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1.
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
2.
Dong-Wan Kim Jeong-Ryeol Kim Sung-Hun Yoon Kug Sun Hong Chang Kyung Kim 《Journal of the American Ceramic Society》2002,85(11):2759-2762
The effect of B2 O3 on the sintering temperature and microwave dielectric properties of Ba5 Nb4 O15 has been investigated using X-ray powder diffraction, scanning electron microscopy, and a network analyzer. Interactions between Ba5 Nb4 O15 and B2 O3 led to formation of second phases, BaNb2 O6 and BaB2 O4 . The addition of B2 O3 to Ba5 Nb4 O15 resulted in lowering the sintering temperature from 1400° to 925°C. Low-fired Ba5 Nb4 O15 could be interpreted by measuring changes in the quality factor ( Q × f ), the relative dielectric constant (ɛr ), and the temperature coefficient of resonant frequency (τf ) as a function of B2 O3 additions. More importantly, the formation of BaNb2 O6 provided temperature compensation. The microwave dielectric properties of low-fired Ba5 Nb4 O15 had good dielectric properties: Q × f = 18700 GHz, ɛr = 39, and τf = 0 ppm/°C. 相似文献
3.
EKKEHART TILLMANNS WOLFGANG HOFMEISTER WERNER H. BAUR 《Journal of the American Ceramic Society》1983,66(4):268-271
A single-crystal X-ray study of dibarium nonatitanate, Ba2 Ti9 O20 , yielded the triclinic space group P 1 with a =0.7471(1), b= 1.4081(2), c= 1.4344(2) nm, α=89.94(2)°, β= 79.43(2)°, γ= 84.45(2)°, V = 1.476 nm3 Z = 4, and Dx = 4.61 Mg/m3 . A refinement of atomic coordinates and isotropic thermal parameters led to a residual of 0.03. The structure consists of hexagonally closest-packed layers of Ba and O atoms in the sequence (hch)3 . All Ti atoms reside in octahedral interstices of this closest packing. The various Ti coordination octahedra share only edges and corners with each other. One-half of the Ba atoms is twelve-coordinated by oxygen atoms, the other half is eleven-coordinated. 相似文献
4.
The hexagonal perovskite, Ba8 ZnTa6 O24 , was prepared in single-phase form and was found to be a stable secondary phase, formed as a result of the loss of ZnO from Ba(Zn1/3 Ta2/3 )O3 microwave dielectrics. The experimental and calculated X-ray patterns of Ba8 ZnTa6 O24 indicate it is isostructural with Ba8 Ta6 NiO24 with an 8H (cchc)2 close-packed BaO3 stacking sequence and the lattice parameters, a =10.0825(14), c =19.0587(38)Å. High-density ceramics of Ba8 ZnTa6 O24 could be prepared at temperatures considerably lower (1400°C) than those used to sinter pure Ba(Zn1/3 Ta2/3 )O3 , and exhibit very good microwave dielectric properties with ɛ=30.5, Q f =62 300, and τf =+36 ppm/°C at 8.9 GHz. 相似文献
5.
Girish Harshé Dinesh Agrawal Santosh Limaye 《Journal of the American Ceramic Society》1994,77(7):1965-1968
The NaZr2 P3 O12 (NZP) family of materials is attracting increasing attention due to its low-thermal-expansion behavior. The system Ba1+x Zr4 P6–2x Si2x O24 (0 ≤ x ≤ 1), belonging to the NZP family, shows ultralow thermal expansion over a wide temperature range. It also shows anisotropy in its lattice thermal expansion. This causes microcracking as the sintered specimens are cooled, which results in degradation of the mechanical properties. In this work, the chemical stability, strength, and Young's modulus of Ba1+x Zr4 P6–2x O24 ( X = 0.25 and 0.5) ceramics at high temperatures have been determined. An attempt has been made to correlate the mechanical properties to the thermal expansion anisotropy. 相似文献
6.
Jana Bezjak Aleksander Renik Botjan Janar Philippe Boullay Ivana Radosavljevi Evans Danilo Suvorov 《Journal of the American Ceramic Society》2009,92(8):1806-1812
Polymorphic phase transitions in Ba4 Nb2 O9 were studied by thermal analyses, high-temperature transmission electron microscopy and X-ray powder diffractometry. Two stable polymorphs were isolated, low-temperature α-modification and high-temperature γ-modification, with the endothermic phase transition at 1176°C. The α→γ transformation is accompanied by the formation of a 120° domain structure, which is a consequence of hexagonal→orthorhombic unit cell reconstruction. Reheating the presintered γ-Ba4 Nb2 O9 results in the formation of a metastable γ'-modification (formerly known as β-polymorph) in the temperature range between 360° and 585°C, before the γ→α transformation at 800°C. Above ∼490°C Ba4 Nb2 O9 becomes moderately sensitive to a loss of BaO. In air the surface of Ba4 Nb2 O9 grains decomposes to nanocrystalline Ba5 Nb4 O15 and BaO, which instantly reacts with atmospheric CO2 to form BaCO3 . Surface reaction delays γ→α transformation up to 866°C in air. In vacuum the loss of BaO is even more enhanced and consequently the formation of minor Ba3 Nb2 O8 phase is observed above 1150°C. 相似文献
7.
A TEM investigation was conducted on the structure of a second phase precipitated between the grains of a polycrystalline TiO2 -rich BaTiO3 which was doped with 8 mol% Ca. This phase was identified as Ca-stabilized Ba2 Ti5 O12 with a 10-layer orthorhombic structure and unit-cell parameters a=0.990, b=1.131, and c=2.330 nm. 相似文献
8.
Mi-Ri Joung Jin-Seong Kim Myung-Eun Song Sahn Nahm Jong-Hoo Paik Byung-Hyun Choi 《Journal of the American Ceramic Society》2009,92(7):1621-1624
The formation process and microwave dielectric properties of the Mg2 V2 O7 ceramics were investigated. The MgV2 O6 phase that was formed at around 450°C interacted with remnant MgO above 590°C to form a homogeneous monoclinic Mg2 V2 O7 phase. Finally, this monoclinic Mg2 V2 O7 phase was changed to a triclinic Mg2 V2 O7 phase for the specimen fired at 800°C. Sintering at 950°C for more than 5 h produced high-density triclinic Mg2 V2 O7 ceramics. In particular, the Mg2 V2 O7 ceramics sintered at 950°C for 10 h exhibited the good microwave dielectric properties of ɛr =10.5, Q × f =58 275 GHz, and τf =−26.9 ppm/°C. 相似文献
9.
Stephan Senz reas Graff Werner Blum Dietrich Hesse Hans-Peter Abicht 《Journal of the American Ceramic Society》1998,81(5):1317-1321
Fresnoite grows at 700° and 800°C, and Ba6 Ti7 O40 grows at 1200°C with definite orientations, which are determined by X-ray diffraction pole figure analysis. Partially textured fresnoite is formed at higher temperatures. The SiO2 films react with the BaTiO3 crystals, forming the phases Ba2 TiSi2 O8 (fresnoite) and Ba6 Ti17 O40 . At 700° and 800°C, both phases grow with definite orientations, which are determined by X-ray diffraction pole figure analysis. Partially textured polycrystalline phases are formed at higher temperatures. 相似文献
10.
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
11.
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
12.
A narrow region of Zn-vacancy-containing cubic perovskites was formed in the (1− x )Ba3 (ZnNb2 )O9 −( x )Ba3 W2 O9 system up to 2 mol% substitution ( x =0.02). The introduction of cation vacancies enhanced the stability of the 1:2 B-site ordered form of the structure, Ba(Zn1− x □ x )1/3 (Nb1− x W x )2/3 O3 , which underwent an order–disorder transition at 1410°C, ∼35° higher than pure Ba(Zn1/3 Nb2/3 )O3 . The Zn vacancies also accelerated the kinetics of the ordering reaction, and samples with x =0.006 comprised large ordered domains with a high lattice distortion ( c/a =1.226) after a 12 h anneal at 1300°C. The tungstate-containing solid solutions can be sintered to a high density at 1390°C, and the resultant ordered ceramics exhibit some of the highest microwave dielectric Q factors ( Q × f =1 18 000 at 8 GHz) reported for a niobate-based perovskite. 相似文献
13.
Naoto Hirosaki Yoshinobu Yamamoto Toshiyuki Nishimura Mamoru Mitomo Junichi Takahashi Hisanori Yamane Masahiko Shimada 《Journal of the American Ceramic Society》2002,85(11):2861-2863
Phase relationships in the Si3 N4 –SiO2 –Lu2 O3 system were investigated at 1850°C in 1 MPa N2 . Only J-phase, Lu4 Si2 O7 N2 (monoclinic, space group P 21 / c , a = 0.74235(8) nm, b = 1.02649(10) nm, c = 1.06595(12) nm, and β= 109.793(6)°) exists as a lutetium silicon oxynitride phase in the Si3 N4 –SiO2 –Lu2 O3 system. The Si3 N4 /Lu2 O3 ratio is 1, corresponding to the M-phase composition, resulted in a mixture of Lu–J-phase, β-Si3 N4 , and a new phase of Lu3 Si5 ON9 , having orthorhombic symmetry, space group Pbcm (No. 57), with a = 0.49361(5) nm, b = 1.60622(16) nm, and c = 1.05143(11) nm. The new phase is best represented in the new Si3 N4 –LuN–Lu2 O3 system. The phase diagram suggests that Lu4 Si2 O7 N2 is an excellent grain-boundary phase of silicon nitride ceramics for high-temperature applications. 相似文献
14.
Ba6−3 x Nd8+2 x Ti18 O54 ceramic powders were synthesized by the modified Pechini method using ethylenediaminetetraacetic acid (EDTA) as a chelating agent. A purplish red, molecular-level, homogeneously mixed gel was prepared, and transferred into a porous resin intermediate through charring. Single-phase and well-crystallized Ba6−3 x Nd8+2 x Ti18 O54 powders were obtained from pulverized resin at a temperature of 900°C for 3 h, without formation of any intermediate phases. Meanwhile, the molar ratio of EDTA to total metal cation concentration had a significant influence on the crystallization behavior of Ba6−3 x Nd8+2 x Ti18 O54 . The Ba6−3 x Nd8+2 x Ti18 O54 ( x = 2/3) ceramics prepared via EDTA precursor have excellent microwave dielectric characteristics: ɛ= 87, Qf = 8710 GHz. 相似文献
15.
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
16.
TiO2 above 4 mol% is an effective nucleating agent for CaO–P2 O5 glass which also contains substantial SiO2 and Al2 O3 additions. Glass ceramics can be made from this glass using a single slow heating ramp with no need for a nucleating heat treatment step. Powder of this composition crystallizes rapidly to β-Ca2 P2 O7 , whereas bulk glass crystallizes from diphasic nuclei consisting of a central cubic Ca-P-Ti-Si-Al oxide phase surrounded by impure AlPO4 dendrites. Metastable calcium phosphate grows on the AlPO4 dendrites and later transforms to β-Ca2 P2 O7 . 相似文献
17.
Mi-Ri Joung Jin-Seong Kim Myung-Eun Song Jae-Hong Choi Jong-Woo Sun Sahn Nahm Jong-Hoo Paik Byung-Hyun Choi 《Journal of the American Ceramic Society》2009,92(9):2151-2154
Li2 CO3 was added to Mg2 V2 O7 ceramics in order to reduce the sintering temperature to below 900°C. At temperatures below 900°C, a liquid phase was formed during sintering, which assisted the densification of the specimens. The addition of Li2 CO3 changed the crystal structure of Mg2 V2 O7 ceramics from triclinic to monoclinic. The 6.0 mol% Li2 CO3 -added Mg2 V2 O7 ceramic was well sintered at 800°C with a high density and good microwave dielectric properties of ɛ r =8.2, Q × f =70 621 GHz, and τf =−35.2 ppm/°C. Silver did not react with the 6.0 mol% Li2 CO3 -added Mg2 V2 O7 ceramic at 800°C. Therefore, this ceramic is a good candidate material in low-temperature co-fired ceramic multilayer devices. 相似文献
18.
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
19.
J. K. PLOURDE D. F. LINN H. M. O'BRYAN Jr .JOHN THOMSON Jr . 《Journal of the American Ceramic Society》1975,58(9-10):418-420
Microwave measurements of Ba2 Ti9 O20 show that this ceramic is uniquely suited for dielectric resonators. (Suitable ceramics should have a high dielectric constant K , a low dielectric loss (high Q ), and a low temperature coefficient of resonant frequency, τ.) At 4 GHz, Ba2 Ti9 O20 resonators have Q >8000, K = 39.8, and τ=2 ppm/°C. Measurements of Q and τ were made on unmetallized ceramic resonator disks positioned in a waveguide; K was measured using a dielectric post resonator technique. From 4 to 10 GHz, Q approaches that for a copper waveguide cavity, whereas the temperature coefficient is typically 8 times lower. 相似文献
20.
The effect of the addition of V2 O5 on the structure, sintering and dielectric properties of M -phase (Li1+ x − y Nb1− x −3 y Ti x +4 y )O3 ceramics has been investigated. Homogeneous substitution of V5+ for Nb5+ was obtained in LiNb0.6(1− x ) V0.6 x Ti0.5 O3 for x ≤ 0.02. The addition of V2 O5 led to a large reduction in the sintering temperature and samples with x = 0.02 could be fully densified at 900°C. The substitution of vanadia had a relatively minor adverse effect on the microwave dielectric properties of the M -phase system and the x = 0.02 ceramics had [alt epsilon]r = 66, Q × f = 3800 at 5.6 GHz, and τf = 11 ppm/°C. Preliminary investigations suggest that silver metallization does not diffuse into the V2 O5 -doped M -phase ceramics at 900°C, making these materials potential candidates for low-temperature cofired ceramic (LTCC) applications. 相似文献