• Korean Journal of Materials Research
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• v.26 no.2
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• pp.90-94
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• 2016

In this study, to increase the strength and enhance the sintering property of $Al_2O_3$, $Y_2O_3$ and $La_2O_3$ were added; the effects of these additions on the sintering characteristics of $Al_2O_3$ were observed. Adding 1% of $Y_2O_3$ to $Al_2O_3$ repressed the development of abnormal particles and reduced the grain boundary migration of $Al_2O_3$, curbing pores to capture particles; as such, the material showed a fine microstructure. But, when over 2% of $Y_2O_3$ was added, the sintering property was reduced because of abnormal particle grain growth and pore formation in particles. Adding 1% of $Y_2O_3$ and $La_2O_3$ to $Al_2O_3$ led to the development of abnormal particles and formed pores in the particles; when over 3% of $La_2O_3$ was added, the sintering property was reduced because the shape of the $Al_2O_3$ particles changed to angled plates.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.325-325
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• 2007

The perovskites in the $LaAlO_3-BaZrO_3$ system (i.e., $(1-x)LaAlO_3-xBaZrO_3$ were fabricated by a solid state reaction and their dielectric properties were investigated. For the compositions of x=0.1~0.9, the mixture of $LaAlO_3$ with a rhombohedral structure and $BaZrO_3$ with a cubic was observed when the sintering was conducted at $1500^{\circ}C$, indicating that the solubility of constituent elements was very low and a narrow solid solution region might exist. The large difference of ionic radii between $La^{3+}$ ion (0.136nm, C.N.=12) and $Ba^{2+}$ ion (0.161nm) or $Al^{3+}$ ion (0.0535nm, C.N.=6) and $Zr^{4+}$ ion (0.072nm) might hinder the mutual substitution. Within the compositions of x=0~0.7, the dielectric constant of the mixture increased with the amount of $BaZrO_3$, i.e., x value, which was in good agreement with the logarithmic mixing rule (In $_{r,i}={\Sigma}v_iln\;_{r,i}$). The increase in $BaZrO_3$ doping decreased $Q{\times}f$ value significantly due to the low $Q{\times}f$ value of $BaZrO_3$ itself, a poor microstructure of the mixture with an increased grain boundary area per volume, and defects in the cation and oxygen sub-lattices which were respectively caused by the evaporation of barium during the sintering process and the substitution of Ba on La-site or Al on Zr-site.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.1
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• pp.14-19
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• 2013

We have successfully synthesized $Bi_{4-x}La_xTi_3O_{12}$ (x~2) having Aurivillius-type layered perovskite structure from exfoliated layered perovskite oxide of $K_2La_2Ti_3O_{10}$ with Ruddlesden-Popper structure. The reaction between the exfoliated lanthanum titanate nanosheets and BiOCl nanocrystal resulted in the formation of polycrystalline $Bi_{4-x}La_xTi_3O_{12}$ (x~2) after heating above $700^{\circ}C$. Colloidal suspension of the nanosheets could be obtained by intercalating ethylamine (EA) into the protonated lanthanum titanate, $H_2La_2Ti_3O_{10}$, derived from $K_2La_2Ti_3O_{10}$. Transmission electron microscopic (TEM) analysis show that the exfoliated lanthanium titanate nanosheets have a thickness of a few nano meters. According to X-ray diffraction (XRD) analysis, the exfoliated lanthanium titanate was found to be transformed into $Bi_{4-x}La_xTi_3O_{12}$ (x~2) after restacking with BiOCl and subsequent thermal treatment at > $700^{\circ}C$.

• Korean Journal of Materials Research
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• v.33 no.9
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• pp.367-371
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• 2023

In this study we examine variations in the structure of perovskite compounds of LaBa₂Cu₂O₉, LaBa2₂CaCu₃O₁₂ and LaBa₂Ca₂Cu₅O₁₅ synthesized using the solid state reaction method. The samples' compositions were assessed using X-ray fluorescence (XRF) analysis. The La: Ba: Ca: Cu ratios for samples LaBa₂Cu₂O₉, LaBa2₂CaCu₃O₁₂ and LaBa₂Ca₂Cu₅O₁₅ were found by XRF analysis to be around 1:2:0:2, 1:2:1:3, and 1:2:2:5, respectively. The samples' well-known structures were then analyzed using X-ray diffraction. The three samples largely consist of phases 1202, 1213, and 1225, with a trace quantity of an unknown secondary phase, based on the intensities and locations of the diffraction peaks. According to the measured parameters a, b, and c, every sample has a tetragonal symmetry structure. Each sample's mass density was observed to alter as the lead oxide content rose. Scanning electron microscope (SEM) images of the three phases revealed that different Ca-O and Cu-O layers can cause different grain sizes, characterized by elongated thin grains, without a preferred orientation.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.415-418
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• 2001

The I-V characteristics and its stability of ZPCCL-based ceramic varistors doped with La$_2$O$_3$in the range of 0.0~4.0 mol% were investigated. The density of ceramics was increased in the range of 4.7~5.8 g/cm$^3$ with increasing La$_2$O$_3$content. As La$_2$O$_3$content is increased, the varistor voltage was decreased in the range of 503.49-9.42 V/mm up to 2.0 mol%, whereas increasing La$_2$O$_3$content further caused it to increase. The ZPCCL-based varistors were characterized by nonlinearity, in which the nonlinear exponent is in the range of 3.05~82.43 and leakage current is in the range of 0.24-100.22 $\mu$A. Among ZPCCL-based varistors, 0.5 mol% added-varistors exhibited an excellent nonlinearity, in which the nonlinear exponent is 82.43 and the leakage current is 0.24 $\mu$A. Furthermore, they exhibited a high stability, in which the variation rate of the varistor voltage and the nonlinear exponent was -1.11% and -6.72%, respectively, under DC stress, such as (0.80 V$_{1mA}$9$0^{\circ}C$/12h)+(0.85 V$_{1mA}$115$^{\circ}C$//12h) +(0.90 V$_{1mA}$12$0^{\circ}C$//12h)+(0.95 V$_{1mA}$1$25^{\circ}C$//12h)+(0.95 V$_{1mA}$15$0^{\circ}C$//12h). Consequently, it was estimated that ZPCCL-based ceramics will be applied to development of Pr$_{6}$O$_{11}$ based ZnO varistors having a high performance.e.rformance.e.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.5
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• pp.197-202
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• 2021

Synthesis of Z-type hexaferrite Ba₃Co₂Fe₂₄O₄₁ (Ba₃Z) and Ba_1.5La_1.5Co₂Fe₂₄O₄₁ (Ba_1.5La_1.5Z) powders were tried using molten salt synthesis after primary calcination. Ba₃Z calcined at 1000℃ was formed with both M-type and Y-type hexaferrite, and then Z-type was obtained when sintered with molten salt at 1150℃ and 1200℃. In the case of Ba_1.5La_1.5Z calcined at 1000℃, however, M-type hexaferrite, CoFe₂O₄ (Spinel phase), and LaFeO₃ were synthesized. As a result, Z-type hexaferrite was not synthesized after sintering with molten salt. In addition, the aspect ratio of the particles decreased as the sintering temperature increased with molten salt synthesis. To obtain a single-phase Ba_1.5La_1.5Z with a high aspect ratio, it is expected the raw materials have to calcine below the temperature of a spinel phase formation before sintering with molten salt.

• The Korean Journal of Ceramics
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• v.6 no.4
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• pp.396-400
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• 2000

Dielectric and piezoelectric properties of Pb$_0.9$La$_0.1$TiO$_3$ ceramics were investigated as a function of grain size. Sintering atmosphere was controlled with changing the kind of atmospheric powder and its amount. It was confirmed that dielectric and piezoelectric of Pb$_0.9$La$_0.1$TiO$_3$ were strongly influenced by the sintering atmosphere. Relative dielectric constant of Pb$_0.9$La$_0.1$TiO$_3$ which was sintered in PbO-deficient atmosphere made by Pb$_0.9$La$_0.1$TiO$_3$ powder, increased with the grain size. However, the dielectric constant of the samples sintered in the PbO-sufficient atmosphere made by PbZrO$_3$ powder was slightly decreased with the grain size. Piezoelectric d$_33$ constant of Pb$_0.9$La$_0.1$TiO$_3$ also showed a different trend, depending on the sintering atmosphere. It was almost constant in the range of grain size of 1.3~2.3 $\mu$m when the samples were sintered in the PbO-sufficient atmosphere, while it intensively decreased with the grain size in the case of the PbO-deficient condition.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.3
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• pp.103-109
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• 2020

The effect of La₂O₃ addition on the crystalline phase, microstructure, and dielectric properties of BaTiO₃ has been studied as a function of the amounts of La₂O₃. 0.3 mol% TiO₂-excess BaTiO₃ powder was synthesized by solid-state reaction, and then the powder compacts with various amounts of La₂O₃ were sintered at 1250℃ for 2 hours. Room temperature XRD showed changes in the lattice parameters and a decrease of tetragonality (c/a) as the amounts of La₂O₃ increased. It can be explained that the phase transition from tetragonal to cubic phase occurred because La³⁺ replaced Ba²⁺ site, which increased the instability of the tetragonal phase. As La₂O₃ was added over 0.1 mol%, the critical driving force for growth (Δg_c) increased over maximum driving force (Δg_max). As the result, the grain size decreased with La₂O₃ addition. Dielectric constant decreased as the amounts of La₂O₃ increased, which was analyzed with crystal structure and microstructure.

• Journal of the Korean Ceramic Society
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• v.36 no.10
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• pp.1056-1061
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• 1999

Phase formation and oxygen ion conduction of La(Ba)Ga(Mg)O3-$\delta$ system was studied, BaLaGa3O7 and BaLaGaO4 formed as a secondary phase above the solubility limit of Ba2+ in La3+ sites. The oxygen ionic conductivity of La(Ba)Ga(Mg)O3-$\delta$ was 0.1 S/cm 80$0^{\circ}C$ The activation energy of the oxygen ion conduction was dependent on temperature. This value was higher at low temperature than at high temperature.

• Journal of the Korean Ceramic Society
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• v.36 no.1
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• pp.50-54
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• 1999

We have measured the x-ray photoemission spectroscopy of cation deficient La0.970Mn0.970O3 as a function of temperature. Detailed results on the chemical shifts and changes in Mn 2p and Lp 3d core levels due to variation of temperature have been obtained. The Mn 2p 3/2 and 1/2 main peaks and La 3d core spectrum shift to lower binding energy levels with increasing temperature. This XPS behavior is correlated with the strength of localization of Mn3+. The Jahn-Teller effect due to Mn3+ besides the conventional random potential effects is likely to localize charge carriers in La-.970Mn0.970O3.