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1.
Rock-salt-structured Li2MgTiO4 ceramic was prepared by the conventional mixed oxide route and its microwave dielectric properties were investigated. The microstructures of the ceramics were characterized by SEM. The dielectric properties of the ceramics exhibited a significant dependence on the sintering condition and crystal structure. A new microwave dielectric material, Li2MgTiO4 sintered at 1360 °C has a dielectric constant (?r) of ∼17.25, a Q × f of ∼97,300 GHz (where f = 9.86 GHz, is the resonant frequency) and a τf of ∼-27.2 ppm/°C. The microwave dielectric properties of the ceramic are reported for the first time.  相似文献   

2.
The phases, microstructure and microwave dielectric properties of ZnTiNb2O8-xTiO2 composite ceramics with different weight percentages of BaCu(B2O5) additive prepared by solid-state reaction method have been investigated using the X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The results showed that the microwave dielectric properties were strongly dependent on densification, grain sizes and crystalline phases. The sintering temperature of ZnTiNb2O8 ceramics was reduced from 1250 °C to 950 °C by doping BaCu(B2O5) additive and the temperature coefficient of resonant frequency (τf) was adjusted from negative value of −52 ppm/°C to 0 ppm/°C by incorporating TiO2. Addition of 2 wt% BaCu(B2O5) in ZnTiNb2O8-xTiO2 (x = 0.8) ceramics sintered at 950 °C showed excellent dielectric properties of ?r = 38.89, Q × f = 14,500 GHz (f = 4.715 GHz) and τf = 0 ppm/°C, which represented very promising candidates as LTCC dielectrics for LTCC applications.  相似文献   

3.
Microstructure and microwave dielectric properties of Mg-substituted ZnNb2O6-TiO2 microwave ceramics were investigated. Mg acted as a grain refining reagent and columbite phase stabilization reagent. With an increasing Mg content, the amount of ixiolite (Zn, Mg) TiNb2O8 decreased, and the amount of (Zn0.9Mg0.1)0.17Nb0.33Ti0.5O2 and columbite increased. ZnO-Nb2O5-1.75TiO2-5 mol.%MgO exhibited excellent dielectric properties (at 950 °C): ?r = 35.6, Q × f = 16,000 GHz (at 5.6 GHz) and τf = −10 ppm/°C. The material was applied successfully to make RF/microwaves ceramic capacitor, whose self-resonance frequency was 19 GHz at low capacitance of 0.13 pF.  相似文献   

4.
The behavior of dielectric and microwave properties against sintering temperature has been carried out on CaO-SiO2-B2O3 ceramic matrix composites with ZrO2 addition. The results indicated that ZrO2 addition was advantageous to improve the dielectric and microwave properties. X-ray diffraction (XRD) patterns show that the major crystalline β-CaSiO3 and a little SiO2 phase existed at the temperature ranging from 950 °C to 1050 °C. At 0.5 wt% ZrO2, CaO-SiO2-B2O3 ceramic matrix composites sintered at 1000 °C possess good dielectric properties: ?r = 5.85, tan δ = 1.59 × 10−4 (1 MHz) and excellent microwave properties: ?r = 5.52, Q · f = 28,487 GHz (11.11 GHz). The permittivity of Zr-doped CaO-SiO2-B2O3 ceramic matrix composites exhibited very little temperature dependence, which was less than ±2% over the temperature range of −50 to 150 °C. Moreover, the ZrO2-doped CaO-SiO2-B2O3 ceramic matrix composites have low permittivity below 5.5 over a wide frequency range from 20 Hz to 1 MHz.  相似文献   

5.
The effects of BaCu(B2O5) additives on the sintering temperature and microwave dielectric properties of (Mg0.7Zn0.3)0.95Co0.05TiO3 ceramics were investigated. The (Mg0.7Zn0.3)0.95Co0.05TiO3 ceramics were not able to be sintered below 1000 °C. However, when BaCu(B2O5) were added, they were sintered below 1000 °C and had the good microwave dielectric properties. It was suggested that a liquid phase with the composition of BaCu(B2O5) was formed during the sintering and assisted the densification of the (Mg0.7Zn0.3)0.95Co0.05TiO3 ceramics at low temperature. BaCu(B2O5) powders were produced and used to reduce the sintering temperature of the (Mg0.7Zn0.3)0.95Co0.05TiO3 ceramics. Good microwave dielectric properties of Q × f = 35,000 GHz, ?r = 18.5.0 and τf = −51 ppm/°C were obtained for the (Mg0.7Zn0.3)0.95Co0.05TiO3 ceramics containing 7 wt.% mol% BaCu(B2O5) sintered at 950 °C for 4 h.  相似文献   

6.
The Li2ZnxCo1−xTi3O8 (x = 0.2-0.8) solid solution system has been synthesized by the conventional solid-state ceramic route and the effect of Zn substitution for Co on microwave dielectric properties of Li2CoTi3O8 ceramics has also been investigated. The microwave dielectric properties of these ceramics show a linear variation between the end members for all compositions. The optimized sintering temperatures of Li2ZnxCo1−xTi3O8 ceramics increase with increasing content of Zn. The specimen with x = 0.4 sintered at 1050 °C/2 h exhibits an excellent combination of microwave dielectric properties with ?r = 27.7, Qu × f = 57,100 GHz and τf = −1.0 ppm/°C.  相似文献   

7.
(1 − x)ZnMoO4-xTiO2 (x = 0.0, 0.05, 0.158, 0.25, and 0.35) composite ceramics were synthesized by the conventional solid state reaction process. The sintering behavior, phase composition, chemical compatibility with silver, and microwave dielectric properties were investigated. All the specimens can be well densified below 950 °C. From the X-ray diffraction analysis, it indicates that the triclinic wolframite ZnMoO4 phase coexists with the tetragonal rutile TiO2 phase, and it is easy for silver to react with ZnMoO4 to form Ag2Zn2(MoO4)3 phase and hard to react with TiO2. When the volume fraction of TiO2 (x value) increasing from 0 to 0.35, the microwave dielectric permittivity of the (1 − x)ZnMoO4-xTiO2 composite ceramics increases from 8.0 to 25.2, the Qf value changes in the range of 32,300-43,300 GHz, and the temperature coefficient τf value varies from −128.9 to 157.4 ppm/°C. At x = 0.158, the mixture exhibits good microwave dielectric properties with a ?r = 13.9, a Qf = 40,400 GHz, and a τf = +2.0 ppm/°C.  相似文献   

8.
This study investigated the potential applications of microwave dielectric properties of Mg2SnO4 ceramics in mobile communication. Mg2SnO4 ceramics were prepared using a conventional solid-state method. The X-ray diffraction patterns of the Mg2SnO4 ceramics revealed no significant variation of phase with sintering temperature. A maximum density of 4.62 g/cm3, a dielectric constant (?r) of 8.41, a quality factor (Q × f) of 55,100 GHz, and a temperature coefficient of resonant frequency (τf) of −62 ppm/ °C were obtained when Mg2SnO4 ceramics were sintered at 1550 °C for 4 h.  相似文献   

9.
Microwave dielectric properties and microstructures of (Mg0.95Co0.05)TiO3 ceramics prepared by a new sintering method (reaction-sintering method) were investigated. A pure phase of (Mg0.95Co0.05)TiO3 was obtained by the new method and excellent dielectric properties were observed due to uniformities of the microstructure and the phase. In contrast, the secondary phase (Mg0.95Co0.05)Ti2O5 was observed in samples prepared by conventional sintering method. In order to study the influence of secondary phase on the microwave dielectric properties quantitatively, the weight fraction of (Mg0.95Co0.05)Ti2O5 was calculated on the basis of Rietveld refinement. The pore-free?r values of specimens prepared by two different methods indicated that porosity plays an important role in the ?r values of (Mg0.95Co0.05)TiO3 ceramics. Specimens sintered by reaction-sintering method at 1350 °C for 4 h possess excellent dielectric properties with an ?r of 16.3, a Q × f value of 244,500 GHz, and a τf value of −53.5 ppm/°C.  相似文献   

10.
The effect of H3BO3-CuO-Li2CO3 combined additives on the sintering temperature, microstructure and microwave dielectric properties of (Ca0.61Nd0.26) (Ti0.98Sn0.02)O3 (CNTS) ceramics was investigated. The H3BO3-CuO-Li2CO3 combined additives lowered the sintering temperature of CNTS ceramics effectively from 1300 to 950 °C. This may be due to the interim liquid-phase of Li2O-CuO-B2O3, which were formed in the sintering process. (Li0.5Nd0.5)TiO3 (LNT) demonstrated an effective compensation in τf value of the low-fired CNTS ceramics. The 0.4CNTS-0.6LNT ceramics with 5 wt% (H3BO3-CuO)-0.5 wt% Li2CO3 sintered at 900 °C for 2 h shows excellent dielectric properties: ?r = 90.6, Q × f = 3400 GHz, and τf = 9 ppm/°C. Also, the LTCC material is compatible with Ag electrode.  相似文献   

11.
The microwave dielectric properties of La(Mg0.5−xNixSn0.5)O3 ceramics were examined with a view to their exploitation for mobile communication. The La(Mg0.5−xNixSn0.5)O3 ceramics were prepared by the conventional solid-state method at various sintering temperatures. The X-ray diffraction patterns of the La(Mg0.4Ni0.1Sn0.5)O3 ceramics revealed no significant variation of phase with sintering temperatures. Apparent density of 6.71 g/cm3, dielectric constant (?r) of 20.19, quality factor (Q × f) of 74,600 GHz, and temperature coefficient of resonant frequency (τf) of −85 ppm/°C were obtained for La(Mg0.4Ni0.1Sn0.5)O3 ceramics that were sintered at 1550 °C for 4 h.  相似文献   

12.
The microwave dielectric properties and microstructures of (1 − x)La(Mg0.5Ti0.5)O3-x(Ca0.8Sr0.2)TiO3 ceramics, prepared by a mixed oxide route, have been investigated. The forming of solid solutions was confirmed by the XRD patterns and the measured lattice parameters for all compositions. A near zero τf was achieved for samples with x = 0.5, although the dielectric properties varied with sintering temperature. The Q × f value of 0.5La(Mg0.5Ti0.5)O3-0.5(Ca0.8Sr0.2)TiO3 increased up to 1475 °C, after which it decreased. The decrease in dielectric properties was coincident with the onset of rapid grain growth. The optimum combination of microwave dielectric properties was achieved at 1475 °C for samples where x = 0.5 with a dielectric constant ?r of 47.12, a Q × f value of 35,000 GHz (measured at 6.2 GHz) and a τf value of −4.7 ppm/°C.  相似文献   

13.
Composite ceramics in the solid solution of Zrx(Zn1/3Nb2/3)1−xTiO4 (x = 0.1-0.4) have been prepared by the mixed oxide route. Formation of solid solution was confirmed by the X-ray diffraction patterns. The microwave dielectric properties, such as dielectric constant (?r), Q × f value and temperature coefficient of resonant frequency (τf) have been investigated as a function of composition and sintering temperature. With x increasing from 0.1 to 0.4, the dielectric constant decreases from 70.9 to 43.2, and the τf decreases from 105 to 55 ppm/°C. The Q × f value, however, increases with increasing x value to a maximum 26,600 GHz (at 6 GHz) at x = 0.3, and then decreases thereafter. For low-loss microwave applications, a new microwave dielectric material Zr0.3(Zn1/3Nb2/3)0.7TiO4, possessing a fine combination of microwave dielectric properties with a high ?r of 51, a high Q × f of 26,600 GHz (at 6 GHz) and a τf of 70 ppm/°C, is suggested.  相似文献   

14.
Phase evolution and microwave dielectric properties of (1 − x)(Mg0.95Co0.05)2TiO4-xTiO2 (x = 0-1) ceramics prepared by the conventional mixed oxide route have been investigated. Increasing the TiO2 content would lead to a main phase transformation from (Mg0.95Co0.05)2TiO4 to (Mg0.95Co0.05)TiO3, (Mg0.95Co0.05)Ti2O5 and then TiO2. Not only did the TiO2 addition compensate the τf, it also lowered the sintering temperature of specimen. A huge drop of Q × f occurs at a 40-60 mol% TiO2 addition was attributed to the formation of (Mg0.95Co0.05)Ti2O5 phase. Specimen with x = 0.78 can possess an excellent combination of microwave dielectric properties: ?r ∼ 24.77, Q × f ∼ 38,500 GHz and τf ∼ −1.3 ppm/°C.  相似文献   

15.
The microwave dielectric properties of CaTiO3-added Mg2(Ti0.95Sn0.05)O4 ceramics prepared by the mixed oxide route have been investigated. The combination of spinel-structured Mg2(Ti0.95Sn0.05)O4 and perovskite-structured CaTiO3 forms a two-phase system (1 − x)Mg2(Ti0.95Sn0.05)O4-xCaTiO3, which was confirmed by the XRD patterns and the EDX analysis and it also leads to a zero τf. The microwave dielectric properties of the ceramics can be effectively controlled by varying the x value. For practical applications, a new microwave dielectric material 0.91Mg2(Ti0.95Sn0.05)O4-0.09CaTiO3 is suggested and it possesses a good combination of dielectric properties with an ?r of ∼18.01, a Q × f of ∼92,000 GHz, and a τf of ∼0 ppm/°C, which makes it is a very promising candidate material for high frequency applications.  相似文献   

16.
The crystal structures, phase compositions and the microwave dielectric properties of the xLa(Mg1/2Ti1/2)O3-(1 − x)Ca0.8Sr0.2TiO3 composites prepared by the conventional solid state route have been investigated. The formation of solid solution is confirmed by the XRD patterns. Doping with B2O3 (0.5 wt.%) can effectively promote the densification and the dielectric properties of xNd(Mg1/2Ti1/2)O3-(1 − x)Ca0.6La0.8/3TiO3 ceramics. It is found that xNd(Mg1/2Ti1/2)O3-(1 − x)Ca0.6La0.8/3TiO3 ceramics can be sintered at 1375 °C, due to the liquid phase effect of B2O3 addition observed by Scanning Electronic Microscopy. At 1375 °C, 0.4Nd(Mg1/2Ti1/2)O3-0.6Ca0.6La0.8/3TiO3 ceramics with 1 wt.% B2O3 addition possesses a dielectric constant (?r) of 49, a Q × f value of 13,000 (at 8 GHz) and a temperature coefficients of resonant frequency (τf) of 1 ppm/°C. As the content of Nd(Mg1/2Ti1/2)O3 increases, the highest Q × f value of 20,000 GHz for x = 0.9 is achieved at the sintering temperature 1400 °C.  相似文献   

17.
The influence of Zr substitution for Ti on the microwave dielectric properties and microstructures of the Mg(ZrxTi1−x)O3(MZxT) (0.01 ≤ x ≤ 0.3) ceramics was investigated. The quality factors of Mg(ZrxTi1−x)O3 ceramics with x = 0.01-0.05 were improved because the solid solution of a small amount of Zr4+ substitution in the B-site could increase density and grain size. An excess of Zr4+ resulted in the formation of a great deal of secondary phase that declined the microwave dielectric properties of MZxT ceramics. The temperature coefficient of resonant frequency (τf) of Mg(ZrxTi1−x)O3 ceramics slightly increased with increasing Zr content, and the variation in τf was attributed to the formation of secondary phases.  相似文献   

18.
The crystal structure and the dielectric properties of (1 − x)La(Mg0.5Ti0.5)O3-xCa0.8Sm0.4/3TiO3 ceramics have been investigated. Ca0.8Sm0.4/3TiO3 was employed as a τf compensator and was added to La(Mg0.5Ti0.5)O3 to achieve a temperature-stable material. The formation of (1 − x)La(Mg0.5Ti0.5)O3-xCa0.8Sm0.4/3TiO3 solid solutions were confirmed by the XRD results and the measured lattice parameters for all compositions. The dielectric properties are strongly correlated to the sintering temperature and the compositional ratio of the specimens. Although the ?r of the specimen could be boosted by increasing the amount of Ca0.8Sm0.4/3TiO3, it would instead render a decrease in the Q × f. The τf value is strongly correlated to the compositions and can be controlled by the existing phases. A new microwave dielectric material 0.45La(Mg0.5Ti0.5)O3-0.55Ca0.8Sm0.4/3TiO3, possessing a fine combination of microwave dielectric properties with an ?r of 47.83, a Q × f of 26,500 GHz (at 6.2 GHz) and a τf of −1.7 ppm/°C, is proposed as a very promising candidate material for today's 3G applications.  相似文献   

19.
Ba(Zn1/3Ta2/3)O3 (BZT) dielectric resonators were prepared by solid-state reaction. The starting materials were BaCO3, ZnO, and Ta2O5 powders with high purity. The double calcined BZT pellets were sintered in air at temperatures of 1575, 1600, 1625, and 1650 °C for 4 h. The X-ray diffraction data allowed the study of the unit cell distortion degree and the presence of the secondary phases. A long-range order with a 2:1 ratio of Ta and Zn cations on the octahedral positions of the perovskite structure was observed with the increase of the sintering temperature. The dielectric constant of BZT resonators measured around 6 GHz was between 26 and 28. High values of Q × f product (120 THz) were obtained for BZT resonators sintered at 1650 °C/4 h. The temperature coefficient of the resonance frequency exhibits positive values less than 6 ppm/°C. The achieved dielectric parameters recommend BZT dielectric resonators for microwave and millimeter wave applications.  相似文献   

20.
The effects of K2O and Li2O-doping (0.5, 0.75 and 1.5 mol%) of Fe2O3/Cr2O3 system on its surface and the catalytic properties were investigated. Pure and differently doped solids were calcined in air at 400-600 °C. The formula of the un-doped calcined solid was 0.85Fe2O3:0.15Cr2O3. The techniques employed were TGA, DTA, XRD, N2 adsorption at −196 °C and catalytic oxidation of CO oxidation by O2 at 200-300 °C. The results revealed that DTA curves of pure mixed solids consisted of one endothermic peak and two exothermic peaks. Pure and doped mixed solids calcined at 400 °C are amorphous in nature and turned to α-Fe2O3 upon heating at 500 and 600 °C. K2O and Li2O doping conducted at 500 or 600 °C modified the degree of crystallinity and crystallite size of all phases present which consisted of a mixture of nanocrystalline α- and γ-Fe2O3 together with K2FeO4 and LiFe5O8 phases. However, the heavily Li2O-doped sample consisted only of LiFe5O8 phase. The specific surface area of the system investigated decreased to an extent proportional to the amount of K2O and Li2O added. On the other hand, the catalytic activity was found to increase by increasing the amount of K2O and Li2O added. The maximum increase in the catalytic activity, expressed as the reaction rate constant (k) measured at 200 °C, attained 30.8% and 26.5% for K2O and Li2O doping, respectively. The doping process did not modify the activation energy of the catalyzed reaction but rather increased the concentration of the active sites without changing their energetic nature.  相似文献   

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