepared through a solid state reaction method. The X-ray diffraction results reveal that $Ba_{1-x}La_xTi_{1-x}Fe_xO_3$ ($0.1\;{\leq}\;x\;{\leq}\;0.7$) compounds have a cubic structure, whereas the parent material $BaTiO_3$ has a tetragonal structure. The magnetization measurements indicate that the materials have a magnetic ordering at room temperature and the magnetic properties of the solid solutions depending on the doping amount of $LaFeO_3$. The origin of magnetic behaviors is believed to be from $Fe^{3+}$ ions.

• 한국결정성장학회지
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• 제7권3호
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• pp.418-427
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• 1997

$La_2O_3$가 각각 0, 0.1, 0.3, 0.5, 0.7, 1, 3, 5 mole% 첨가된 $0.05pb(Sn_{0.5}Sb_{0.5})O_3＋0.11PbTiO_30.84PbZroO_3＋0.4Wt%MnO_2$ (이하 0.05PSS -0.11PT-0.84PZ+0.4wt%$MnO_2$)계를, $1250^{\circ}C$에서 $PbZrO_3$를 분위기 분말로 사용하여 성형체 무게의 1/2을 함께 넣고 소결체를 제조하여 그 특성을 분석하였다. 소결체의 밀도는 7.683 g/$\textrm {cm}^3$에서 7.515 g/$\textrm {cm}^3$ 범위였으며, 3 mole% $La_2O_3$를 첨가한 경우 가장 높은 값을 나타내었다. 0에서 5 mole% 범위에서 $La_2O_3$ 첨가량을 증가시킬 때 평균 입경이 9.0 $\mu \textrm{m}$에서 1.3 $\mu\textrm{m}$까지 감소되었다. 결정구조의 경우 $La_2O_3$첨가량을 0에서 1 mole%로 할 때 0.05PSS-0.11 PT-0,84PZ계에서 고용된 상을 형성하였으나 3, 5 mole%로 첨가량을 증가시킴에 따라 제2차 산이 형성되었고, 소결체를 $120^{\circ}C$ 또는 $140^{\circ}C$에서 $5 KV_{DC}$ /mm로 20분간 poling 전후에 $La_2O_3$ 첨가량이 0 에서 3 mlole%까지 증가될수록 1KHz에서의 유전 상수는 증가되었으며, 유전손실은 모든 경우에서 1 % 미만의 값을 나타내었다. $La_2$O$_3$첨가량이 0, 0.5, 1, 3 mole%로 증가됨에 따라 큐리온도가 208$^{\circ}C$, 183$^{\circ}C$, $152^{\circ}C$ 그리고 $127^{\circ}C$로 감소되었다. $La_2O_3$가 증가됨에 따라 대체로 $K_{p}$ 증가되었으며 0.7 mlole%의 $La_2O_3$를 첨가한 소결체를 $140^{\circ}C$에서 poling한 경우 가장 높은 $K_p$값으로 14.5 %를 나타내었다.

• 한국재료학회지
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• 제9권1호
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• pp.25-29
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• 1999

We have developed a laser molecular beam epitaxy system for the layer-by-layer growth of oxide thin films. Using this system, we could grow and control oxide thin films of LaAlO$_3$in a molecular layer epitaxy mode on the atomically flat SrTiO$_3$ substrate with a LaAlO$_3$single crystal target. Very clear RHEED oscillations were observed during to growth of a LaAlO$_3$ film for a long period under the optimized conditions of substrate temperature at $650^{\circ}C$, oxygen pressure at 1$\times$10\ulcorner torr, and an incident laser fluence of 4.6J/$\textrm{cm}^2$. The height of mono-layer-LaAlO$_3$ film grown during one period of RHEED intensity oscillation was 3.8$\AA$.

• 한국재료학회지
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• 제21권8호
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• pp.468-475
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• 2011

[ $LaMeO_3$ ](Me = Cr, Co) powders were prepared using the polymeric precursor method. The effects of the chelating agent and the polymeric additive on the synthesis of the $LaMeO_3$ perovskite were studied. The samples were synthesized using ethylene glycol (EG) as the solvent, acetyl acetone (AcAc) as the chelating agent, and polyvinylpyrrolidone (PVP) as the polymer additive. The thermal decomposition behavior of the precursor powder was characterized using a thermal analysis (TG-DTA). The crystallization and particle sizes of the $LaMeO_3$ powders were investigated via powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and particle size analyzer, respectively. The as-prepared precursor primarily has $LaMeO_3$ at the optimum condition, i.e. for a molar ratio of both metal-source (a : a) : EG (80a : 80a) : AcAc (8a) inclusive of 1 wt% PVP. When the as-prepared precursor was calcined at $700^{\circ}C$, only a single phase was observed to correspond with the orthorhombic structure of $LaCrO_3$ and the rhombohedral structure of $LaCoO_3$. A solid-electrolyte impedance-metric sensor device composed of $Li_{1.5}Al_{0.5}Ti_{1.5}(PO_4)_3$ as a transducer and $LaMeO_3$ as a receptor has been systematically investigated for the detection of NOx in the range of 20 to 250 ppm at $400^{\circ}C$. The sensor responses were able to divide the component between resistance and capacitance. The impedance-metric sensor for the NO showed higher sensitivity compared with $NO_2$. The responses of the impedance-metric sensor device showed dependence on each value of the NOx concentration.

• 대한전기학회논문지
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• 제44권5호
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• pp.644-648
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• 1995

Transparent xBa(La$_{1}$2/Nb$_{1}$2/)O$_{3}$-(1-x)Pb(Zr, Ti)O$_{3}$ (x=8.5, 9.0[mol.%], Zr/Ti=70/30~40/60) ceramics were fabricated by the two-stage sintering method, the electrooptic properties were investigated with Ba(La$_{1}$2/Nb$_{1}$2/)O$_{3}$ content and Zr/Ti composition ratio. Decreasing the Zr/Ti ratio, the electrooptic property was changed from a quadratic electrooptic effect to a linear electrooptic effcet. In the BLN-PZT 9.0/50/50 specimen having the tetragonal structure, the linear electrooptic coefficient had the highest value of 6.01*10$^{-10}$ [m/V] and in the BLN-PZT 9.0/55/45 specimen which located near the MPB region, the quadratic electrooptic coefficient had the highest value of 10.53*10$^{-16}$ [m$^{2}$/V$^{2}$].

• 한국세라믹학회지
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• 제29권11호
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• pp.900-904
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• 1992

High temperature electrical conductivity was measured for perovskite La0.98Sr0.02MnO3 at 200~130$0^{\circ}C$ as a function of Po2 and 1/T. Perovskite La1-xSrxMnO3 system is the typical oxygen electrode in solid oxide fuel cell (SOFC). Acetate precursors were used for the preparation of mixed water solution and the calcined powders were reacted with Na2CO3 flux in order to obtain highly reactive powders of perovskite La0.98Sr0.02MnO3. The relative density was greatly increased above 90% because of the homogeneous sintering. From the conductivity ($\sigma$)-temperature and conductivity-Po2 at constant temperature, the defect structure of La0.98Sr0.02MnO3 was discussed. From the slope of 1n($\sigma$) vs 1/T, the activation energy of 0.069 and 0.108eV were evaluated for above 40$0^{\circ}C$, respectively. From the relationship between $\sigma$ and Po2, it was found that the decomposition of La0.98Sr0.02MnO3 was occurred at 10-15.5 atm(97$0^{\circ}C$) and 10-11 atm(125$0^{\circ}C$). It is supposed that the improvement of p-type conductivity may be leaded by the increase of Mn4+ concentration through the substitution of divalent/monovalent cations for La site in LaMnO3.

• 한국수소및신에너지학회논문집
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• 제32권1호
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• pp.41-52
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• 2021

NiO and Co3O4-doped porous La(CoNi)O3 perovskite oxides were prepared from excess Ni addition by a hydrothermal method using porous silica template, and characterized as bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) for Zn-air rechargeable batteries in alkaline solution. Excess Ni induced to form NiO and Co3O4 in La(CoNi)O3 particles. The NiO and Co3O4-doped porous La(CoNi)O3 showed high specific surface area, up to nine times of conventionally synthesized perovskite oxide, and abundant pore volume with similar structure. Extra added Ni was partially substituted for Co as B site of ABO3 perovskite structure and formed to NiO and Co3O4 which was highly dispersed in particles. Excess Ni in La(CoNi)O3 catalysts increased OER performance (259 mA/㎠ at 2.4 V) in alkaline solution, although the activities (211 mA/㎠ at 0.5 V) for ORR were not changed with the content of excess Ni. La(CoNi)O3 with excess Ni showed very stable cyclability and low capacity fading rate (0.38 & 0.07 ㎶/hour for ORR & OER) until 300 hours (~70 cycles) but more excess content of Ni in La(CoNi)O3 gave negative effect to cyclability.

• 한국세라믹학회지
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• 제35권9호
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• pp.981-987
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• 1998

$La_{0.5}Sr_{0.5}MnO_{3-\delta}$ as air electrode for soild oxide fuel cell was synthesized by a citrate process and its cathodic polarization was determinated by the current interruption method on the Gd-doped ceria as electrolyte. The addition of citric acid increased the exothermic heat for the formation of $La_{0.5}Sr_{0.5}MnO_{3-\delta}$ perovskite oxide. The degree of the initial particle agglomeration was affected by the exothermic heat. Also the increase of cal-cination temperature enlarged the particle size and the higher sintering temperature accelerated the den-sification of $La_{0.5}Sr_{0.5}MnO_{3-\delta}$ layer after its being painted on $Ce_{0.8}Gd_{0.2}O_{1.9}$ electrolyte. In this study $La_{0.5}Sr_{0.5}MnO_{3-\delta}$ synthesized by citrate process of which the molar ratio of citric acid to metal nitrate was 2 calcined at $650^{\circ}C$ for 2hr and sintered at 1100 at $1200^{\circ}C$ for 4 hrs after slurry coating on Ce0.8Gd0.2O1.9 electrlyte showed the lowest cathodic polarization.