• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.618-620
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• 2002

The sintering and dielectric characteristics of $(1-x)Al_2O_3-xLa_2O_3$ ceramics (x=0.2, 0.4, 0.5, 0.6, 0.8, 1.0) were investigated. The sample of x=0.6 composition showed a largest density$(6.5g/cm^3)$ in the all samples and its grain were very uniform. The dielectric constant of the samples linearly increased from 9 to 17 up to x=0.6 with a increasing of x. The temperature coefficient of resonance frequency for the samples showed a positive value at x=0.2 and a negative value at x>0.4.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.6
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• pp.215-219
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• 2020

After the specimen of A-site defect double Perovskite La1/3TaO3 single crystal was manufactured, the dielectric properties have been studied between the temperature range of 10 and 800 K. Under 500 K, a paraelectric behavior has been shown, and above 550 K, a dielectric anomaly and a thermal history of dielectric constant has been shown. An activation energy by measurement of ac-conductivity has been the largest with 1.83 eV in the areas below 560 K, 0.35 eV in the areas of 560~690 K, and 0.28 eV in the areas of high temperature above 690 K. From these results, it is assumed that in the areas below 500 K, La3+-ion and vacancy-site are arranged in disorder to maintain a paraelectric phase. And in the areas near 560 K with the highest activation energy, a dielectric anomaly is attributes to rearrangement of La3+-ion due to conduction to vacancy-site or jumping.

• Journal of the Korean Ceramic Society
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• v.32 no.3
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• pp.378-384
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• 1995

Effects of $La_2O_3$, $MnO_2$ on the dielectric and piezoelectric properties of $0.02Pb(Y_{2/3}W_{1/3}O_3-0.98Pb(Zr_{0.52}Ti_{0.48})O_3$ system were investigated. The addition of La2O3 to the system enhanced electromechanical coupling factor (kp), piezoelectric constant (d33), but hardly changed mechanical quality factor (Qm). On the other hand, the addition of $MnO_2$ increased Qm significantly, but did not degrade kp and d33 so much. The piezoelectric properties of $0.02Pb(Y_{2/3}W_{1/3}O_3-0.98Pb(Zr_{0.52}Ti_{0.48})O_3$ containing 0.1wt% $La_2O_3$, 0.4wt% $MnO_2$ were very good and kp, d33, Qm were 55%, 350$\times$10-12C/N, 780, respectively. The size of the grains was proportional to the change of c/a (tetragonality) ratio caused by the addition of $La_2O_3$ and $MnO_2$, and dielectric, piezoelectric properties were sensitive to the amountof pyrochrole phase.

• Bulletin of the Korean Chemical Society
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• v.22 no.3
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• pp.298-302
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• 2001

A site preference of niobium atom in Rb2-xLa2Ti3-xNbxO10 (0.0 $\leq$ x $\leq1.0)$ and RbLa2-xCaxTi2-xNb1+xO10 (0.0 $\leq$ x $\leq2.0)$, which are the solid-solutions between Rb2La2Ti3O10 and RbCa2Nb3O10, has been investigated by Raman spectroscopy. The Raman spectra of Rb2-xLa2Ti3-xNbxO10 (0.0 $\leq$ x $\leq1.0)$ gave an evidence that niobium atoms substituted for titanium atoms preferably occupy the highly distorted outer octahedral sites rather than the central ones in triple-octahedral perovskite layers. In contrast, the Raman spectra of RbLa2-xCaxTi2-xNb1+xO10 (0.0 $\leq$ x $\leq2.0)$ showed no clear information for the cationic arrangement in perovskite slabs. This difference indicated that a site preference of niobium atoms is observed only when the linear Rb-O-Ti linkage can be replaced by much stronger terminal Nb-O bond with double bond character. From comparison with the Raman spectroscopic behavior of CsLa2-xA’xTi2-xNb1+xO10 (A’ = Ca and Ba; 0.0 $\leqx\leq2.0)$, it is also proposed that a local difference in arrangement of interlayer atoms causes a significantly different solid acidity and photocatalytic activity of the layered perovskite oxides, despite their crystallographically similar structures.

• Journal of Magnetics
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• v.7 no.1
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• pp.18-20
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• 2002

The charge structures of (LSMO) and of the combined system $(La_{ 0.6}Sr_{0.4}FeO_3$(LSMO) and of the combined system (La_{0.6}Sr_{0.4}MnO_3)_{0.7}(La_{0.6}Sr_{0.4}/FeO_3)_{0.3}$are investigated by using M$\ddot{o}$ssbauer spectroscopy. The antiferromagnetically ordered $(La_{0.6}Sr_{0.4}FeO_3$(LSFO) has possible charges of Fe^{3+} and Fe^{4+}$, which include a low-spin $Fe^{4+}$ state at and above 230 K. The temperature dependences of the M$\ddot{o}$ssbauer spectra for the $(La_{ 0.6}Sr_{0.4}FeO_3$ system and for the combined $(LSMO)_{ 0.7}(LSFO)_{0.3}$ system are fitted as three sets of Zeeman patterns corresponding to $Fe^{3+}$ and $Fe^{4+} below 230 K. At and above 230 K, the fitted M$\ddot{o}$ssbauer spectra for the combined system are the same in all temperature ranges. Above 230 K, $(La_{0.6}Sr_{0.4}FeO_3$ spectrum consists of two sets of six Lorentzians for $Fe^{3+}$ and one line for low spin $Fe^{4+}$. It is worth noting that large fields are induced in the combined system.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.6
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• pp.249-253
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• 2010

After the specimen of A-site defect perovskite $La_{1/3}NbO_3$ single crystal was manufactured, the dielectric properties were studied between the temperature range of 10 and 800 K. The dielectric anomaly appeared at 50 K and 650 K, and, at about 650 K, the thermal hysteresis of dielectric constant was shown. The ac-conductivity of bulk showed the lowest activation energy of 0.43 eV at 560~690 K. Based on the results, it is assumed that the dielectric anomaly at 50K and 650 K was due to the antiparallel shift of $Nb^{5+}$-ion and the rearrangement of $Nb^{3+}$-ion, respectively.

• Journal of the Korean Ceramic Society
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• v.34 no.6
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• pp.629-635
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• 1997

The effects of the annealing atmospheres(O2, N2) and sintering additives that Bi2O3 is a major composition on the microwave dielectric and sintering propertie of (1-x)CaTiO3-xLaAlO3 system were investigated. The annealing atmospheres and the increase of annealing time after sintering did not affect the relative dielectric constant($\varepsilon$r) and temperature coefficient of resonant frequency($\tau$f) of (1-x)CaTiO3-xLaAlO3 system. However, the Q.f0 values of (1-x)CaTiO3-xLaAlO3 were very sensitive to annealing atmospheres. As the annealing time increased under O2 atmosphere the Q.f0 values of (1-x)CaTiO3-xLaAlO3 enhanced untill 10 hrs in 0.3$\leq$x$\leq$0.6 region, but degraded over that time. The increasing rate of Q.f0 value increased wth increasing x. On the other hand, as the annealing time increased under N2 atmosphere the Q.f0 values were constant in x$\leq$0.6 region, increased gradually in x$\geq$0.7 region. When 0.97Bi2O3-0.03Al2O3 and 0.76Bi2O3-0.24NiO of 3wt% as sintering additives were added to (Ca0.5La0.5) (Ti0.5Al0.5)O3 (x=0.5) the sintering temperature of 1$600^{\circ}C$ was lowered to 140$0^{\circ}C$, and the relative dielectric constant($\varepsilon$r) and temperature coefficient of resonant frequency($\tau$f) were not nearly changed. The addition of 0.97Bi2O3-0.03Al2O3 and 0.76Bi2O3-0.24NiO of 3wt% to (Ca0.5La0.5)(Ti0.5Al0.5)O3 made the Q.f0 values to be lower about 15% and 34%, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1992.11a
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• pp.31-33
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• 1992

This paper is studies the addition effects of $La_2O_3$ on the magnetic properties of Sr ferrite. Compositions were chosen according to the formula $[SrO{\cdot}nFe_2O_3]_{100-x}(La_2O_3)_x$. where n was varied between 5.8~6.1 and x between 0~3. The composition of the best value $(BH)_{max}$=1.48MGOe was n=6(stoichiometric composition) and x=2 at $La_2O_3$ addition. This value was higher than that of ordinary isotropic strontium ferrite.

• Transactions of the Korean hydrogen and new energy society
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• v.29 no.5
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• pp.419-426
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• 2018

$Ni-La_2O_3-Ce_{0.8}Zr_{0.2}O_2$ catalysts with various $La_2O_3$ loading were investigated for hydrogen production from steam reforming of methane (SRM). The $La_2O_3$ loading influenced the physicochemical properties of $Ni-La_2O_3-Ce_{0.8}Zr_{0.2}O_2$ catalysts such as BET surface area, Ni dispersion, Ni size and reducibility. Among the prepared catalysts, $Ni-70La_2O_3-Ce_{0.8}Zr_{0.2}O_2$ catalyst showed the highest activity and stability at a very high gas hourly space velocity (GHSV) of $932,556h^{-1}$. This is mainly due to high Ni dispersion, small Ni size and high reducibility.

• Korean Journal of Materials Research
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• v.10 no.6
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• pp.437-444
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• 2000

We investigated the effect of substrate temperature, chemical composition and post-deposition heat-treatment on the crystal structure and electrical transport of $La_{1-x}Sr_xMnO_{3-{\delta}}$(0.19${\leq}x{\leq}$0.31) thin films. As-prepared $La_{1-x}Sr_xMnO_{3-{\delta}}$ films grown at $500^{\circ}C$ by sputter techniques were found to have the pseudo-tetragonal system(a/c=0.97) and a highly preferential <001> orientation. The films were changed to be of the cubic system by post-deposition annealing at around $900^{\circ}C$. A main target of $La_{0.67}Sr_{0.33}MnO_3$ as well as auxliary targets of $La_{0.3}Sr_{0.7}MnO_3$ ceramics were co-sputtered to control the chemical composition of the film. The Sr content(x) of the film ranged from 0.19 to 0.31, depending on the number of the auxiliary target. When x increased from 0.19 to 0.31, the electrical resistivity of the film decreased and the transition temperature between metal and semiconductor shifted to higher temperature. With a magnetic field of 0.18 T, the magneto-resistance ratio (MR(%) = (${\rho}_o-{\rho}_H/{\rho}_H$) of the $La_{0.69}Sr_{0.31}MnO_3$ thin film was about 390%.