• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 추계학술대회 초록집
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• pp.80.1-80.1
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• 2010

A strontium titanate ($SrTiO_3$)-based material with a perovskite structure is considered to be one of the promising alternatives to $LaCrO_3$-based materials since $SrTiO_3$ perovskite shows a high chemical stability under both oxidizing and reducing atmospheres at high temperatures. $SrTiO_3$ materials exhibit an n-type semiconducting behavior when it is donor-doped and/or exposed to a reducing atmosphere. In this work, $Sr_{1-x}La_xTi_{1-y}M_yO_3$ materials doped with $La^{3+}$ in A-sites and aliovalent transition metal ions ($M^{n+}$) in B-sites were synthesized by the modified Pechini method. The X-ray diffraction analysis indicated that the materials synthesized by the Pechini process exhibited a single curbic perovskite-type structure without any impurity phases, and are tolerant, to some extent, to cation doping. The sintering behaviors of $Sr_{1-x}La_xTi_{1-y}M_yO_3$ in $H_2/N_2$ and air were characterized by dilatometry and microstructural observations. The electrical conduction mechanism and the dopant effect are discussed based on the defect structures and the electrical conductivities measured at various oxygen partial pressures and temperatures.

• The Korean Journal of Ceramics
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• 제3권2호
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• pp.116-123
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• 1997

A chemically stabilized $\beta$-cristobalite, which is stabilized by stuffing cations of $Ca^{2+}$ and $Al^{3+}$, was prepared by a solution-polymerization route employing Pechini resin or PVA solution as a polymeric carrier. The polymeric carrier affected the crystallization temperature, morphology of calicined powder, and particle size distribution. In case of the polyvinyl alcohol (PVA) solution process, a fine $\beta$-cristobalite powder with a narrow particle size distribution (average particle size : 0.3$\mu\textrm{m}$) and a BET specific surface area of 72 $\m^2$/g was prepared by an attrition-milling for 1 h after calcination at 110$0^{\circ}C$ for 1h. Wider particle size distribution and higher specific surface area were observed for the $\beta$-cristobalite powder derived from Pechini resin. The cubie(P1-to-tetraganalb) phase transformation in polynystalline $\beta$-cristobalite was induced at approximately 18$0^{\circ}C$. Like other materials showing transformation toughening, a critical size effect controlled the $\beta$-to-$\alpha$ transformation. Densifed cristobalite sample had some cracks in its internal texture after annealing. The cracks, occurred spontaneoulsy on cooling, were observed in the sample with an average grain sizes of 4.0 $\mu\textrm{m}$ or above. In case of the sintered cristobalite having a composition of CaO.$2Al_2O_3$.40SiO$_2$, small amount of amorphous phase and slow grain growth during annealing were observed. Shear stress-induced transformation was also observed in ground specimen. Cristobalite having a composition of CaO.2Al2O3.80SiO2 showed a more sensitive response to shear stress than the CaO.$2Al_2O_3$.40SiO$_2$ type cristobalite. Shear-induced transformation resulted in an increase of volume about 13% in $\alpha$-cristobalite phase on annealing for above 10 h in the case of the former composition.

• 한국세라믹학회지
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• 제39권6호
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• pp.604-609
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• 2002

분자 단위의 균일한 조성을 가지는 $BaCeO_3$ 나노 분말을 Pechini법에 기초한 citrate 공정을 통하여 합성하였다. 금속 이온의 chelating제로서 citric acid를, 반응 촉매로서는 ethylen glycol을 각각 사용하여 고분자 전구체를 형성시켰고, 이를 기반으로 $900^{\circ}C$의 온도에서 4시간동안 열처리하여 약 100nm의 균일한 크기와 형상을 가진, 사방정 구조의 단일상 $BaCeO_3$ 분말을 합성하는데 성공하였다. 잔존하는 미량의 $CO_3^{2-}$는 $1100^{\circ}C$ 이상의 온도에서 완전히 분해되었고, 이 때 평균 입도 는 약 2배 증가하였으나 매우 균일한 분포를 나타내었다.

• 한국세라믹학회지
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• 제34권6호
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• pp.652-658
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• 1997

The phase stability in the interface of Sr-doped LaMnO3(LSM)/Gd-doped CeO2(CGO) was examined in this study in order to check the feasibility of using LSM as the cathode material in a low-temperature SOFC(solid oxide fuel cell) using CGO as the electrolyte. For the purpose, CGO powders of Ce0.82Gd0.18O0.91 and two LSM powders having different compositions, La0.9Sr0.1MnO3(LSM10) and La0.5Sr0.5MnO3(LSM50), were synthesized using Pechini method. Then, specimens having the LSM/CGO interface were prepared, heat-treated at 130$0^{\circ}C$ for up to 3 days, and analyzed by XRD and STEM/EDX. Face-centered cubic CGO powders of less than 10 nm size were obtained by calcination of polymeric precursor formed in the process at 45$0^{\circ}C$. Higher calcination temperature of $700^{\circ}C$ was necessary for monoclinic LSM10 and cubic LSM50 powders. LSM powders were coarser than CGO and observed to be in the range of 50~100 nm. No trace of LSM-CGO interaction product was found in the XRD pattern. Also it was known from the concentration profile in the vicinity of the interface that interdiffusion was occurred over only a small penetration depth of ~100 nm order.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1998년도 PROCEEDINGS OF THE 14TH KACG TECHNICAL MEETING AND THE 5TH KOREA-JAPAN EMGS (ELECTRONIC MATERIALS GROWTH SYMPOSIUM)
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• pp.105-109
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• 1998

Langasite({{{{ { La}_{ 3} {Ga }_{5 } {SiO }_{14 } , LGS}}}}) powder was prepared by a polymerized complex method based on the Pechini-type reaction. A mixed solution of ethylene glycol(EG), cotric acid(CA), lanthanum, gallium and silicon ions, with a molar ratio of EG:CA:La:Ga:Si=100:25:3:5:1, was polymerzed to from a transparent resin, which was used as a precursor for the synthesis of LGS. X-ray diffraction(XRD) patterns indicated that the LGS phase could be formed by the heat-treatment in air at 1000$^{\circ}C$ for 3hrs

• 한국세라믹학회지
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• 제36권9호
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• pp.930-936
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• 1999

For LiMn2O4 based spinel structures the stoichiometric reaction conditions need be considered carefully because the electrical properties depend on the structural stability. In order to obtain the homogeneous compound the Pechini process was chosen which could obtain a stoichiometry phase even low temperature and dependency of the synthetic condition on structural stability and electrochemical performance was investigated. X-ray diffraction studies showed that the compounds doped with transition metal have smaller lattice constants than those un doped. The dc conductivity was evaluated by a four probe method in the low and high temperature region respectively. The variations of basal spacings for the cathode were detected to be dependent on the extent of current flows (under dc)

• 한국세라믹학회지
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• 제34권11호
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• pp.1182-1186
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• 1997

La0.8Ca0.2Cr0.98O3 powder was prepared using the modified Pechini process. Various crystalline phases formed during thermal decomposition were investigated. (La,Ca)CrO4 phase, first formed from the precursor, was transformed to (La,Ca)CrO3 and CaCrO4 above 80$0^{\circ}C$, which remained up to 110$0^{\circ}C$. However, only (La,Ca)CrO3 phase consisting of orthorhombic and intermediate rhombohedral polymorphs was observed after sintering at 125$0^{\circ}C$. The specimens sintered at 140$0^{\circ}C$ exhibited 98% of relative density and rather wide grain size distribution with average grain size of 3-4 ${\mu}{\textrm}{m}$. Densification and grain growth of the specimens observed above 125$0^{\circ}C$ were presumably attributed to liquid phase sintering resulted from melting of Ca3(CrO4)2 phase.

• 한국세라믹학회지
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• 제28권2호
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• pp.101-108
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• 1991

0.2 mo1% La doped BaTiO3 samples were prepared by a wet chemical process (Pechini process) and electrical conductivity were measured from annealing temperatures(800-110$0^{\circ}C$) to room temperature continuously. 2 probe I-V characteristics showed that Pt electrodes were non-ohmic below about 80$0^{\circ}C$ for Ladoped sample. I-V curves showed varistor behavior and breakdown voltages showed PTC-like behavior. AC complex impedance of 0.2 La and 0.05 Mn mo1% doped BaTiO3 samples with three different electrodes (electroless Ni, Pt, Ag electrodes) were measured with temperature variation. Complex impedance plots showed that the samples with electroless Ni electrodes have negligible electrode resistance. Samples with Ag or Pt paste electrodes showed large electrode resistance. PTC effect, which is defined as the ratio of maximum resistance to minimum resistance, was found to be less than 10 for 0.2 mo1% La doped dense sample however greater than 105 with codoping of 0.05 mo1% Mn and 0.2 mol% La.

• Bulletin of the Korean Chemical Society
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• 제20권8호
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• pp.893-896
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• 1999

Novel citric acid based Ti, Nb and Ta precursors that are highly stable in the presence of water were developed. No alkoxides of Ti, Nb and Ta were utilized in the preparation, instead much less moisture-sensitive metallic Ti, NbCl5 and TaCl5 were chosen as starting chemicals for Ti, Nb and Ta, respectively. The feasibility of these chemicals as precursors is demonstrated in the powder synthesis of BaTi4O9, Y3NbO7 and LiTaO3. The water-resistant Ti precursor was employed as a new source of water-soluble Ti in the amorphous citrate method, and phase pure BaTi4O9 in powdered form was successfully synthesized at 800 ？. The Pechini-type polymerizable complex method using the water-resistant Nb and Ta precursors was applied to the synthesis of Y3NbO7 and LiTaO3, and both the powder materials in their pure form were successfully synthesized at reduced tempera-tures, viz. 500-700 ？. The remarkable retardation of hydrolysis of these water-resistant precursors is explained in terms of the partial charge model theory.

• 한국세라믹학회지
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• 제41권4호
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• pp.284-288
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• 2004

Al$_2$O$_3$/ZrO$_2$복합체의 기계적 성질 향상을 위하여 분산되는 ZrO$_2$상을 Zr-Y-polyester의 고분자화(polyesterization) 공정(Pechin법)을 이용하여 알루미나 기지 중에 초미립으로 균질하게 분산시키기 위한 방안을 고찰하여 보았다. 일반적으로 공침법에 의해 제조되는 $Al_2$O$_3$/ZrO$_2$ 복합체의 경우 초기 ZrO$_2$입자의 크기가 매우 작아도 알루미나 내에 분산되는 ZrO$_2$입자가 소결시에 비교적 빠르게 성장 및 입자간의 응집이 발생하게 되며 이로 인해 분산의 불균일을 유발하여 미세하고 균질한 복합체를 얻기가 힘들다. 따라서 상용 이소결성 $\alpha$-Al$_2$O$_3$분말(Sumitomo.AES-11(0.5$mu extrm{m}$))에 ZrO(NO$_3$)$_2$와 Y(NO$_3$)$_3$를 citric acid/ethylene glycol과 혼합한 polyesterization시켜 $\alpha$-Al$_2$O$_3$입자 표면에 미세하고 균질하게 코팅 형태로 부착되도록 하였다. 이를 90$0^{\circ}C$에서 하소한 후 1450∼1$600^{\circ}C$의 온도에서 소결하여 미세한 ZrO$_2$입자가 매우 균질하게 분산된 $Al_2$O$_3$/ZrO$_2$ 복합체를 제조하였으며 이의 기계적 성질을 관찰하였다.