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1.
Ba6 – 3x
(Sm1 – y
La
y
)8 + 2x
Ti18O54 solid solutions were prepared and characterized. For x = 2/3, tungsten bronze type solid solutions were observed in the entire range of y = 0–1. While, La substitution for Sm will change the phase constitution in Ba6 – 3x
Sm8 + 2x
Ti18O54 ceramics with x = 0.75. Though the single phase solid solutions were observed for the compositions at the vicinity of the end-members, La4Ti9O24 secondary phase was detected for the compositions of y = 0.3–0.8. For x = 2/3, the dielectric constant increased continuously with increasing y, and the Q · f value increased slightly at first then decreased. The dielectric constant had more complex change with increasing y for the situation of x = 0.75 where Q · f value decreased continuously. In both cases, the temperature coefficient of resonant frequency varied from negative to positive with increasing y. 相似文献
2.
Three novel Ba5LnNiTa9O30 (Ln = La, Nd and Sm) ceramics were prepared and characterized in the BaO-Ln2O3-NiO-Ta2O5 system. All three compounds adopted the filled tetragonal tungsten bronze (TB) structure at room temperature. The present
ceramics exhibited relaxor behavior, and the Curie temperature (at 10kHz) were −130, −80 and −45°C for Ba5LaNiTa9O30, Ba5NdNiTa9O30, and Ba5SmNiTa9O30 respectively. At room temperature, Ba5LnNiTa9O30 ceramics have a high dielectric constants in the range 102∼118, a low dielectric loss in range 0.0019∼0.0036, and the temperature
coefficients of the dielectric constant (τɛ) in the range −320∼−460 ppm°C−1 (at 1 MHz). 相似文献
3.
采用微波快速烧结法制备了La掺杂CaCu3Ti4O12致密陶瓷,研究了其结构、介电和压敏性能。所有Ca1-3x/2LaxCu3Ti4O12陶瓷均形成了CCTO晶相,但是La含量低于0.10时存在CuO第二相。随着La含量增加,Ca1-3x/2LaxCu3Ti4O12陶瓷介电常数随频率和温度变化越来越小;压敏电压逐渐增大,非线性系数也明显改善。其中La含量x=0.15时,Ca1-3x/2LaxCu3Ti4O12陶瓷具有良好的压敏性能:压敏电场强度为5.25 kV/cm,非线性系数为26.3。 相似文献
4.
MgTiO3/CaTiO3 layered ceramics with differently stacking were fabricated and the microwave dielectric properties were evaluated with TE011 mode. With increasing CaTiO3 thickness fraction, the resonant frequency decreased and the dielectric constant increased with a near-linear relation for
the bi-layer ceramics, while the values of the tri-layer MgTiO3/CaTiO3/MgTiO3 ceramics with thickness ratio of 1:1:1 derived much from the curves of the bi-layer ceramics. The finite element method was
used to give an explanation for the differences between the bi-layer and tri-layer ceramics. 相似文献
5.
6.
7.
在CaO-SrO-Li2O-Sm2O3-Nd2O3-TiO2(简称CSLLT)陶瓷中加入BaCu(B2O5)(简称BCB),研究了BCB对CSLLT陶瓷的烧结特性和介电性能的影响。结果表明:随BCB的添加,CSLLT陶瓷的烧结温度逐渐下降,并且具有高介电常数。其中,添加10?B后的CSLLT陶瓷其烧结温度从1 300℃显著下降到1 050℃,且在微波频率下具有如下介电性能:ε=77.3、Qf=4 735 GHz;τf=-48.1×10-6/℃(1 MHz)。 相似文献
8.
Microwave dielectric properties of low temperature sintering ZnNb2O6 ceramics doped with CuO-V2O5-Bi2O3 additions were investigated systematically. The co-doping of CuO, V2O5 and Bi2O3 can significantly lower the sintering temperature of ZnNb2O6 ceramics from 1150 to 870C. The secondary phase containing Cu, V, Bi and Zn was observed at grain boundary junctions, and the amount of secondary phase increased with increasing CuO-V2O5-Bi2O3 content. The dielectric properties at microwave frequencies (7–9 GHz) in this system exhibited a significant dependence on the relative density, content of additives and microstructure of the ceramics. The dielectric constant ( r) of ZnNb2O6 ceramics increased from 21.95 to 24.18 with increasing CuO-V2O5-Bi2O3 additions from 1.5 to 4.0 wt%. The quality factors (Q× f) of this system decreased with increasing CuO-V2O5-Bi2O3 content and ranged from 36118 to 67100 GHz for sintered ceramics, furthermore, all Q× f values of samples with CuO-V2O5-Bi2O3 additions are lower than that of un-doped ZnNb2O6 ceramics sintered at 1150C for 2 h. The temperature coefficient of resonant frequency ( f) changed from –33.16 to –25.96 ppm/C with increasing CuO-V2O5-Bi2O3 from 1.5 to 4.0 wt% 相似文献
9.
10.
Ceramics in the Na(Ta1 − xNbx)O3 system were prepared by a solid state reaction approach, and their dielectric characteristics were evaluated together with the structures. The complete solid solution with orthorhombic structures was observed in the present system, and three supposed phase transitions at about 475, 580 and 650∘C were observed by DTA. Only one dielectric anomaly was observed at high temperature for x = 0.2 and 0.4, and alternative dielectric anomaly (a diffused dielectric peak) was observed around 170 and 380∘C for x = 0.6 and 0.8, respectively. The compositions of 0.6 and 0.8 are weakly ferroelectric and those of 0.2 and 0.4 are supposed to be antiferroelectric at room temperature. 相似文献
11.
(Zr0.8,Sn0.2)TiO4 (ZST) ceramics were prepared by solid-state reaction method with 1 wt% ZnO and 0.5–1.5 wt% CeO2 or Nd2O3 as sintering aids. The effect of processing parameters and additive concentration on the structure, microstructure and microwave dielectric properties of ZST ceramics were investigated. The dielectric constant (?r) and temperature coefficient of the resonance frequency (τf) were not significantly affected by the addition of these additives. The unloaded quality factors (Qu) were effectively promoted by CeO2 and Nd2O3 additions. ?r values of 40 and 38.3, Qxfo values of 57,500 and 59,300 were obtained for the samples sintered with 1.5 and 0.5 wt% of CeO2 and Nd2O3 respectively. The improvement in Qxfo value is primarily attributed to the increase in uniform grain size and density. 相似文献
12.
The dielectric properties of c-axis epitaxial BaTiO3 thin film on LaAlO3 are investigated at frequencies of 0.5–30 GHz. For the measurements, interdigital capacitors with the Au/Ti electrode configurations of five fingers pairs that are 15 m wide and spaced 2 m apart are prepared by photolithography and lift-off patterning. Finger length varies from 20 to 80 m. The capacitance of epitaxial BaTiO3 films exhibited no frequency dependence up to 10 GHz with the exception of slightly upward tendency of capacitance in BaTiO3 film with a finger length of 80 m due to the self resonant frequency at 20 GHz. The Q-factors of the capacitors, defined as Q = 1/CR, are decreased up to 10 GHz with increased frequency. At 10 GHz, the BaTiO3 film has a tunability [defined as k(V) = [C(0)–C(V)]C(0)] of 1.5% at 15 V, a loss tangent of 0.2 at room temperature. The small tunability can be interpreted as a result of in-plane compressive stress of BaTiO3 film exhibiting large dielectric anisotropy. For the improvement of tunability and dielectric loss in the interdigital BaTiO3 capacitor, the tetragonality (c/a) of epitaxial BaTiO3 film and design of interdigital capacitor should be modified. 相似文献
13.
Processing Effects on the Microstructure and Dielectric Properties of Barium Strontium Titanate (BST) Ceramics 总被引:3,自引:0,他引:3
Barium Strontium Titanate (BST) ferroelectric thick films have been investigated as potential candidates for use in frequency agile microwave circuit devices. Powder processing techniques such as screen-printing have been used to make BST thick films. However, due to the interactions between the BST and substrates such as alumina, the sintering temperatures for the BST thick films are limited and the resultant films are difficult to achieve full densification. In this paper, the effects of different powder processing conditions (calcination, sintering temperature and time) on the sintering behaviour and dielectric properties of the BST ceramics have been investigated. The dielectric behaviour of the ceramics has been correlated with composition and microstructural features such as chemical homogeneity, grain size and domain wall movements. 相似文献
14.
Li2MgTiO4 (LMT) ceramics which are synthesized using a conventional solid-state reaction route. The LMT ceramic sintered at 1250°C for 4 h had good microwave dielectric properties. However, this sintering temperature is too high to meet the requirement of low-temperature co-fired ceramics (LTCC). In this study, the effects of B2O3 additives and sintering temperature on the microstructure and microwave dielectric properties of LMT ceramics were investigated. The B2O3 additive forms a liquid phase during sintering, which decreases the sintering temperature from 1250°C to 925°C. The LMT ceramic with 8 wt% B2O3 sintered at 925°C for 4 h was found to exhibit optimum microwave dielectric properties: dielectric constant 15.16, quality factor 64,164 GHz, and temperature coefficient of resonant frequency -28.07 ppm/°C. Moreover, co-firing of the LMT ceramic with 8 wt% B2O3 and 20 wt% Ag powder demonstrated good chemical compatibility. Therefore, the LMT ceramics with 8 wt% B2O3 sintered at 925°C for 4 h is suitable for LTCC applications. 相似文献
15.
16.
Ba(Ti1 –x
Sn
x
)O3 solid solutions were prepared by a solid state reaction method, and their dielectric and tunable characteristics were investigated together with the microstructures and diffused phase transition behaviors. The dielectric relaxation behaviors were observed and became stronger with increasing x.The obvious field dependence of the present system was observed with high dielectric constant and low loss at relatively lower DC electric field. The excellent tunable dielectric characteristics were achieved for x= 0.15 at room temperature: tunability 56%, tan 0.003 at 10 kHz under 7.6 kV/cm, indicating that it is a promising candidate for electric-field tunable dielectrics working at room temperature. 相似文献
17.
Co-modification of Ba5NdTi3Ta7O30 dielectrics ceramics was investigated through Pb substitution for Ba and introducing Bi4Ti3O12 secondary phase. The dielectric constant increased from 150 to 283, the temperature coefficient of the dielectric constant decreased from –2500 ppm/°C to –1279 ppm/°C, and the dielectric loss decreased to 0.0007 at 1 MHz. Meanwhile, the bi-phase ceramics were investigated to achieve temperature stable ceramics with high dielectric constant and low dielectric loss. As the composition x varied from 0.4 to 0.7 for (1 – x)(Ba0.8Pb0.2)5NdTi3Ta7O30/xBi4Ti3O12, the temperature coefficient of the dielectric constant changed from negative to zero to positive. 相似文献
18.
Pure aluminum nitride (AIN) has been successfully sintered to highly translucent form by microwave sintering at 1850°C with a dwelling time of 30–60 minutes. The results showed that the sintering temperature should be at least 1850°C or higher to get reasonable translucency in the AIN sample by the microwave sintering process. On the other hand, the conventional sintering method requires much longer sintering time to obtain a translucent AIN ceramics. 相似文献
19.
Pb(Yb1/2Nb1/2)O3-PbTiO3 ceramics at the morphotropic phase boundary (50:50) were sintered by conventional and reactive methods to 95% theoretical density and grain sizes <10 m. Excess PbO, added to enhance the densification, resulted in PbO-based non-ferroelectric phases that degraded the electrical properties. Volatilization of excess PbO by annealing the samples after sintering resulted in dense, perovskite samples and excellent electrical properties. The best electrical properties, obtained via reactive sintering, were a remanent polarization, P
r, of 0.36 C/m2, a maximum dielectric constant of 31,000 (at the T
c = 371°C and 1 kHz), a piezoelectric charge coefficient, d
33, of 508 pC/N, and an electromechanical coupling coefficient, k
33, of 0.61. 相似文献
20.
The microwave, near-millimetre and infrared (IR) dielectric response of Srn + 1TinO3n + 1 (n = 1–4) Ruddlesden-Popper homologous series was studied in the temperature range 10 to 300 K. Remarkable softening of the polar optical mode was observed in Sr4Ti3O10 and Sr5Ti4O13 which explains the increase in microwave permittivity and dielectric loss upon cooling. However, both samples have a distinct content of SrTiO3 dispersed between SrO layers. It is proposed therefore that the observed soft mode originates from the SrTiO3 microscopic inclusions. 相似文献