• Title/Summary/Keyword: Pyrochlore Phase

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Characteristics of PZT/BT Multilayered thick film using Sol-gel Process (PZT/BT 이종 세라믹의 특성)

  • Lee, Sang-Heon;Lee, Young-Hie;Lee, Sung-Gap
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2005.07a
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    • pp.365-366
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    • 2005
  • PZT films are the most intensively investigated because PZT has advantages such as low processing temperature and large remnant values. In this paper, the microstructure and electric properties of $Pb(Zr_x,Ti_{(1-x)})O_3/BaTiO_3$ heterolayered thick films with Zr mole ranging from 30 to 70 % screen printed onto a alumina substrate were studied. $Pb(Zr_x,Ti_{(1-x)})O_3$ and $BaTiO_3$ powders were prepared by the sol-gel method. The $BaTiO_3$ powders were calcined at $700^{\circ}C$ for 2 hours. Structural properties of $Pb(Zr_x,Ti_{(1-x)})O_3/BaTiO_3$ multilayered thick films were investigated. As a result of the X-ray diffraction (XRD) analysis, $Pb(Zr_x,Ti_{(1-x)})O_3/BaTiO_3$ exhibited a perovskite polycrystalline phase without pyrochlore phase or any preferred orientation.

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Behavior of $Sb_2O_3$ in the Calcination Process of ZnO Varistor (ZnO 바리스터의 하소과정에서 $Sb_2O_3$의 거동)

  • Choi, Jin Seog;Mah, Jae Pyung;Paek, Su-Hyon
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.24 no.3
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    • pp.433-438
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    • 1987
  • The current-voltage characteristics of the ZnO varisor with and without Sb2O3 which were fabricated with the various calcination and sintering temperature were discussed by comparing the results of SEM-microstructures and X-ray diffraction analysis. The samples were calcined at the temperature up to 800\ulcorner for 2 hours and they were sintered at 1200-1300\ulcorner for 1 hour. Then, we applied the power up to dc 200 volt to the samples and measured the output current up to 100mA. The samples without Sb2O3 had lower nonlinear resistances at the all calcination and sintering temperatures due to the large grains because of not forming Spinel phase. The other samples contained Sb2O3 could form Pyrochlore and Spinel phases at the all calcination temperatures by X-ray diffraction phase analysis. We found that the Spinel phases which were formed at the calcination process inhibit growth of ZnO grain and give rise to the change of nonlinear resistances by SEM-microstructures. And we found that the base of ZnO grain growth control is strongly dependent on the behavior of Sb2O3 in calcination process.

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Dielectric and Pyroelectric Properties of Lead-Free Sodium Bismuth Titanate Thin Films Due to Excess Sodium and Bismuth Addition

  • Kang, Dong Heon;Kang, Yong Hee
    • Journal of the Microelectronics and Packaging Society
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    • v.20 no.4
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    • pp.25-30
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    • 2013
  • Pb-free ferroelectric $(Na_{0.5}Bi_{0.5})TiO_3$ (NBT) thin films were prepared by a modified sol-gel process. Their structural, dielectric and pyroelectric properties were investigated as a function of the excess Na/Bi ratio and the annealing temperature. In the case of thin films containing no excess Na and Bi, only partial amounts of the perovskite NBT were crystallized, where the films consisted mainly of the pyrochlore phase of $Bi_2Ti_2O_7$ for annealing conditions of $600{\sim}800^{\circ}C$. With increasing excess Na/Bi ratio, the proportion of the perovskite phase effectively increased due to the compensation of the volatile Na and Bi components. For a Na/Bi ratio of 2.0, the thin film with single NBT perovskite phase was obtained within XRD detection limit after annealing at $700^{\circ}C$ for 10 min and it showed the excellent dielectric properties, ${\varepsilon}r$ of ~550 and tan ${\delta}$ of 0.03. While these properties were degraded for Na/Bi ratio of 2.5 despite the existence of pure perovskite phase. The NBT thin film with Na/Bi ratio of 2.0 are also promising candidates for applications requiring pyroelectric devices because it was found to have pyroelectric coefficients of $1.3{\sim}7nC/cm^2K$ in the temperature range of $30{\sim}100^{\circ}C$.

Sintering and Electrical Properties of Cr-doped ZnO-Bi2O3-Sb2O3 (Cr을 첨가한 ZnO-Bi2O3-Sb2O3계의 소결과 전기적 특성)

  • Hong, Youn-Woo;Shin, Hyo-Soon;Yeo, Dong-Hun;Kim, Jin-Ho
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.23 no.12
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    • pp.942-948
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    • 2010
  • In this study we aims to examine the effects of 0.5 mol% $Cr_2O_3$ addition on the reaction, microstructure development, resultant electrical properties, and especially the bulk trap and interface state levels of ZnO-$Bi_2O_3-Sb_2O_3$ (Sb/Bi=0.5, 1.0, and 2.0) systems (ZBS). The samples were prepared by conventional ceramic process, and characterized by XRD, density, SEM, I-V, impedance and modulus spectroscopy (IS & MS) measurement. The sintering and electrical properties of Cr-doped ZBS (ZBSCr) systems were controlled by Sb/Bi ratio. Pyrochlore ($Zn_2Bi_3Sb_3O_{14}$) was decomposed more than $100^{\circ}C$ lowered on heating in ZBS (Sb/Bi=1.0) by Cr doping. The densification of ZBSCr (Sb/Bi=0.5) system was retarded to $800^{\circ}C$ by unknown Bi-rich phase produced at $700^{\circ}C$. Pyrochlore on cooling was reproduced in all systems. And $Zn_7Sb_2O_{12}$ spinel ($\alpha$-polymorph) and $\delta-Bi_2O_3$ phase were formed by Cr doping. In ZBSCr, the varistor characteristics were not improved drastically (non-linear coefficient $\alpha$ = 7~12) and independent on microstructure according to Sb/Bi ratio. Doping of $Cr_2O_3$ to ZBS seemed to form $Zn_i^{..}$(0.16 eV) and $V^{\bullet}_o$ (0.33 eV) as dominant defects. From IS & MS, especially the grain boundaries of Sb/Bi=0.5 systems were divided into two types, i.e. sensitive to oxygen and thus electrically active one (1.1 eV) and electrically inactive intergranular one (0.95 eV) with temperature.

Study on Synthesis of Pyrochlore in Gd-Ti-O and Gd-Zr-O Systems (Gd-Ti-O계 및 Gd-Zr-O 계에서의 파이로클로어 합성연구)

  • ;;;S.V. Yudintsev
    • Economic and Environmental Geology
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    • v.37 no.3
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    • pp.303-309
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    • 2004
  • Pyrochlores were known as promising materials for the immobilization of radioactive actinide. Accordingly, we synthesized pyrochlores with Gd$_2$Ti$_2$$O_7$ and Gd$_2$Zr$_2$$O_7$compositions by sintering method, and studied its properties and phase relations in Gd-Ti-O and Gd-Zr-O system. The mixed powders were pressed into pellets under 200-400 kgf/cm$^2$ at room temperature. and then sintered at 1000-1$600^{\circ}C$ for 0.5-40 hours. The synthesized samples were analyzed and were identified with XRD and SEM/EDS analyses. The optimal synthetic conditions of pyrochlores with Gd$_2$Ti$_2$$O_7$composition were at 140$0^{\circ}C$/0.5hrs, 130$0^{\circ}C$/3hrs and 120$0^{\circ}C$/20hrs. Its chemical composition was $Gd_{2.0-2.1}$$Ti_{1.9-2.0}$$O_7$ and similar to the stoichiometric composition without any relationship in temperature and atmosphere. The optimal synthetic conditions of pyrochlores with $Gd_{2}$$Zr_{2}$$O_7$composition were at 155$0^{\circ}C$/40hrs and 1$600^{\circ}C$/30hrs. The compositions of pyrochlore synthesized from these optimal conditions were irregular with $Gd_{1.5-2.4}$$Zr_{1.7-2.4}$$O_7$. Such heterogeneity indicates that the reaction rate of pyrochlore with Gd$_2$Zr$_2$$O_7$composition is very low, and then its equilibrium state could not be attained even for 40 hours which was the longest sintering time in this research.

Phase Formation and Thermo-physical Properties of Lanthanum/Gadolinium Zirconate with Reduced Rare-earth Contents for Thermal Barrier Coatings (열차폐코팅을 위한 희토류가 저감된 란타눔/가돌리늄 지르코네이트의 상형성 및 열물성)

  • Lee, Sujin;Kwon, Chang-Sup;Lee, Sung-Min;Oh, Yoon-Suk;Kim, Hyung-Tae;Nahm, Sahn;Kim, Seongwon
    • Journal of Powder Materials
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    • v.22 no.6
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    • pp.420-425
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    • 2015
  • Rare-earth zirconates, such as lanthanum zirconates and gadolinium zirconates, have been intensively investigated due to their excellent properties of low thermal conductivity as well as chemical stability at high temperature, which can make these materials ones of the most promising candidates for next-generation thermal barrier coating applications. In this study, three compositions, lanthanum/gadolinium zirconates with reduced rare-earth contents from stoichiometric $RE_2Zr_2O_7$ compositions, are fabricated via solid state reaction as well as sintering at $1600^{\circ}C$ for 4 hrs. The phase formation, microstructure, and thermo-physical properties of three oxide ceramics are examined. In particular, each oxide ceramics exhibits composite structures between pyrochlore and fluorite phases. The potential of lanthanum/gadolinium zirconate ceramics for TBC applications is also discussed.

Fabrication and Characterization of Ceramics and Thermal Barrier Coatings of Lanthanum Zirconate with Reduced Rare-earth Contents in the La2O2-ZrO2 System (희토류 저감형 란타눔 지르코네이트(La2O2-ZrO2계) 세라믹스와 열차폐코팅의 제조 및 특성평가)

  • Kwon, Chang-Sup;Lee, Sujin;Lee, Sung-Min;Oh, Yoon-Suk;Kim, Hyung-Tae;Jang, Byung-Koog;Kim, Seongwon
    • Journal of Powder Materials
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    • v.22 no.6
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    • pp.413-419
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    • 2015
  • Lanthanum zirconate, $La_2Zr_2O_7$, is one of the most promising candidates for next-generation thermal barrier coating (TBC) applications in high efficient gas turbines due to its low thermal conductivity and chemical stability at high temperature. In this study, bulk specimens and thermal barrier coatings are fabricated via a variety of sintering processes as well as suspension plasma spray in lanthanum zirconates with reduced rare-earth contents. The phase formation, microstructure, and thermo-physical properties of these oxide ceramics and coatings are examined. In particular, lanthanum zirconates with reduced rare-earth contents in a $La_2Zr_2O_7-4YSZ$ composite system exhibit a single phase of fluorite or pyrochlore after fabricated by suspension plasma spray or spark plasma sintering. The potential of lanthanum zirconate ceramics for TBC applications is also discussed.

Characteristics of Bulk and Coating in Gd2-xZr2+xO7+0.5x(x = 0.0, 0.5, 1.0) System for Thermal Barrier Coatings

  • Kim, Sun-Joo;Lee, Sung-Min;Oh, Yoon-Suk;Kim, Hyung-Tae;Jang, Byung-Koog;Kim, Seongwon
    • Journal of the Korean Ceramic Society
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    • v.53 no.6
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    • pp.652-658
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    • 2016
  • Gadolinium zirconate, $Gd_2Zr_2O_7$, is one of the most versatile oxides among the new thermal-barrier-coating (TBC) materials for replacing conventional yttira-stabilized zirconia (YSZ). $Gd_2Zr_2O_7$ exhibits excellent properties, such as low thermal conductivity, high thermal expansion coefficient comparable with that of YSZ, and chemical stability at high temperature. In this study, bulk and coating specimens with $Gd_{2-x}Zr_{2+x}O_{7+0.5x}$ (x = 0.0, 0.5, 1.0) compositions were fabricated in order to examine the characteristics of this gadolinium zirconate system with different Gd content for TBC applications. Especially, coatings with $Gd_{2-x}Zr_{2+x}O_{7+0.5x}$ (x = 0.0, 0.5, 1.0) compositions were produced by suspension plasma spray (SPS) with suspension of raw powder mixtures prepared by planetary milling followed by ball milling. Phase formation, microstructure, and thermal diffusivity were characterized for both sintered and coated specimens. Single phase materials with pyrochlore or fluorite were fabricated by normal sintering as well as SPS coating. In particular, coated specimens showed vertically-separated columnar microstructures with thickness of $400{\sim}600{\mu}m$.

The Characteristics of PZ-PT PMN Piezoelectric Ceramics for Application to High Power Device (고출력 압전 디바이스 응용을 위한 PZ-PT-PMN계 압전 세라믹의 특성)

  • ;洪鍾國
    • The Transactions of the Korean Institute of Electrical Engineers C
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    • v.49 no.3
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    • pp.156-156
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    • 2000
  • The piezoelectric properties and the doping effect for $0.95Pb(Zr_xTi_{l-x})O_3+0.O5Pb(Mn_{1/3}Nb_{2/3})O_3$compositions were studied. Also, the heat generation and the change of electromechanical characteristics, the important problem in practical usage, were investigated under high electric field driving. As a experiment results under low electric field, the value of $k_p$ and ${\varepsilon}_{33}^T$ were maximized, but $Q_m$ was minimized $(k_p=0.57, Q_m=1550)$ in the composition of x=0.51. In order to increase the values of $Q_m$, $Nb_2O_5$ was used as a dopant. As the result of that, the grain size was suppressed and the uniformity of grain was improved. Also, the values of $k_p$ decreased, and the values of $Q_m$ increased with doping concentration of $Nb_2O_5$ . As a experiment results under high electric field driving, when vibration velocity was ower than 0.6[m/s], the temperature increase was 20[℃], and the change ratio of mechanical quality factor was less than 10[%]. So, its electromechanical characteristics was very stable. Conclusively, piezoelectric ceramic composition investigated at this paper is suitable for application to high power piezoelectric devices.

Structural and ferroelectric characteristics of sol-gel $Pb(Zr_{1-x}Ti_x)O_3$ thin films according to the sintering conditions and Zr/Ti mol% (소성 조건과 Zr/Ti 몰비에 따른 졸겔 $Pb(Zr_{1-x}Ti_x)O_3$ 박막의 구조 및 강유전 특성)

  • 김준한;윤현상;박정흠;장낙원;박창엽
    • Electrical & Electronic Materials
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    • v.9 no.8
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    • pp.836-850
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    • 1996
  • In this study, we have analyzed structural analysis and measured ferroelectric characteristics of PZT thin films prepared by sol gel process with different sintering conditions and different Zr/Ti mot%. When the Zr mot% of PZT thin film was increased, it was found that the remanent. polarization and coercive field were decreased and increased, respectively. Also, the maxium dielectric constant of PZT(50/50) thin film was 786.8. We got double hysteresis(anti-fcrroelectric) curve from PbZrO$_{3}$ thin film. As heating rate goes up, pyrochlore phase of PZT thin film was decreased and dielectric and ferroelectric characteristics were improved. As a result of variation of sintering temperature and time 500.deg. C-800.deg. C and 5 sec.-8 hours, respectively, we got optimal sintering temperature and time. The optimium sintering temperature and time of conventional furnace method and rapid thermal processing method were 650.deg. C-700.deg. C for 30-60 minutes and 700.deg. C/20 seconds-2 minutes, respectively.

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