• 한국분말재료학회지
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• 제19권6호
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• pp.429-434
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• 2012

With increase in operating temperature of gas turbine for higher efficiency, it is necessary to find new materials of TBC for replacement of YSZ. Among candidate materials for future TBCs, zirconate-based oxides with pyrochlore and fluorite are prevailing ones. In this study, phase structure and thermal conductivities of $(La_{1-x}Gd_x)_2Zr_2O_7$ oxide system are investigated. $(La_{1-x}Gd_x)_2Zr_2O_7$ system are comprised by selecting $La^{3+}/Gd^{3+}$ as A-site ions and $Zr^{4+}$ as B-site ion in $A_2B_2O_7$ pyrochlore structures. With powder mixture from each oxide, $(La_{1-x}Gd_x)_2Zr_2O_7$ oxides are fabricated via solid-state reaction at $1600^{\circ}C$. Either pyrochlore or fluorite or mixture of both appears after heat treatment. For the developed phases along $(La_{1-x}Gd_x)_2Zr_2O_7$ compositions, thermal conductivities are examined, with which the potential of $(La_{1-x}Gd_x)_2Zr_2O_7$ compositions for TBC application is also discussed.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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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.

• Applied Science and Convergence Technology
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• 제26권4호
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• pp.70-73
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• 2017

The dielectric constant and loss of poling/non-poling was measured in the $Pb_{1-3x/2}La_x[(Mg_{1/3}Ta_{2/3})_{0.66}Zr_{0.34}]O_3$ samples. The addition of $La^{3+}$ to the $Pb_{1-3x/2}La_x[(Mg_{1/3}Ta_{2/3})_{0.66}Zr_{0.34}]O_3$ did not cause a large change in grain size. But the addition of $La^{3+}$ did show transition temperature, which shifted toward low temperature in the $Pb[(Mg_{1/3}Ta_{2/3})Zr]O_3$ systems. In addition, the dielectric and pyroelectric properties (${\varepsilon}{\sim}20000$, $p{\sim}0.03C/m^2K$) of this system using $La^{3+}$ have been greatly improved. Pyroelectrics $Pb_{0.97}La_{0.02}(Mg_{1/3}Ta_{2/3})_{0.66}Zr_{0.34}]O_3$ system was found to have a relatively high ferroelectric FOMs ($F_V{\sim}0.035m^2/C$, $F_D{\sim}0.52{\times}10^{-4}Pa^{-1/2}$) at room temperature. Spontaneous polarization showed a value of $0.27{\sim}0.35C/m^2$ in the composition added to $La^{3+}$. The piezoelectric constant ($d_{33}=350{\sim}490pC/N$) and electromechanical coupling factor ($k_P=0.25{\sim}0.35$) are obtained in $Pb_{1-3x/2}La_x[(Mg_{1/3}Ta_{2/3})_{0.66}Zr_{0.34}]O_3$ compositions with $La^{3+}$ dopant.

• 한국세라믹학회지
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• 제31권5호
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• pp.513-519
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• 1994

In-situ 반응에 의하여 형성된 La-$\beta$-aluminate (LaAl11O18)로 강화된 알루미나 복합체에 정방정 ZrO2를 첨가하여 알루미나 복합체를 제조하였다. 사용된 분말 혼합체의 조성은 (100-x)[88 Al2O3+(La2O3+11 Al2O3)]+x vol% ZrO2였으며, x는 0부터 40까지 변화시켰다. 열간가압형성에 의하여 얻어진 치밀한 소결체는 1200MPa의 곡강도값을 나타내었다. 이러한 높은 곡강도값은 첨가한 ZrO2 입자와 기존의 La-$\beta$-aluminate platelets의 기지 입자에 대한 입성장 억제 효과와 ZrO2의 응력유기 상변태 효과로부터 기인하였다. 상기 복합체의 파괴 인성도 역시 8.58.5 MPa.m1/2까지 증가하였는데, 이러한 파괴인성의 증가는 ZrO2의 상변태 강화와 미세균열 강화, 그리고 La-$\beta$-aluminate와 ZrO2 입자의 균열 deflection과 bridging의 효과로 설명되어질 수 있다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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• pp.258-258
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• 2008

Among several available high-k dielectrics the lanthanum zirconium oxide ($LaZrO_x$) system is very attractive as a buffer insulating layer. Because both lanthanum and zirconium atoms, the constituents of the $LaZrO_x$ thin film, have been considered to be thermally stable in contact with Si. The $LaZrO_x$ films were deposited by a sol-gel method. After the deposition, The $LaZrO_x$ films were crystallized at $750^{\circ}C$ for 30 minutes in $O_2$ ambient. PVDF-TrFE films were deposited on these $LaZrO_x$/Si structures using a sol-gel technique. The sol-gel solution was spin-coated on $LaZrO_x$/Si structures at 500 rpm for 5 sec and 2500 rpm for 15 sec. The deposited layer was dried at $165^{\circ}C$ for 30 min in air on a hot-plate. Then, we deposited Au electrode on PVDF-TrFE films using thermal evaporation.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 추계학술대회 논문집
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• pp.171-172
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• 2007

We fabricated the metal-ferroelectric-insulator-semiconductor filed-effect transistors (MFIS-FETs) using the $(Bi,La)_4Ti_3O_{12}\;and\;LaZrO_x$ thin films. The $LaZrO_x$ thin film had a equivalent oxide thickness (EOT) value of 8.7 nm. From the capacitance-voltage (C-V) measurements for an Au/$(Bi,La)_4Ti_3O_{12}/LaZrO_x$/Si MFIS capacitor, a hysteric shift with a clockwise direction was observed and the memory window width was about 1.4 V for the bias voltage sweeping of ${\pm}9V$. From drain current-gate voltage $(I_D-V_G)$ characteristics of the fabricated Fe-FETs, the obtained threshold voltage shift (memory window) was about 1 V due to ferroelectric nature of BLT film. The drain current-drain voltage $(I_D-V_D)$ characteristics of the fabricated Fe-FETs showed typical n-channel FETs current-voltage characteristics.

• 한국분말재료학회지
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• 제18권6호
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• pp.568-574
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• 2011

As operating temperatures of engines or turbines continually increase for higher efficiency, significant amounts of researches have been focused on finding new materials, which would be alternatives to conventional yttria-stabilized zirconia (YSZ) for thermal barrier coatings (TBCs). In this study, phase evolution and thermo-physical properties of $La_2(Zr_{1-x}Hf_x)_2O_7$ pyrochlore systems are investigated for TBC applications. $La_2(Zr_{1-x}Hf_x)_2O_7$ systems are comprised by selecting $La^{3+}$ as A-site ions and $Zr^{4+}/Hf^{4+}$ as B-site ions in $A_2B_2O_7$ pyrochlore structures. For the developed phases in $La_2(Zr_{1-x}Hf_x)_2O_7$ compositions, thermo-physical properties such as thermal conductivity, thermal expansion coefficient are examined. The potential of these $La_2(Zr_{1-x}Hf_x)_2O_7$ compositions for TBC application is also discussed.

• 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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• 제17권2호
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• pp.80-88
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• 1980

The sintering phenomena and piezoelectric properties of PZT ceramics of composition $Pb(Zr_{0.54} Ti_{0.46})O_3$ were investigated when a small quantity of $La_2O_3$ , $LaMnO_3$, $LaCrO_3$ were added. The unwanted chemical composition change in PZT during sinterin porces du to PbO evaporation poses a severe problem in PZt manufacturinig. It is observed tat an addition of small amount of $LaMnO_3$ to PZT markedly decreases the evaporation of PbO during sintering . The green compact of (1-x) PZT.xLaMnO3(x=0.02~0.10) could be sintered of under O2 atmosphere alone with no significant loss of PbO. The planar coupling factor kp of the sintered $0.98Pb(Zr_{0.54} Ti_{0.46})O_{3.0.02}LaMnO}3$ is similar to that of commercial PZT 6A. Microstructure investigation shows that part of sintering process of $Pb(Zr, Ti)O_3$.$LaMnO_3$ system progresses via liquid phase sintering. It is believed that the evaporation of PbO in PZT sintering is restricted by the addition of $LaMnO_3$ due to the above phenomena. Furthermore the solid solution of $LaMnO_3$ in PZT causes diffuses phase transition.

• 한국표면공학회지
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• 제49권6호
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• pp.604-611
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• 2016

In order to comply with demand for high efficient gas turbines operating at higher temperatures, considerable amounts of research efforts have been performed with searching for the next-generation thermal barrier coatings (TBCs) with respect to coating materials as well as processing methods. In this study, thermal barrier coatings in the $(La_{1-x}Gd_x)_2Zr_2O_7$ system, which is one of the most versatile materials replacing yttria-stabilized zirconia (YSZ), are fabricated by suspension plasma spray with suspension made of synthesized powders via solidstate reaction. Dense, $100{\sim}400{\mu}m$ thick coatings of fluorite-phase zirconate with moderate amount of segmented microstructures are obtained by using suspension plasma spray. Phase formation and thermal diffusivity are characterized with coating compositions. The feasibility of $(La_{1-x}Gd_x)_2Zr_2O_7$ coatings for TBC applications is also discussed.