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1.
Butyl rubber–Ba(Zn 1/3Ta 2/3)O 3 (BR–BZT) composites and butyl rubber–silica (BRS) composites were prepared by sigma mixing. The dielectric properties at 1 MHz and 5 GHz of BR–BZT and BRS composites were investigated as a function of ceramic loading and were found to be improved with filler loading. For a optimum BZT loading of 0.26 v f, the BR–BZT composite have ε r = 4.88, tanδ = 0.0022 (at 5 GHz), coefficient of thermal expansion (CTE) = 112 ppm/°C, thermal conductivity (TC) = 0.30 Wm ?1 K ?1 and water absorption = 0.047 vol%. The BRS composites attained ε r = 2.79, tanδ = 0.0039 (at 5 GHz), CTE = 102 ppm/°C, TC = 0.40 Wm ?1 K ?1 and water absorption = 0.078 vol% for the same loading of silica. The stress–strain curves of both composites showed good flexibility of the composite. The measured relative permittivity and TC of both composites were compared with different theoretical approaches. 相似文献
2.
High dielectric constant and low loss (1 ? x) ZrTi 2O 6–xZnNb 2O 6 ceramic fillers have been prepared by the conventional solid-state reaction technique. Ceramic filled polytetrafluoroethylene (PTFE) microwave composite substrates were fabricated through the hot-pressing process. The microwave dielectric properties of (1 ? x) ZrTi 2O 6–xZnNb 2O 6/PTFE composites were measured using stripline resonator method. The relative dielectric constant ( ε r) and loss tangent (tan δ) of the composites increase with an increase of x in the (1 ? x) ZrTi 2O 6–xZnNb 2O 6 ceramic at an optimum filler loading of 46vol%. As the x in the (1 ? x) ZrTi 2O 6–xZnNb 2O 6 ceramic increase, the coefficient of thermal expansion and temperature coefficient of dielectric constant decrease. 0.55ZrTi 2O 6–0.45ZnNb 2O 6 filled PTFE composite exhibits a dielectric constant of 7.32 with a loss tangent of 0.0015 (10 GHz) and a temperature coefficient of dielectric constant of ?84 ppm/ oC at an optimum filler loading of 46 vol%. 相似文献
3.
Polytetrafluorethylene (PTFE) composites filled with perovskite (Ca,Li,Sm)TiO 3 (CLST) dielectric ceramic of various volume fractions filler up to 60% were prepared. The effects of volume fraction of ceramic filler on the microstructure and dielectric properties of the composites have been investigated. A comparative study of dielectric properties of experiment and modeling analysis has been carried out at high frequencies for the CLST/PTFE composites. The results indicate that both the dielectric constant and the dielectric loss increase with the filler. The CLST/PTFE composite with 40% ceramic has exhibited good dielectric properties: ε r?=?7.92 (~10 GHz), tan δ?=?1.2?×?10 ?3 (~10 GHz), and τ f?=??45 ppm/°C. The dielectric properties are obviously better than most composites reported previously at high frequencies in the aspects of dielectric loss and thermal stability. The dielectric constant and dielectric loss of composites predicted by the Rother–Lichtenecker equation and the general mixing model are in good agreement with the experiment data when the volume fraction of ceramic is less than 40%. When the volume fraction of the ceramic is more than 40%, the deviation occurs. By introducing the correction factor, the theoretical values of the dielectric constant agrees well with the experimental values. 相似文献
4.
The aqueous gelcasting-assisted solid-state method (AGAS) and traditional solid-state reaction method (TSSR) were used to prepare Ba[(Co 0.7Zn 0.3) 1/3Nb 2/3]O 3 (BCZN)-based ceramics. The effects of different powder-preparation methods on the microstructures and dielectric properties of the BCZN-based ceramics were investigated. X-ray diffraction analysis showed completely the same phase compositions regardless of the preparation method adopted. The relative permittivity ( ε r) did not significantly vary between the two methods. However, BCZN with CeO 2-added ceramics prepared by AGAS had higher and more uniform density (6.374 g/cm 3) and high quality factor of resonant frequency ( Q × f) value (75,843 GHz) than those prepared by TSSR because of the more uniform microstructures, as shown by scanning electron microscopy images. The temperature coefficients of resonant frequency ( τ f = 7.4 ppm/°C) of the ceramics prepared by AGAS were also closer to zero than those prepared by TSSR. 相似文献
5.
A new polymer-ceramic composite was prepared using PTFE and low loss Sr 2ZnSi 2O 7. The dielectric properties of the composite were studied in the microwave and radiofrequency ranges. The relative permittivity
(ε r) and dielectric loss (tan δ) increased with the filler loading from 0.10 to 0.50 volume fractions (v f). The observed values of ε r, thermal conductivity and coefficient of thermal expansion (CTE) were compared with the corresponding theoretical predictions.
The ability of the composite towards moisture absorption resistance was studied as a function of filler loading. It was also
found that the variation of ε r was less than 2% in the temperature range 25–90 °C, at 1 MHz. For a filler content of 0.50 v f, the PTFE/Sr 2ZnSi 2O 7 composite exhibited ε r = 4.4 , tan δ = 0.003 (at 4–6 GHz), CTE = 38.3 ppm/°C, thermal conductivity = 2.1 W/mK and moisture absorption = 0.09 wt%. 相似文献
6.
The xCaTiO 3–(1 ? x)Sm 0.9Nd 0.1AlO 3 (0.25 ≤ x ≤ 0.85) microwave dielectric ceramics were prepared by conventional solid state reaction method. The phase structures were characterized by X-ray diffraction, scanning electron microscope and Raman spectra. Solid solutions with the orthorhombic perovskite structure with octahedral tilting were formed from the x range of 0.25 to 0.85. Microwave dielectric properties of xCaTiO 3–(1 ? x)Sm 0.9Nd 0.1AlO 3 ceramics were investigated systematically. The optimum property of the ceramics was obtained for x = 0.65 sintered at 1,415 °C for 3 h: relative permittivity ε r = 39.70, Q × f = 50,012 GHz, τ f = ?6.8 ppm/°C. xCaTiO 3–(1 ? x)Sm 0.9Nd 0.1AlO 3 ceramics provide a new promising material for application in the microwave technology with relative permittivity lying within the range from 39 to 44, high quality factor and near-zero τ f . 相似文献
7.
Microwave (MW) dielectric ceramics based on the solid solution (1 ? x)CaTiO 3– x(Li 0.5Nd 0.5)TiO 3 (0.25 ≤ x ≤ 1.0) were prepared by conventional solid-state synthesis using the mixed oxide route. Compositions closest to zero τ f (+65 ppm/°C) were obtained at x = 0.8 where ε r = 110 and the microwave quality factor, Q f 0 ? 2600 GHz for samples sintered at 1300 °C. To reduce the sintering temperature and compensate for any Li 2O loss during fabrication, ≤0.5 wt% 0.5Li 2O–0.5B 2O 3 was added as a sintering aid in the form of raw oxides (LBR) and also as a pre-reacted glass (LBG). 0.5 wt% LBR was the most effective, reducing the temperature to achieve optimum density by ~50 °C with no significant deterioration of microwave properties (ε r = 115, τ f = +65 ppm/°C and Q f 0 ? 2500 GHz). The high permittivity and relatively low sintering temperatures (1250 °C) are ideal for the development of low cost ultra-small dielectric loaded antenna, assuming the system can be tuned closer to zero by fractionally increasing x. 相似文献
8.
Silicone rubber composites filled with Ba(Zn 1/3Ta 2/3)O 3 (BZT) were prepared by hot pressing and the effect of filler content on the microwave dielectric, mechanical and thermal properties as well as on moisture absorption were investigated. The observed relative permittivity ( ɛr) was compared with different theoretical models. Among the different theoretical models Jayasundere Smith and Modified Lichtenecker were in good agreement with experimental values of ɛr. The study of the mechanical property showed that the silicone rubber – BZT composites were flexible and stretchable. The coefficient of thermal expansion and specific heat capacity decreased whereas thermal conductivity, thermal diffusivity and the moisture absorption increased with increase in filler loading. 相似文献
9.
Polymer/Sr 2ZnSi 2O 7 (SZS) ceramic composites suitable for substrate applications have been developed using the polymers polystyrene (PS), high
density polyethylene (HDPE) and Di-Glycidyl Ether of Bisphenol A (DGEBA). The dielectric, thermal and mechanical properties
of the composites are investigated as a function of various concentrations of the ceramic filler. The obtained values of relative
permittivity, dielectric loss tangent, thermal conductivity and coefficient of thermal expansion of the composites are compared
with the corresponding theoretical predictions. The relative permittivity of the polymer/ceramic composites increases with
filler loading. The dielectric loss tangent also shows the same trend except for DGEBA/SZS composites. The major advantages
of the ceramic loading are improvement in thermal conductivity and a decrease in the coefficient of thermal expansion. The
tensile strength of the composites decreases with increase in filler content, whereas an improvement is observed in microhardness.
The variation of relative permittivity (at 1 MHz) of the composites is also studied as a function of temperature. 相似文献
10.
The phase composition and microwave dielectric properties of Mg-excess MgTiO 3 (Mg/Ti = 1, 1.02, 1.04, 1.05, 1.07) ceramics prepared via the conventional solid-state reaction route were investigated. A slight deviation from stoichiometry does not practically affect the relative permittivity and temperature coefficient of resonant frequency of the specimen. However, the Q f value is very sensitive to the composition and it shows a non-linear variation corresponding to a relative amount of Mg. A very high Q f can be achieved for specimen with single MgTiO 3 phase, which can be obtained within the suitable composition. As the increasing of Mg content, the MgTi 2O 5 phase which was derived from Mg/Ti = 1 was disappeared, and when it exceeded 1.02, the phase of Mg 2TiO 4 emerged. Along with the augmentation of Mg/Ti, the bulk density and Q f showed an initial increase, followed by a decrease, but ε r had been declining. The specimen with single MgTiO 3 phase was obtained at the level of Mg/Ti = 1.02. A high Q f of 357,400 GHz (at 10 GHz) together with an ε r = 17 and τ f = ?51 ppm/°C for MgTiO 3 ceramics (Mg/Ti = 1.02) were obtained at 1,390 °C sintered for 4 h. 相似文献
11.
A novel microwave dielectric ceramics Li 2Mg 2(WO 4) 3 (LMW) for low-temperature co-fired ceramics (LTCC) application were prepared by the conventional solid-state sintering method. Densification, phases, microstructure and microwave dielectric properties of the Li 2Mg 2(WO 4) 3 ceramics were investigated. The optimal sintering temperature of dense Li 2Mg 2(WO 4) 3 ceramic approximately ranges from 825 to 875 °C for 3 h. The ceramic specimens fired at 875 °C for 3 h exhibits excellent microwave dielectric properties: ε r = 7.72, Q × f = 29,600 GHz ( f = 6.0 GHz), and τ f = ?15.5 ppm/°C. Moreover, the Li 2Mg 2(WO 4) 3 ceramics has a chemical compatibility with Ag during cofiring, which makes it a promising ceramic for LTCC technology application. 相似文献
12.
(1 ? y)[0.5ZnNb 2O 6–0.5Zn 3Nb 2O 8]– yZnTa 2O 6 with y = 0.91 (ZNT) ceramic have been prepared by conventional solid state ceramic route. The effect of glass additives on the microstructure, densification, and microwave dielectric properties of the ZNT ceramic for low temperature co-fired ceramic applications was investigated. Different weight percentages of quenched glass such as ZnO–B 2O 3–SiO 2, BaO–B 2O 3–SiO 2, LiO–B 2O 3–SiO 2 and MgO–B 2O 3–SiO 2 were added to ZNT powder. The crystal structure of the ceramic–glass composites was studied by X-ray diffraction and microstructure by scanning electron microscopy. The microwave dielectric properties such as relative permittivity (ε r), quality factor (Q uxf) and co-efficient of temperature variation of resonant frequency (τ f) of the ceramics have been measured in the frequency range 4–6 GHz. The 5 wt% ZnO–B 2O 3–SiO 2 added ZNT ceramic sintered at 900 °C showed: ε r = 28.1, Q uxf = 32820 GHz (at 4.92 GHz), and τ f = ?7.7 ppm/ oC respectively. 相似文献
13.
In the present work, a novel MgAl 2Ti 3O 10 ceramic was obtained using a traditional solid-state reaction method. X-ray diffraction and energy dispersive spectrometer showed that the main MgAl 2Ti 3O 10 phase was formed after sintered at 1300–1450 °C. With rising the sintering temperature from 1300 to 1450 °C, the bulk density ( ρ), relative permittivity ( ε r ) and Q?×? f value firstly increased, reached the maximum values (3.61 g/cm 3, 14.9, and 26,450 GHz) and then decreased. The temperature coefficient of resonator frequency ( τ f ) showed a slight change at a negative range of ??94.6 to ??83.7 ppm/°C. When the sintering temperature was 1400 °C, MgAl 2Ti 3O 10 ceramics exhibited the best microwave dielectric properties with Q?×? f?=?26,450 GHz, ε r ?=?14.9 and τ f ?=???83.7 ppm/°C. 相似文献
14.
High dielectric materials have gained an important position in microwave electronics by reducing the size and cost of components for a wide range of applications from mobile telephony to spatial communications. Ba(Zn 1/3Ta 2/3)O 3 (BZT) is an A(B′B″)O 3 type perovskite material, showing ultra high values of the quality factor Q. Ceramic-based BZT dielectric materials were prepared by solid state reaction. The samples were sintered at temperatures in the range 1400 ÷ 1600 °C for 4 h. Compositional, structural and morphological characterization were performed by using XRD, SEM and EDX analysis. The dielectric properties were measured in the microwave range (6 ÷ 7 GHz). An additional annealing at 1400 °C for 10 h has improved some dielectric parameters. For samples sintered at temperatures higher than 1500 °C, the permittivity values were obtained in the interval 30 ÷ 35 and almost do not change the value after the annealing. The Q × f product substantially increases up to about 135,000 GHz, exhibiting a low temperature coefficient of the resonant frequency ( τf) in microwaves. The best parameters were obtained for the samples sintered at 1600 °C with additional annealing. The achieved high values of the Q × f product recommend these materials for microwave and millimeter wave applications. 相似文献
15.
Crystal structure and dielectric properties of Zn 3Mo 2O 9 ceramics prepared through a conventional solid-state reaction method were characterized. XRD and Raman analysis revealed that the Zn 3Mo 2O 9 crystallized in a monoclinic crystal structure and reminded stable up to1020 °C. Dense ceramics with high relative density (~ 92.3%) were obtained when sintered at 1000 °C and possessed good microwave dielectric properties with a relative permittivity ( ε r ) of 8.7, a quality factor ( Q?×? f) of 23,400 GHz, and a negative temperature coefficient of resonance frequency ( τ f ) of around ??79 ppm/°C. With 5 wt% B 2O 3 addition, the sintering temperature of Zn 3Mo 2O 9 ceramic was successfully lowered to 900 °C and microwave dielectric properties with ε r ?=?11.8, Q?×? f?=?20,000 GHz, and τ f = ??79.5 ppm/°C were achieved. 相似文献
16.
Li 2ZnTi 3O 8 (LZT) microwave dielectric ceramics prepared by reaction-sintering process were investigated. Li 2CO 3, ZnO and TiO 2 powders were mixed, pressed and sintered directly into ceramic pellets without any calcination stage involved. Pure LZT phase was obtained after sintering at temperatures above 1,100 °C for 2 h. LZT ceramic with the maximum bulk density of 3.81 g/cm 3 (96.2 % of the theoretical value) and excellent microwave dielectric properties of ? r = 25.8, Q × f = 78,216 GHz and τ f = ?10.5 ppm/°C was obtained after sintering at 1,100 °C for 2 h. The results show that the reaction-sintering process is a simple and effective method to produce LZT ceramics. 相似文献
17.
Lead-free 0.5Ba(Zr xTi 1?x)O 3–0.5(Ba 0.75Ca 0.25)TiO 3 (x = 0.25, 0.30, 0.35, 0.40) ceramics have been synthesized by a conventional solid state sintering method. The room temperature ferroelectric and electrostrictive properties of these ceramics were studied. Based on the measured properties, these ceramics showed a typical relaxor behavior. The Curie temperature of BZT–BCT ceramics decreases with increasing the Zr content. The largest electrostrictive strain and electrostrictive coefficient are founded in BZT–BCT ceramic with x = 0.25, the value is 0.16 % and 0.079 m 4 C ?2, respectively. The polarization, electrostrictive strain and electrostrictive coefficient ( Q 11) decrease with increase in Zr concentration. For samples with low Curie temperature, which have large room temperature dielectric constant ( ε), electrostrictive coefficient increases ( Q 11) is smaller. Because doping can disrupt the long range cation order, and electrostrictive ( Q 11) coefficient increases with cation order from disordered, through partially-ordered, simple relaxor and then ordered perovskites, ferroelectrics with a disordered structure have a huge permittivity, but a small electrostrictive coefficient ( Q 11). 相似文献
18.
(1 ? x) Ca(Zn 1/3Nb 2/3) O 3 ? xBa(Zn 1/3Nb 2/3)O 3 (short for CZN/BZN, x = 0–1.0) ceramics were prepared and investigated through the “one-step synthesis method” method. The structure of the system was analyzed using X-ray diffraction. The microstructure of the sintered pellet was analyzed using scanning electron microscopy. Dielectric constant (ε r), temperature coefficient of resonant frequency (τ f) and the unloaded quality factor (Q × f) were measured in the microwave frequency region. Two dielectric properties were firstly in the rising tendency and then decreasing with the increased x. On the other hand, a good combination of microwave dielectric properties (ε r = 24, Q × f = 23,510 GHz τ f = ?9 ppm/°C) were obtained at x = 0.1. The compositions have excellent microwave dielectric properties and hence are suitable for ceramic capacitors or dielectric resonators applications. 相似文献
19.
Ba(Mg1/3Nb2/3)O3–MgO composite ceramics were prepared by solid-phase method. The ceramic exhibited the 1:2 ordered structure. By adding a proper amount of MgO, the permittivity decreased rapidly compared with other Ba(Mg1/3Nb2/3)O3-based ceramics. The Q?×?f values of the samples were greatly improved by nano-silica. Raman spectra showed that the permittivity and Q?×?f value showed a strong correlation with Raman shift and full width at half maximum of the A1g(O) phonon mode, respectively. The Raman shift of A1g(O) was consistent with the variation trend of permittivity. And the full width at half maximum of the A1g(O) phonon mode had a negative correlation with the Q?×?f value. The results showed that upon adding 1.5 wt% nano-silica to the ceramics, the ceramics sintered at 1550 °C for 5 h had the lowest Raman shift and the narrowest full width at half maximum, achieving the best microwave dielectric properties: εr?=?22.22, Q?×?f?=?80,436 GHz, τf?=?–?5.89 ppm/°C. 相似文献
20.
A novel microwave dielectric ceramics Bi(Sc 1/3Mo 2/3)O 4 with low firing temperature were prepared via the solid reaction method. The specimens have been characterized using scanning electron microscopy, X-ray diffraction, Raman spectroscopy and DC conductivity. The Bi(Sc 1/3Mo 2/3)O 4 ceramics showed B-site ordered Scheelite-type structure with space group C2/c. Raman analysis indicated that prominent bands were attributed to the normal modes of vibration of MoO 4 2? tetrahedra. The dielectric loss of Bi(Sc 1/3Mo 2/3)O 4 ceramics can be depended strongly the bulk conductivity by DC measurement. The superior microwave dielectric properties are achieved in the Bi(Sc 1/3Mo 2/3)O 4 ceramic sintered at 875 °C/4 h, with dielectric constant?~?25, Q?×? f ~?51,716 GHz at 6.4522 GHz and temperature coefficient of resonance frequency ~???70.4 ppm/°C. It is a promising microwave dielectric material for low-temperature co-fired ceramics technology. 相似文献
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