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1.
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
2.
Yi Li Xiang Ming Chen † Ni Qin YaoWu Zeng 《Journal of the American Ceramic Society》2005,88(2):481-484
Tin (Sn) substitution for titanium (Ti) was investigated in Ba6−3 x Nd8+2 x Ti18 O54 ( x =1/2, 2/3, and 3/4) ceramics. A small amount ( z <0.1) of Sn substitution resulted in Ba6−3 x Nd8+2 x (Ti1− z Sn z )18 O54 solid solutions, and some secondary phases were observed with increasing Sn content. A small amount of Sn substitution improved the Q f value significantly, while, due to the formation of secondary phases, the Q f value degraded sharply for larger Sn content. The relative dielectric constant (ɛr ) decreased with increasing Sn-content, while the temperature coefficient of resonant frequency (τf ) generally decreased, although an obvious fluctuation was observed for x =3/4. 相似文献
3.
Rick Ubic Ian M. Reaney William E. Lee 《Journal of the American Ceramic Society》1999,82(5):1336-1338
The space group of the solid solution phase Ba6-3 x -RE8+2 x Ti18 O54 (RE = rare-earth cation) has been variously reported as Pba 2 (No. 32), Pbn 21 (No. 33), Pbam (No. 55), or Pbnm (No. 62). New results are presented here which indicate that its correct space group assignment may be Pb 21 m (No. 26). 相似文献
4.
Karen M. Cruickshank Xiping Jing Graeme Wood Eric E. Lachowski Anthony R. West 《Journal of the American Ceramic Society》1996,79(6):1605-1610
A solid-solution phase with the general formula Ba6-3x Nd8+2x Ti18 O54 , where 0.25(5) ≤×≤ 0.75(5), has been characterized at 1250°C; this phase has been variously described as BaNd2 Ti4 O12 and BaNd2 Ti5 O14 in the literature. Variation in its stoichiometry is accommodated via the cation substitution mechanism, 3Ba2 ⇆2Nd3+ . The location and extent of the solid solution were demonstrated by a combination of phase diagram studies and X-ray diffraction techniques, including lattice parameter measurements and electron microscopy. A combination of techniques was employed due to the insensitivity of secondary phase detection by X-ray diffraction in this system. Using this approach, a second possible solid-solution mechanism, Ba2+ 2Nd3+ ⇆2Ti4+ , is discounted. 相似文献
5.
Tin (Sn) substitution into the B-site and Nd/Sn cosubstitution into the A- and B-sites were investigated in a Ba 6−3 x Sm8+2 x Ti18 O54 solid solution ( x = 2/3). A small amount of tin substitution for titanium improved the temperature coefficient of resonant frequency (τf ) but led to a decrease of the relative dielectric constant (ɛ) and the quality factor ( Qf ). The Ba6−3 x Sm8+2 x (Ti1− z Snz )18 O54 -based tungsten-bronze phase became unstable for compositions with a tin content of ≥10 mol%, where BaSm2 O4 and Sm2 (Sn,Ti)2 O7 appeared, and finally, these phases became the major phases. On the other hand, Nd/Sn cosubstitution led to a good combination of high ɛ, high Qf , and near-zero τf . Excellent microwave dielectric properties were achieved in Ba6−3 x (Sm1− y Nd y )8+2 x (Ti1− z Sn z )18 O54 ceramics with y = 0.8 and z = 0.05 sintered at 1360°C for 3 h: ɛ= 82, Qf = 10 000 GHz, and calculated τf =+17 ppm/°C. The tolerance factor and electronegativity difference exhibited important effects on the microwave dielectric properties, especially the Qf value. A large tolerance factor and high electronegativity difference generally led to a higher Qf value. 相似文献
6.
Om Parkash Hari Shanker Tewari Lakshman Pandey Ravindra Kumar Devendra Kumar 《Journal of the American Ceramic Society》1989,72(8):1520-1522
Attempts have been made to synthesize the compositions with x = 0.01, 0.05, 0.10, 0.20, 0.30, 0.40, and 0.50 in the valence-compensated solid-solution Ba1–x Lax Ti1–x Nix O3 by ceramic methods. Solid solutions formed in the compositions with x0.10. The structure of the composition with x = 0.01 is tetragonal, whereas samples with x = 0.05 and 0.10 are cubic. A ferroelectric-paraelectric transition is observed only in the composition with x = 0.01 at ∼ 350 K. 相似文献
7.
8.
Joseph R. Spann Isabel K. Lloyd † Manfred Kahn Mark T. Chase ‡ 《Journal of the American Ceramic Society》1990,73(2):435-438
A single calcination step, solid-state process that provides orthohombic Ba2 YCu3 O7 powder is described. BaCO3 , Y2 O3 , and CuO are used as precursor materials. The only phase identifiable by X-ray diffraction is the orthorhombic Ba2 YCu3 O7 . The use of a vacuum during the inital stages of the calcining process promotes complete decomposition of the carbonate, and no residual carbonate is observed. An oxygen atmosphere during the later stages of calcining ensures proper oxidation to Ba2 YCu3 O7 . The use of a similar combination vacuum-oxygen calcining schedule should also be beneficial in the preparation of chemically derived powders. 相似文献
9.
BaTi4 O9 and Ba2 Ti9 O20 precursors were prepared via a sol–gel method, using ethylenediaminetetraacetic acid as a chelating agent. The sol–gel precursors were heated at 700°–1200°C in air, and X-ray diffractometry (XRD) was used to determine the phase transformations as a function of temperature. Single-phase BaTi4 O9 could not be obtained, even after heating the precursors at 1200°C for 2 h, whereas single-phase Ba2 Ti9 O20 (as determined via XRD) was obtained at 1200°C for 2 h. Details of the synthesis and characterization of the resultant products have been given. 相似文献
10.
Thermal expansion behaviors of Ba6−3 x Ln8+2 x Ti18 O54 (Ln=La, Nd, and Sm, x =0.5, 0.67, and 0.75) ceramics were determined by dilatometric measurement. The samples of all investigated compositions expanded nearly linearly with increasing temperature in the range of 20°–1200°C. Their thermal expansion coefficients were determined to be 10.7–11.4 ppm/°C. A discontinuous change in sample size was observed at about 1350°C for each composition, indicating the existence of a phase transition. As determined by the high-resolution X-ray diffraction analysis, the phase constitution and the lattice parameters of Ba6−3 x Sm8+2 x Ti18 O54 ceramics were maintained in the quenched samples. The origin of the phase transition was discussed thoroughly. Phase equilibrium in the BaTiO3 –Ln2/3 TiO3 system was reviewed by considering the phase transition. 相似文献
11.
Hiroshi Irie Masaru Miyayama Tetsuichi Kudo 《Journal of the American Ceramic Society》2000,83(11):2699-2704
Ba2 Bi4 Ti5 O18 single crystals were grown, and their dielectric permittivity, conductivity, and ferroelectricity were investigated along the a -(or b -)axis and the c -axis separately. The dielectric permittivity at 1 MHz along the a -(or b -)axis was 2000 at the Curie temperature (360°C); this value was 8 times greater than that along the c -axis. The dc conductivity was greater along the a -(or b -)axis than that along the c -axis, by one order of magnitude. In regard to the ferroelectricity, the saturated remanent polarization was 120 mC/m2 and the saturated coercive field was 3 MV/m along the a -(or b -)axis; values of 8.5 mC/m2 and 0.81 MV/m, respectively, were observed along the c -axis. The Ba2 Bi4 Ti5 O18 single crystals had large electrical anisotropies, which were due to the layered structure. 相似文献
12.
The electrical properties of Sr0.5 Ba0.3 TiO3 in the presence of Nb2 O5 as a donor, 3Li2 O · 2SiO2 as a sintering agent, and Bi2 O3 as a dopant have been studied. When the compositions of the ceramics were 1 mol Sr0.7 Ba0.3 TiO3 + 0.5 mol% Nb2 O5 + 2 mol% 3Li2 O · 2SiO2 + 0.2 mol% Bi2 O3 , the ceramics were sintered at 1100°C and exhibited the following characteristics: apparent dielectric constant ɛ, 25000; loss factor tan δ, 2%; insulating resistivity ρj , 1010 Ω· cm; variation of dielectric constant with temperature Δɛ/ɛ (−25° to +85°C), +10%, −14%. ɛ and tan δ show only small changes with frequency. The study shows this ceramic can be used in multilayer technology. 相似文献
13.
Hsin-chun Lu Lawrence E. Burkhart Glenn L. Schrader 《Journal of the American Ceramic Society》1991,74(5):968-972
Barium titanate precursors with Ba/Ti ratio 2:9 and 1:5 were prepared by first hydrolyzing titanium alkoxide and then mixing the resulting titania sol with a barium alkoxide-methanol solution. After drying, the xerogels of the precursors of barium titanates were sintered at temperatures from 700°C (4 h) to 1200°C (110 h or longer). Characterization of the product was performed using X-ray diffraction and laser Raman spectroscopy. At 700°C, BaTi5 O11 was formed from the 1:5 precursor and a two-phase mixture of BaTi2 O5 and BaTi5 O11 was formed from the 2:9 precursor. After prolonged heating at 1200°C, the latter mixture converted to a single-phase material, Ba2 Ti9 O20 . 相似文献
14.
Hui Zhang Liang Fang Heping Su Qian Yu Bolin Wu 《Journal of the American Ceramic Society》2009,92(1):238-240
Single-phase polycrystalline microwave dielectric ceramics Ba6 Ti1− x Sn x Nb4 O18 , with x changing from 0 to 1, were synthesized by the solid-state reaction method. All the solid solutions fitted well with A6 B5 O18 cation-deficient hexagonal perovskite structure. The substitution of Sn for Ti effectively enhanced the quality factor and controlled τf . With increasing Sn content, the dielectric constant decreased from ∼47 to ∼32, and the Q × f value increased significantly from 11 530 to 28 496 GHz, with τf varying from 64 to 0 ppm/°C. A zero τf was realized when Sn was fully replaced by Ti with the composition Ba6 SnNb4 O18 . 相似文献
15.
Ba6−3 x Sm8+2 x Ti18 O54 ( x =2/3) (BST) was prepared by the solid-state method and the effect of bismuth borate (BB)/LiF on the sinterability, microstructure, and thermal and microwave dielectric properties were studied. BST+3.5 wt% BB+0.5 wt% LiF composite sintered at 1050°C has Q × f =4500 GHz, ɛ=52, and τ f =+6 ppm/°C. Raman spectrum of the composite was compared with that of BST and the structural changes were investigated. 相似文献
16.
The superplastic behavior of YBa2 Cu3 O7− x ceramic superconductors was studied. Large compressive deformation over 100% strain was measured in the temperature range of 775°–875°C, with a strain rate of 1 × 10−5 to 1 × 10−3 /s, and a grain size of 0.5–1.4 μm. The nature of the deformation was investigated in terms of three deformation parameters: the stress exponent ( n ), the grain size exponent ( p ), and the activation energy ( Q ). The measured values of these parameters were n = 2 ± 0.3, p = 2.7 ± 0.7, and Q = 745 ± 100 kJ/mol. With the aid of the deformation map, the deformation mechanism was identified as grain boundary sliding accommodated by grain boundary diffusion. The conclusion is consistent with the microstructural observations made by SEM and TEM: the invariance of equiaxed grain shape, the absence of significant dislocation activity, no grain boundary second phases, and no significant texture development. 相似文献
17.
Hiroaki Takeda Masataka Ohgaki Takashi Kizuki Kazuaki Hashimoto Yoshitomo Toda Shigekazu Udagawa Kimihiro Yamashita 《Journal of the American Ceramic Society》2000,83(11):2884-2886
The formation process of Ba2 La8 (SiO4 )6 O2 was clarified using thermogravimetry–differential thermal analysis (TG-DTA) and a high-temperature powder X-ray diffraction (HT-XRD) method. Phase changes identified from the HT-XRD data surprisingly corresponded to the weight loss and/or endothermic peaks observed in the TG-DTA curves. Raw material with the composition Ba2 La8 (SiO4 )6 O2 was completely reacted at 1400°C and produced only an apatite-type compound without a secondary phase. Moreover, the synthesis of Ba2+ x La8− x (SiO4 )6 O2−δ crystals with x = 0–2 was attempted using a solid-state reaction. 相似文献
18.
La2 Ti2 O7 powders were prepared using three different techniques. Single-phase material was obtained at 1150°C by calcination of mixed oxides, at 1000°C by molten salt synthesis, and at 850°C by evaporative decomposition of solutions. Particle sizes and morphologies of the powders differed substantially, as did the sintered microstructures and dielectric properties. Very dense (99%), translucent, grain-oriented lanthanum titanate was fabricated by hot-forging at 1300°C under a 200-kg load. Anisotropy was demonstrated by X-ray diffraction, scanning electron microscopy, thermal expansion, and dielectric measurements. 相似文献
19.
This report details development of a route to solution-derived (1− x )Bi1/2 Na1/2 TiO3 · x BaTiO3 powders. The method developed was the citrate-gel method—an evaporative, aqueous technique. When applied to 0.95Bi1/2 Na1/2 TiO3 ·0.05BaTiO3 (BNBT-5), the method produced perovskite phase powders that readily densified in the temperature range of 1000°C. The grain size of the sintered materials was on the order of 1 μm, and the weak-field dielectric properties at 1 MHz were similar to those reported for conventionally prepared materials sintered at higher temperatures (e.g., 1200°C). 相似文献
20.
Yang-Il Jung Byoung-Ki Lee Suk-Joong L. Kang 《Journal of the American Ceramic Society》2004,87(4):739-741
A structural transition of Ba6 Ti17 O40 /BaTiO3 interfaces from faceted to rough was induced by reducing oxygen partial pressure in the atmosphere. As the oxygen partial pressure decreased, the number densities of {111} twins and abnormal grain decreased. TEM observation showed that the twin formation was governed only by the faceting of the interface. Experimental evidence of {111} twin-assisted abnormal growth of faceted BaTiO3 grains was also obtained. 相似文献