共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
X. M. Chen Y. Suzuki N. Sato 《Journal of Materials Science: Materials in Electronics》1994,5(4):244-247
The sinterability of Ba(Mg1/3Ta2/3)O3 ceramics synthesized by solid-state-reaction methods was investigated. The poor sinterability of the present ceramics was found to be primarily due to the presence of satellite secondary phases of Ba5Ta4O15 and Ba4Ta2O9, and the nearly complete densification of Ba(Mg1/3Ta2/3)O3 ceramics was accomplished successfully by controlling the phase constitution of the calcined powders. For this purpose, enhanced ball-milling processes were found to be extremely effective. Moreover, excellent microwave dielectric characteristics (r = 24.5–24.7, Q = 26 000 at 9.8 GHz, and f = 1.7 p.p.m. C–1) were attained in the dense Ba(Mg1/3Ta2/3)O3 ceramics without additives. 相似文献
3.
X. M. Chen 《Journal of Materials Science》1996,31(18):4853-4857
Dielectric characteristics of composite ceramics in the system Ba(Mg1/3Ta2/3)O3-BaO · Nd2O3 · 5TiO2 were investigated to search for a new candidate system for microwave dielectric ceramics with modifiable dielectric constant, low dielectric loss and small temperature dependence. The dielectric constant could be adjusted in the range 25–81 by controlling the concentration of BaO · Nd2O3 · 5TiO2, while the dielectric loss remained of the order of 10–4 for some compositions. Moreover, the dielectric properties in the present system could be significantly improved by post-densification thermal treatment. 相似文献
4.
Structural order in Ba(Zn1/3Ta2/3)O3, Ba(Zn1/3Nb2/3)O3 and Ba(Mg1/3Ta2/3)O3 microwave dielectric ceramics 总被引:4,自引:0,他引:4
The process and nature of structural ordering and the factors that influence them have been investigated in the microwave
dielectric perovskites, barium zinc tantalate (BZT), barium zinc niobate (BZN), and barium magnesium tantalate (BMT), sintered
at various temperatures. The samples were characterized mainly by X-ray powder diffraction and transmission electron microscopy.
The results show that short-range 1 : 1 B-site order features strongly in the early stages of ordering in BZT and BZN, but
it is extremely rare in BMT, for which most grains commence with 1 : 2 order. As sintering progresses, 1 : 1 order is replaced
by 1 : 2 long-range order in BZT and by disorder in BZN. Orientational variants of the ordered domains within grains occur
in similar numbers when order is fine-scale, but their distribution is less homogeneous in well-ordered samples. Local inhomogeneities
in the degree of order within grains, which will affect dielectric properties, correlate with both residual non-stoichiometry
and the presence of dislocations. Incompletely reacted starting materials which may persist to late stages of sintering can
also strongly influence order. Anomalously large ordered domains at grain boundaries are attributed to grain-boundary migration
accompanied by enhanced diffusion. The results indicate that with starting materials that are well-mixed and homogeneous at
the nanoscale, tailoring of physical properties should be possible by controlling the type and degree of order through chemical
composition.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
5.
The effects of NaF additive upon the sintering temperature of Ba(Mg1/3Ta2/3)O3 dielectric ceramics were investigated, and the densification of the present ceramics could be performed well at lower temperatures, even around 1200 C, when the concentration of NaF additive was equal or greater than 2 wt %. Moreover, no secondary phase was observed in such ceramics, except the limited surface layers. 相似文献
6.
7.
Amodini Mishra S. N. Choudhary R. N. P. Choudhary V. R. K. Murthy Kamal Prasad 《Journal of Materials Science: Materials in Electronics》2012,23(1):185-192
A new lead-free perovskite Ba(Bi1/2Ta1/2)O3 was prepared by conventional ceramic fabrication technique at 1,200 °C/4 h in air atmosphere. The crystal symmetry, space group and unit cell dimensions were determined from the experimental results using FullProf software. The crystallite size and lattice strain were estimated from Williamson-Hall approach. XRD analysis of the compound indicated the formation of a single-phase cubic structure with the space group Pm3m. EDAX and SEM studies were carried out in order to evaluate the quality and purity of the compound. Permittivity data showed a low temperature coefficient of capacitance (T CC < 4%) up to +125 °C. Complex impedance analyses suggested the dielectric relaxation to be of non-Debye type. Electric modulus studies supported the hopping type of conduction in Ba(Bi1/2Ta1/2)O3. 相似文献
8.
A new phase of Ba(Mg1/3Ta2/3)O3 has been obtained by calcination at 1400°C. It belongs to the cubicPm3m witha = 4·08840(4)Å and the crystal structure has been found to be the ideal perovskite by the Rietveld method from powder X-ray diffraction data. 相似文献
9.
《Materials Research Bulletin》2006,41(4):784-790
The microwave dielectric properties of ceramics based on Ba(Mg1/3Ta(2−2x)/3Wx/3Tix/3)O3 is investigated as a function of x. The densification as well as dielectric properties deteriorate with increase in the substitution levels of (Ti1/3W1/3)3.33+ at (Ta2/3)3.33+ site in Ba(Mg1/3Ta2/3)O3. The τf is approaching zero between x = 0.1 and 0.15 in Ba(Mg1/3Ta(2−2x)/3Wx/3Tix/3)O3 where quality factor is reasonably good (Qu × f = 80,000–90,000 GHz). The Ba(Mg1/3Ta(2−2x)/3Wx/3Tix/3)O3 with x = 1.0 has ɛr = 15.4, τf = −25.1 ppm/°C, Qu × f = 35,400 GHz. 相似文献
10.
《Materials Research Bulletin》2004,39(4-5):629-636
The microstructures and the microwave dielectric properties of barium magnesium tantalate ceramics prepared by conventional mixed oxide route have been investigated. The prepared Ba(Mg1/3Ta2/3)O3 exhibited a mixture of cubic perovskite and a hexagonal superstructure with Mg and Ta showing 1:2 order in the B-site. It is found that low level doping of V2O5 (up to 0.5 wt.%) can significantly improve densification of the specimens and their microwave dielectric properties. The density of doped Ba(Mg1/3Ta2/3)O3 ceramics can be increased beyond 95% of its theoretical value by 1500 °C-sintering, which is caused by the liquid-phase effect of V2O5 addition. The detected second phase Ta2O5 was mainly the result of V5+ substitution in the ceramics. Dielectric constant (εr) and temperature coefficient of resonant frequency (τf) were not significantly affected, while the unloaded quality factors Q were effectively promoted by V2O5 addition due to the increase in B-site ordering. The εr value of 24.1, Q×f value of 149,000 (at 10 GHz) and τf value of 7.2 ppm/°C were obtained for Ba(Mg1/3Ta2/3)O3 ceramics with 0.25 wt.% V2O5 addition sintered at 1500 °C for 3 h. 相似文献
11.
Peng Sen Zhang Yu Tang Jiejia Zeng Wenfei Zhao Chenglin 《Journal of Materials Science: Materials in Electronics》2021,32(18):23309-23316
Journal of Materials Science: Materials in Electronics - This paper reported a research of the sinterability, microstructures, and microwave dielectric properties of Ba(Mg1/3Ta2/3)O3 (BMT) ceramics... 相似文献
12.
《Materials Research Bulletin》2006,41(7):1357-1363
The crystalline phase and the microwave dielectric properties of the Mg(Ta1−xNbx)2O6 ceramics have been investigated. Combining the positive temperature coefficient of the resonant frequency (τf) material (MgTa2O6, τf = +30 ppm/°C) with the negative one (MgNb2O6, τf = −70 ppm/°C) can produce the composite with τf ∼ 0 ppm/°C. The crystal structure of pure MgTa2O6 ceramic is the tetragonal structure. For x = 0.15, the crystal structure of the solid solution was the coexistence of the tetragonal structure and orthorhombic structure. Solid solutions with 0.25 ≦ x ≦ 1 exhibit the orthorhombic structure, which is like the structure of pure MgNb2O6 ceramic. The sintered morphologies of Mg(Ta1−xNbx)2O6 ceramics gradually change from the disk-typed grains (x = 0 and 0.15) to the disk-typed and bar-typed grains coexist (x = 0.35, 0.5, and 0.7), and then reveal the bar-typed grains (x = 0.85 and 1). The densities, dielectric constants (ɛr) and τf values of Mg(Ta1−xNbx)2O6 ceramics decrease with the increase of the MgNb2O6 content. The quality factor (Q × f) reaches the minimum value at x = 0.15, and then increases with the increase of the MgNb2O6 content. The Mg(Ta1−xNbx)2O6 ceramic with x = 0.25 sintered at 1450 °C exhibits a minimum τf value of −0.7 ppm/°C. 相似文献
13.
SEONG- JIN CHOI SAHN NAHM JAE-DONG BYUN KYUNG-SOO SUH HWACK JOO LEE HYUN RYU 《Journal of Materials Science Letters》1997,16(10):785-787
Abstracts are not published in this journal
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
14.
Powders of the microwave dielectric material barium magnesium tantalate Ba(Mg1/3Ta2/3)O3 have been produced by hydrothermal synthesis at moderately low temperatures (160 to 350°C). It was found that while it is relatively straightforward to produce the material in the desired perovskite phase at or below 200°C, the powder particles tend to be highly irregular in morphology with extremely small dimensions (of the order of 10 nm) and deficient in magnesium (with some precipitation of the excess magnesium as the hydroxide). The effects of both higher synthesis temperatures and different feedstock preparation were thus investigated with the aim of improving the precipitation of magnesium under hydrothermal conditions in order to produce a more homogeneous, stoichiometric powder and significant progress was made. It was found that when near-stoichiometric particles are formed, they adopt rounded morphologies and exhibit larger particle sizes (around 30–50 nm). These results show that the hydrothermal feedstock and the synthesis temperature used have a profound effect on particle stoichiometry, which in turn affects the growth morphology of the particles. 相似文献
15.
16.
Manoj Raama Varma N. D. Kataria 《Journal of Materials Science: Materials in Electronics》2007,18(4):441-446
Ba(Zn1/3Ta2/3)O3 has been prepared with different dopants that gave best microwave dielectric properties at room temperature. Effects of different
dopants on the low temperature microwave dielectric properties of BZT were investigated. With decrease in temperature, loss
tangent was found to decrease marginally and then increase at temperatures lower than 100 K. Increase in loss factor at lower
temperatures were found to be less for dopants with smaller ionic radii. Dielectric constant was found to be almost independent
of temperature. Temperature coefficient of resonant frequency slowly decreased from a positive value to negative value when
temperature was lowered. Temperature at which τf becomes zero was found to vary for different dopants. There is a temperature stable region for tanδ, ɛr and τf which varies for different dopants. 相似文献
17.
The dielectric and physical properties of the complex perovskite Ba(Mg1/3Ta2/3)O3 system in which magnesium was substituted for nickel from 0.03–0.67 mol%, were investigated in the temperature range 20–110C, and the frequency range 10.5–14.5 GHz. As the nickel content was increased, the dielectric constant, the degree of ordering, and the unloaded Q decreased. The temperature dependence of the dielectric constant and the temperature coefficient of resonant frequency of the specimens annealed at 1500C for 20 h were found to be greater than those of the specimens sintered at 1650C for 2 h. These results are due to the increase in the density, the increase in grain size, and the lattice distortion. 相似文献
18.
一种新型湿化学方法合成Ba(Mg1/3Ta2/3)O3纳米粉末的研究 总被引:1,自引:0,他引:1
介绍了一种工艺简便且成本较低的Ba(Mg1/3Ta2/3)O3(BMT)纳米粉末的湿化学制备方法.实验过程以Ta2O5作为起始物,通过热碱反应与钽离子浓度控制法合成Ta2O5@nH2O胶体,然后与Ba、Mg醋酸盐按化学计量比混合,经热处理制得BMT纳米粉末.实验结果表明该方法制备BMT粉体所需的合成温度仅为800℃,比传统固相反应法合成温度降低400℃左右,平均粒径仅为70nm.此外所制得的纳米陶瓷材料具有较佳的低温烧结性能和微波介电特性,比目前报道的醇盐系湿化学制备技术更具有实用性. 相似文献
19.
K. M. Manu S. Soni V. R. K. Murthy M. T. Sebastian 《Journal of Materials Science: Materials in Electronics》2013,24(6):2098-2105
The effect of Ba(Zn1/3Ta2/3)O3 (BZT) ceramic filler on the dielectric, mechanical and thermal properties of high density polyethylene (HDPE) matrix have been investigated. The dispersion of BZT particles in the matrix was varied up to 0.45 volume fraction (Vf). The SEM images confirmed the increase in connectivity between the filler particles with the increase in filler loading. All the composites showed excellent densification (>99 %) with relatively low moisture absorption (<0.04 wt%). The dielectric properties of the composites were investigated at 1 MHz, 5 GHz and at 10 GHz. The relative permittivity and the dielectric loss were found to increase as a function of BZT loading. Different theoretical models were used to predict the relative permittivity at 10 GHz. Effective medium theory gave the best correlation with the experimental results. An enhancement in the thermal conductivity (TC) and a reduction in the coefficient of linear thermal expansion (CTE) were achieved with filler loading. A slight decrease in the tensile strength was also observed with BZT loading. At 10 GHz, 0.45 Vf BZT reinforced HDPE showed a low relative permittivity (εr = 8.2) and a low dielectric loss (tanδ = 1.6 × 10?3) with good thermal (TC = 1.4 W m?1 K?1, CTE = 92 ppm/°C) and mechanical (tensile strength = 18 MPa) properties. 相似文献