共查询到20条相似文献,搜索用时 31 毫秒
1.
J. P. Guha 《Journal of the American Ceramic Society》1991,74(4):878-880
Ternary compounds in the system BaO—TiO2 —La2 O3 were prepared by the solid-state reaction technique at temperatures between 1300° and 1400°C using precursor oxides as the starting materials. In an alternative processing technique, BaTiO3 was reacted with appropriate proportions of prefabricated lanthanum titanates at 1350°C to obtain the compounds. Two compounds were identified in the TiO2 -rich region of the system. The X-ray powder diffraction pattern of a compound with a chemical composition BaLa2 Ti3 O10 (BaO·La2 O3 ·3TiO2 ) is indexed on the basis of an orthorhombic unit cell with a = 7.665 × 10−1 nm, b = 28.524 × 10−1 nm, and c = 3.876 × 10−1 nm. The other compound, which has a chemical composition Ba4 La8 Ti17 O50 (BaO·La2 O3 ·4.25TiO2 ) occurs in a narrow homogeneity range within the system. The X-ray powder diffraction pattern of the compound is indexed on the basis of an orthorhombic unit cell with a = 12.317 × 10−1 nm, b = 22.394 × 10−1 nm, and c = 3.881 × 10−1 nm. Both the compounds are compatible with BaTiO3 and form pseudobinary joins with BaTiO3 in the system BaO—TiO2 —La2 O3 . 相似文献
2.
Susumu Nishigaki Shinsuke Yano Hiroshi Kato Takami Hirai Toshio Nonomura 《Journal of the American Ceramic Society》1988,71(1):11-C-
Microwave ceramic resonators composed of BaO-TiO2 -WO3 were developed. The effect of WO3 addition on the system of BaO·xTiO2 ·(1+x)yWO3 (x=4 and 4.5, y=0 to 0.04) was studied. The ceramics of this system are composed of crystallines including Ba2 Ti9 O20 , BaTi4 O9 , BaWO4 , and TiO2 . At y=0.02, the BaO·4TiO2 ·0.1WO3 ceramic was found to have excellent microwave properties such as ε=35, Q=8400 at 6 GHz, and nearly 0 ppm/°C of τf . 相似文献
3.
T. Jaakola A. Uusimäki R. Rautioaho S. Leppävuori 《Journal of the American Ceramic Society》1986,69(10):234-C
Phase structures of two ceramics of Compositions BaNd2 Ti5 O14 and Ba3.75 Nd9.5 Ti18 O54 , both of which had earlier been reported to be single-phase materials, were investigated using electron microscopy and an electron probe microanalyzer. It was observed that the amount of secondary phases was much lower in ceramics prepared with the latter composition and that the composition of the matrix phase of both samples was near 4BaO·5 Nd2 O3 ·18TiO2 . These results indicate that only the composition Ba3.75 Nd9.5 Ti18 O54 is a single-phase composition. 相似文献
4.
Yong Ding Yoshinari Miura Akiyoshi Osaka 《Journal of the American Ceramic Society》1994,77(11):2905-2910
Improved polar ( c -axis) oriented growth of fresnoite (Ba2 TiSi2 O8 ) was observed for surface crystallization of a glass 33.3BaO· 16.7TiO2 · 50SiO2 (in mol%) due to ultrasonic surface treatment with an aqueous suspension of Ba2 TiSi2 O8 , and an oriented film more than 50 μm in thickness was prepared. The effect of ultrasonic treatment on the polar orientation depends on the suspending particles; of these, foreign particles of a phase other than the crystallizing Ba2 TiSi2 O8 give poorer efficiency than the Ba2 TiSi2 O8 particles. It is assumed that fresnoite has a tendency toward preferred polar growth on the glass, and seeding of a large number of fine particles through ultrasonic bombardment realizes the tendency. The polar-oriented growth kinetics of Ba2 TiSi2 O8 were also discussed. 相似文献
5.
Masahiro Nagae Takashi Atsumi Tetsuo Yoshio 《Journal of the American Ceramic Society》2006,89(3):1122-1124
Y-type Ba-hexaferrites (Ba2 Zn2 Fe12 O22 ), which have been identified as electromagnetic wave absorbers, were prepared by the glass–ceramic method. Glasses with the composition 0.1ZnO·0.9( x B2 O3 · y BaO·(1− x − y )Fe2 O3 ) were prepared, and the precipitation of Y-type Ba-hexaferrite from the glass matrix was investigated. Y-type Ba-hexaferrite were precipitated by heating glass specimens with roughly the composition 0.1ZnO·0.9(0.2B2 O3 ·0.5BaO·0.3Fe2 O3 ) at temperatures above about 1073 K. The lower temperature limit at which single-phase Y-type powder was obtained after leaching with a dilute HCl solution was about 1093 K. The low-temperature formation of Y-type Ba-hexaferrite was linked to the generation of a liquid phase. The shape of Y-type crystals depended strongly on the heating temperature and changed from a plate-like hexagon to a complex polyhedron with increasing heating temperature. 相似文献
6.
Jung-Kun Lee Jong-Sung Park Kug-Sun Hong Kyung-Hyun Ko Byung-Chan Lee 《Journal of the American Ceramic Society》2002,85(5):1173-1179
The role of liquid phase in the enhancement of the PTCR (positive temperature coefficient of resistance) effect in (Ba0.7 Sr0.3 )TiO3 (BST) with the addition of AST (4Al2 O3 · 9SiO2 · 3TiO2 ) is investigated in this paper. The AST–BST samples were characterized with optical microscopy, transmission electron microscopy, energy-dispersive spectroscopy, and impedance spectroscopy. Microscopic observations showed that slower cooling might facilitate the precipitation of the (Ba,Sr)TiO3 phase from the liquid phase on matrix grains since the amount of liquid phase was reduced with a decreasing cooling rate. Impedance spectroscopy indicated that this variation accompanied the change in the intrinsic properties of grain boundaries, which could not be explained by well-known oxidation effects. With the aid of a brick-layer model and high-resolution transmission electron microscopy (HRTEM), it appeared that the change in electrical characteristics of grain boundaries with decreasing cooling rate originated from the precipitation of (Ba,Sr)TiO3 . Finally, the effect of precipitated (Ba,Sr)TiO3 on the PTCR characteristics is discussed in terms of the acceptor-state density and the polarization state at grain boundaries. 相似文献
7.
Jenn-Ming Wu Ming-Chu Chang Pei-Chih Yao 《Journal of the American Ceramic Society》1990,73(6):1599-1605
The reaction sequence of 0.15(Ba0.95 Sr0.05 )O· 0.15Sm2 O3 · 0.7TiO2 ceramics during heating as well as the effects of calcination and sintering on microwave properties were investigated. Quantitative microscopic analysis was performed to obtain the volume fraction of the phases. It was found that the amount of second phase, especially TiO2 (rutile), greatly affected the temperature coefficient of resonant frequency of the ceramics. The higher the amount of TiO2 phase, the more positive or the less negative the temperature coefficient of resonant frequency. The temperature coefficient of BaO · Sm2 O3 · 5TiO2 was calculated using the logarithmic mixing rule to be −30 ppm/°C. The volume fractions of the phases varied with conditions of calcination and sintering. Therefore, by varying calcination and/or sintering temperature, the temperature coefficient of resonant frequency could be adjusted to nearly zero. 相似文献
8.
Hong-Yang Lu Wei-Lin Wang Wei-Hsing Tuan Ming-Hong Lin 《Journal of the American Ceramic Society》2004,87(10):1843-1847
The microstructure of vitrified kaolin ceramic tapes has been studied via scanning and transmission electron microscopy (SEM and TEM). The sintered samples contained crystalline phase of predominantly stoichiometric mullite (3Al2 O3 ·2SiO2 ), which consisted of high aspect ratio, acicular crystals that are often referred to as secondary mullite. These crystals were interlocked and embedded in an aluminosilicate glass matrix of inhomogeneous composition. The glass matrix contained an average of ∼3.63 wt% K as determined by energy-dispersive X-ray analysis (EDS), whose composition could be approximated to 5Al2 O3 ·16SiO2 ·0.1MgO·0.3K2 O·0.15TiO2 ·0.12Fe2 O3 . The acicular crystals have approximately the stoichiometric composition of Al2 O3 :SiO2 = 3:2. They have grown along a specific crystallographic orientation along the [001] axis. The crystal growth front exhibited facetting on the {110) planes with microfacetting on both the {100) and {010) planes. 相似文献
9.
Direct-Current Field Dependence of Dielectric Properties in Alumina-Doped Barium Strontium Titanate 总被引:7,自引:0,他引:7
Long Wu Yih-Chien Chen Cheng-Liang Huang Yi-Ping Chou Yuan-Tu Tsai 《Journal of the American Ceramic Society》2000,83(7):1713-1719
The dielectric properties of (Ba0.6 Sr0.4 )TiO3 and Al2 O3 -doped (Ba0.6 Sr0.4 )TiO3 have been characterized. The grain size of the specimen is maximum for (Ba0.6 Sr0.4 )TiO3 that has been doped with 1 wt% Al2 O3 . The density and the real part of the relative dielectric constant each decrease as the Al2 O3 content increases. The loss factor is minimum for (Ba0.6 Sr0.4 )TiO3 that has been doped with 2 wt% Al2 O3 . The dielectric constant of the specimens decreases as the applied dc field increases. The influence of the dc field on the loss factor is much less than that on the dielectric constant. The tunability is ∼24% for (Ba0.6 Sr0.4 )TiO3 that has been doped with 1 wt% Al2 O3 . 相似文献
10.
Dong-Wan Kim Kyung Hyun Ko Do-Kyun Kwon Kug Sun Hong 《Journal of the American Ceramic Society》2002,85(5):1169-1172
(1− x )ZnNb2 O6 · x TiO2 ceramics were prepared using both anatase and rutile forms of TiO2 . At a composition of x = 0.58, a mixture region of ixiolite (ZnTiNb2 O8 ) and rutile was observed and the temperature coefficient of resonant frequency (τf ) was ∼0 ppm/°C. We found that although ɛr and τf were comparable, the quality factor ( Q × f , Q ≈ 1/ tan δ, f = resonant frequency) of 0.42ZnNb2 O6 ·0.58TiO2 prepared from anatase and rutile was 6000 and 29 000, respectively. The origin of the difference in Q × f of both samples was investigated by measuring electrical conductivity and by analysis of the anatase–rutile phase transition. The anatase-derived sample had higher conductivity, which was related to the reduction of Ti4+ . It is suggested that the increase of dielectric loss originates from an increase in Ti3+ and oxygen vacancies due to an anatase–rutile phase transition. 相似文献
11.
TAKESHI KIKUCHT 《Journal of the American Ceramic Society》1977,60(3-4):148-150
The subsolidus phase equilibria in the system Bi2 O3 -TiO2 -Nb2 O5 at 1100°C were determined by solid-state reaction techniques and X-ray powder diffraction methods. The system was found to contain 4 ternary compounds, i.e. Bi3 TiNbO9 , Bi7 Ti4 NbO21 , a cubic pyrochlore solid solution having a compositional range of 3Bi2 O3 · x TiO2 (7– x )Nb2 O5 where x ranges from 2.3 to 6.75, and an unidentified phase, 4Bi2 O3 ·11TiO2 ·5Nb2 O5 . 相似文献
12.
Sea-Fue Wang Chiang-Chuang Chung Chai-Hui Wang Jinn P. Chu 《Journal of the American Ceramic Society》2002,85(6):1619-1621
Preparation of dense and phase-pure Ba2 Ti9 O20 is generally difficult using solid-state reaction, since there are several thermodynamically stable compounds in the vicinity of the desired composition and a curvature of Ba2 Ti9 O20 equilibrium phase boundary in the BaO–TiO2 system at high temperatures. In this study, the effects of B2 O3 on the densification, microstructural evolution, and phase stability of Ba2 Ti9 O20 were investigated. It was found that the densification of Ba2 Ti9 O20 sintered with B2 O3 was promoted by the transient liquid phase formed at 840°C. At sintering temperatures higher than 1100°C, the solid-state sintering became dominant because of the evaporation of B2 O3 . With the addition of 5 wt% B2 O3 , the ceramic yielded a pure Ba2 Ti9 O20 phase at sintering temperatures as low as 900°C, without any solid solution additive such as SnO2 or ZrO2 . The facilities of B2 O3 addition to the stability of Ba2 Ti9 O20 are apparently due to the eutectic liquid phase which accelerates the migration of reactant species. 相似文献
13.
H. M. O'BRYAN JR. J. THOMSON JR. J. K. PLOURDE 《Journal of the American Ceramic Society》1974,57(10):450-453
The dielectric properties of ceramics in the TiO2 -rich region of the BaO-TiO2 system were investigated. In the composition range between BaTi4 O9 and TiO2 , another compound, Ba2 Ti9 O20 , can be obtained when calcining and sintering conditions are controlled carefully. When dense and single-phase, this ceramic has excellent dielectric and physical properties. At 4 GHz, the dielectric K = 39.8, Q = 8000, and τ K (temperature coefficient of dielectric constant) =−24 ± 2 ppm/°C. 相似文献
14.
Soonil Lee Clive A. Randall Zi-Kui Liu 《Journal of the American Ceramic Society》2007,90(8):2589-2594
The ferroelectric phase transition behavior in BaTiO3 was investigated for various annealing times, temperatures, and Ba/Ti ratios by means of a differential scanning calorimeter. Coupling these observations with powder X-ray diffraction and transmission electron microscopy allowed new insights into the barium oxide (BaO)–titanium dioxide (TiO2 ) phase diagram. The transition temperature was varied systematically with the Ba/Ti ratio at annealing temperatures from 1200° to 1400°C in air. The transition temperature decreased with increasing concentrations of BaO and TiO2 partial Schottky defects, and showed a discontinuous change at the phase boundaries. Beyond the solubility region, two peritectoid reactions were confirmed and revised; first around 1150°C for Ba1.054 Ti0.946 O2.946 →Ba2 TiO4 +BaTiO3 and second 1250°C for BaTi2 O5 →Ba6 Ti17 O40 +BaTiO3 , respectively. All other regimes of the BaO–TiO2 were found to be consistent with the reported diagrams in the literature. 相似文献
15.
Modification of the microwave dielectric properties in Ba6−3 x Nd8+2 x Ti18 O54 ( x = 0.5) solid solutions by Bi/Sm cosubstitution for Nd was investigated. A large increase in the dielectric constant and near-zero temperature coefficient combined with high Qf values were obtained in modified Ba6−3 x Nd8+2 x Ti18 O54 solid solutions where an enlarged solid solution limit of Bi in Ba6−3 x Nd8+2 x Ti18 O54 was observed. Excellent microwave dielectric characteristics (ɛ= 105, Qf = 4110 GHz, and very low τf ) were achieved in the composition Ba6−3 x (Nd0.7 Bi0.18 Sm0.12 )8+2 x Ti18 O54 . 相似文献
16.
Phase relations in the system BaO-TiO2 from 67 to 100 mol% TiO2 were investigated at 1200° to 1450°C in O2 . Data were obtained by microstructural, X-ray, and thermal analyses. The existence of the stable compounds Ba6 Ti17 O40 , Ba4 Ti13 O30 , BaTi4 O9 , and Ba2 Ti9 O20 was confirmed. The compound BaTi2 O5 is unstable and either forms as a reaction intermediate below the solidus or crystallizes from the melt. The compounds Ba6 Ti17 O40 and Ba4 Ti13 O30 decompose in peritectic reactions, and BaTiO3 and Ba6 Ti17 O40 react to form a eutectic. Special conditions are required for the formation of Ba2 Ti9 O20 , which decomposes in a peritectoid reaction at 1420°C. The new phase diagram is presented. 相似文献
17.
Jin-Ho Choy Yang-Su Han Jeong-Ho Sohn Mitsuru Itoh 《Journal of the American Ceramic Society》1995,78(5):1169-1172
Microwave dielectrics of the TiO2 -rich BaO-TiO2 system (BaTi4 O9 and Ba2 Ti9 O20 ) were prepared by the citrate route. Pure and well-crystallized BaTi4 O9 and Ba2 Ti9 O20 particles of nanometer size (30–50 nm) could be obtained by thermal decomposition of citrate gel precursors. After sintering at 1200°–1350°C (for 2–10 h), dense compounds with >90% of theoretical density could be obtained. Dielectric properties of disk-shaped sintered specimens, in the microwave frequency region, were measured in the TE01δ mode. They were found to have excellent microwave characteristics: for BaTi4 O9 , εr = 36, Q = 4900 at 10.3 GHz, and τf = 16 ppm/°C; and for Ba2 Ti9 O20 , εr = 37, Q = 5300 at 10.7 GHz, and τf =−6.0 ppm/°C. 相似文献
18.
The dielectric properties, including the DC breakdown strength, of 1 mol% Nb5+ -doped BaTiO3 ceramics with different quantities of excess TiO2 have been investigated. The breakdown strength was found to decrease with increasing TiO2 content, but could not be readily explained by relative density and grain size effects. The decrease in the breakdown strength from a stoichiometric BaTiO3 composition to samples with excess TiO2 is believed to be due to the field enhancement effect (up to a factor of 1.40) at the BaTiO3 matrix because of the presence of a Ba6 Ti17 O40 second phase. The thermal expansion coefficient mismatch between the BaTiO3 matrix phase and the Ba6 Ti17 O40 phase may also result in a low breakdown strength. The dielectric properties of the pure Ba6 Ti17 O40 phase were also investigated and are reported herein. 相似文献
19.
Synthesis of Titanate Derivatives Using Ion-Exchange Reaction 总被引:3,自引:0,他引:3
Chul-Tae Lee Myeong-Heon Um Hidehiro Kumazawa 《Journal of the American Ceramic Society》2000,83(5):1098-1102
Two types of titanate derivatives, layered hydrous titanium dioxide (H2 Ti4 O9 · n H2 O) and potassium octatitanate (K2 Ti8 O17 ) with a tunnellike structure, were synthesized using an ion-exchange reaction. Fibrous potassium tetratitanate (K2 Ti4 O9 · n H2 O) was prepared by calcination of a mixture of K2 CO3 and TiO2 with a molar ratio of 2.8 at 1050°C for 3 h, followed by boiling-water treatment of the calcined products for 10 h. The material then was transformed to layered H2 Ti4 O9 · n H2 O through an exchange of K+ ions with H+ ions using HCl. K2 Ti8 O17 was formed by a thermal treatment of KHTi4 O9 · n H2 O. Pure KHTi4 O9 · n H2 O phase was effectively produced by a treatment of K2 Ti4 O9 with 0.005 M HCl solution for 30 min. Thermal treatment at 250°–500°C for 3 h resulted in formation of only K2 Ti8 O17 . 相似文献
20.
H. M. O'BRYAN W. H. GRODKIEWICZ J. L. BERNSTEIN 《Journal of the American Ceramic Society》1980,63(5-6):309-310
Ba2 Ti9 O20 crystallizes in the monoclinic system with α= l.4818(5) nm, b = 1.4283(6), and c = 0.7109(2) with β = 98.37°±0.07°. The most likely space group is P 21 / m , Z = 4 with a calculated density 4.58 g/cm3 . The powder pattern was indexed. The Ba2 Ti9 O20 crystals form as stellated groups when melts of BaCl2 + 20 to 50% TiO2 cool from 1275°C. 相似文献