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1.
The effect of CaO-SiO2-B2O3 (CSB) glass addition on the sintering temperature and dielectric properties of BaxSmyTi7O20 ceramics has been investigated using X-ray diffraction, scanning electron microscopy and differential thermal analysis. The CSB glass starts to melt at about 970 °C, and a small amount of CSB glass addition to BaxSmyTi7O20 ceramics can greatly decrease the sintering temperature from about 1350 to about 1260 °C, which is attributed to the formation of liquid phase. It is found that the dielectric properties of BaxSmyTi7O20 ceramics are dependent on the amount of CSB glass and the microstructures of sintered samples. The product with 5 wt% CSB glass sintered at 1260 °C is optimal in these samples based on the microstructure and the properties of sintering product, when the major phases of this material are BaSm2Ti4O12 and BaTi4O9. The material possesses excellent dielectric properties: ?r = 61, tan δ = 1.5 × 10−4 at 10 GHz, temperature coefficient of dielectric constant is −75 × 10−6 °C−1.  相似文献   

2.
The microwave dielectric properties and the microstructures of MgNb2O6 ceramics with CuO additions (1-4 wt.%) prepared with conventional solid-state route have been investigated. The sintered samples exhibit excellent microwave dielectric properties, which depend upon the liquid phase and the sintering temperature. It is found that MgNb2O6 ceramics can be sintered at 1140 °C due to the liquid phase effect of CuO addition. At 1170 °C, MgNb2O6 ceramics with 2 wt.% CuO addition possesses a dielectric constant (εr) of 19.9, a Q×f value of 110,000 (at 10 GHz) and a temperature coefficient of resonant frequency (τf) of −44 ppm/°C. The CuO-doped MgNb2O6 ceramics can find applications in microwave devices requiring low sintering temperature.  相似文献   

3.
The 0.83ZnAl2O4-0.17TiO2 (ZAT) ceramics were synthesized by solid state ceramic route. The effect of 27B2O3-35Bi2O3-6SiO2-32ZnO (BBSZ) glass on the microwave dielectric properties of ZAT was investigated. The crystal structure and the microstructure of the ceramic-glass composites were studied by X-ray diffraction and scanning electron microscopic techniques. The low frequency dielectric loss was measured at 1 MHz. The dielectric properties of the sintered samples were measured in the microwave frequency range by the resonance method. Addition of 0.2 wt% of BBSZ improved the dielectric properties with quality factor (Qu × f) > 120,000 GHz, temperature coefficient of resonant frequency (τf) = −7.3 ppm/°C and dielectric constant (?r) = 11.7. Addition of 10 wt% of BBSZ lowered the sintering temperature to about 950 °C with Qu × f > 10,000 GHz, ?r = 10 and τf = −23 ppm/°C. The reactivity of 10 wt% BBSZ added ZAT with silver was also studied. The results show that ZAT doped with suitable amount of BBSZ glass is a possible material for low-temperature co-fired ceramic (LTCC) application.  相似文献   

4.
Ba4MgTi11O27 microwave dielectric ceramic was investigated using X-ray diffraction, scanning electron microscopy and dielectric measurement. The pure Ba4MgTi11O27 ceramic shows a high sintering temperature (∼1275 °C) and good microwave dielectric properties as Q × f of 19,630 GHz, ?r of 36.1, τf of 14.6 ppm/°C. It was found that the addition of BaCu(B2O5) (BCB) can effectively lower the sintering temperature from 1275 to 925 °C, and does not induce much degradation of the microwave dielectric properties. The BCB-doped Ba4MgTi11O27 ceramics can be compatible with Ag electrode, which makes it a promising ceramic for LTCC technology application.  相似文献   

5.
The (0 0 l) textured BaBi2(Nb1 − xVx)2O9 (where x = 0, 0.03, 0.07, 0.1 and 0.13) ceramics were fabricated via the conventional melt-quenching technique followed by high temperature heat-treatment (800-1000 °C range). The influence of vanadium content and sintering temperature on the texture development and relative density were investigated. The samples corresponding to the composition x = 0.1 sintered at 1000 °C for 10 h exhibited the maximum orientation of about 67%. The Scanning electron microscopic studies revealed the presence of platy grains having the a-b planes perpendicular the pressing axis. The dielectric constant and the pyroelectric co-efficient values in the direction perpendicular to the pressing axis were higher. The anisotropy in the dielectric constant is about 100 (at 100 kHz) at the dielectric maximum temperature and anisotropy in the pyroelectric co-efficient is about 50 μC cm−2 °C−1 in the vicinity of pyroelectric anomaly for the sample corresponding to the composition x = 0.1 sintered at 1000 °C. Higher values of the dielectric loss and electrical conductivity were observed in the direction perpendicular to the pressing axis which is attributed to the high oxygen ion conduction in the a-b planes.  相似文献   

6.
Using solid-state reaction method, Zr2WP2O12 powder was synthesized for this study. The optimum heating condition was 1200 °C for 4 h. The obtained powder was compacted and sintered. The relative density of the Zr2WP2O12 ceramics with no sintering additive was 60%. That of samples sintered with more than 0.5 mass% MgO was about 97%. The average grain size (D50), as estimated from the polished surface of a sample sintered at 1200 °C for 4 h was about 1 μm. The obtained ceramics showed a negative thermal expansion coefficient of about −3.4 × 10−6 °C−1. Young's modulus, Poisson's ratio, three-point bending strength, Vickers microhardness, and fracture toughness of the obtained ceramics were, respectively, 74 GPa, 0.25, 113 ± 13 MPa, 4.4 GPa and 2.3 MPa m1/2.  相似文献   

7.
Glasses with the compositions of xLi2O-(70 − x)Nb2O5-30P2O5, x = 30-60, and their glass-ceramics are synthesized using a conventional melt-quenching method and heat treatments in an electric furnace, and Li+ ion conductivities of glasses and glass-ceramics are examined to clarify whether the glasses and glass-ceramics prepared have a potential as Li+ conductive electrolytes or not. The electrical conductivity (σ) of the glasses increases monotonously with increasing Li2O content, and the glass of 60Li2O-10Nb2O5-30P2O5 shows the value of σ = 2.35 × 10−6 S/cm at room temperature and the activation energy (Ea) of 0.48 eV for Li+ ion mobility in the temperature range of 25-200 °C. It is found that two kinds of the crystalline phases of Li3PO4 and NbPO5 are formed in the crystallization of the glasses and the crystallization results in the decrease in Li+ ion conductivity in all samples, indicating that any high Li+ ion conducting crystalline phases have not been formed in the present glasses. 60Li2O-10Nb2O5-30P2O5 glass shows a bulk nanocrystallization (Li3PO4 nanocrystals with a diameter of ∼70 nm) and the glass-ceramic obtained by a heat treatment at 544 °C for 3 h in air exhibits the values of σ = 1.23 × 10−7 S/cm at room temperature and Ea = 0.49 eV.  相似文献   

8.
Two new cation-deficient hexagonal perovskites Ba4LaMNb3O15 (M = Ti, Sn) ceramics were prepared by high temperature solid-state reaction route. The phase and structure of the ceramics were characterized by X-ray diffraction, scanning electron microscopy (SEM). The microwave dielectric properties of the ceramics were studied using a network analyzer. The Ba4LaTiNb3O15 has high dielectric constant of 52, high quality factors (Q) 3500 (at 4.472 GHz), and temperature variation of resonant frequency (τf) +93 ppm °C−1 at room temperature; Ba4LaSnNb3O15 has dielectric constant of 39 with high Q value of 2510 (at 5.924 GHz), and τf −29 ppm °C−1.  相似文献   

9.
Calcium barium niobate Ca0.28Ba0.72Nb2O6 (CBN-28) crystals were successfully grown by the Czochralski method. X-ray powder diffraction experiments indicated that CBN single crystals are tetragonal with a = 12.432(±0.002) Å and c = 3.957(±0.001) Å, which have almost the same structure as the Sr0.50Ba0.50Nb2O6 (SBN-50) crystal. The thermal expansion coefficient perpendicular to Z-direction had been measured to be 1.25 × 10−5 K−1 between 293.15 and 572.15 K, and along Z-axis was negative between 298.15 and 543.15 K. The specific heat of the crystal had been measured by the differential scanning calorimetric experiments. The transmittance spectra from 200 to 3200 nm were also measured. The measured temperature dependence of dielectric constants showed that the Curie temperature of the CBN-28 crystals is 260 °C, which is about 200 °C higher than that of the (SBN) crystal.  相似文献   

10.
The crystal structure and microwave dielectric properties of the (Sm1−xYx)(Ti1.5W0.5)O6 (x = 0 and 0.5) ceramics sintered at 1375 °C for 2-50 h were investigated in this study. No secondary phase was observed in the samples sintered for various sintering times, whereas a secondary phase was formed in the (Sm0.5Y0.5)(Ti1.5W0.5)O6 ceramic sintered at 1400 °C for 50 h. As for the microstructure analysis, the formation of the liquid phase was observed in the both of the samples sintered for 20 and 50 h. The formation of the liquid phase is related to the compositional change of Ti and W from the stoichiometric composition of the samples caused by the instability of crystal structure. The dielectric constants were increased with increased sintering time in the both of the samples, though variations in the temperature coefficient of resonant frequency of the samples were not recognized with the variation in the sintering time. Moreover, although the quality factors of the each sample increased with increasing the sintering time from 2 to 10 h, decreases in the quality factors were recognized when the sintering time was over 10 h.  相似文献   

11.
The microwave dielectric properties and the microstructures of 0.25 wt.% CuO-doped LaAlO3 ceramics with ZnO additions have been investigated. The sintered LaAlO3 ceramics are characterized by X-ray diffraction spectra and scanning electron microscopy (SEM). Tremendous reduction in sintering temperature can be achieved with the addition of sintering aids CuO and ZnO. The ceramic samples show that dielectric constants (εr) of 22−24 and Q×f values of 33,000−57,000 (at 9.7 GHz) can be obtained at low sintering temperatures 1340−1460°C. The temperature coefficient of resonant frequency varies from −24 to −48 ppm/°C. At the level of 0.25 wt.% CuO and 1 wt.% ZnO additions, LaAlO3 ceramics possesses a dielectric constant (εr) of 23.4, a Q×f value of 57,000 (at 9.7 GHz) and a τf value of −38 ppm/°C at 1400°C for 2 h.  相似文献   

12.
The effects of B2O3 addition, as a sintering agent, on the sintering behavior, microstructure and microwave dielectric properties of the 11Li2O-3Nb2O5-12TiO2 (LNT) ceramics have been investigated. With the low-level doping of B2O3 (≤2 wt.%), the sintering temperature of the LNT ceramic could be effectively reduced to 900 °C. The B2O3-doped LNT ceramics are also composed of Li2TiO3ss and “M-phase” phases. No other phase could be observed in the 0.5-2 wt.% B2O3-doped ceramics sintered at 840-920 °C. The addition of B2O3 induced no obvious degradation in the microwave dielectric properties but increased the τf values. Typically, the 0.5 wt.% B2O3-doped ceramics sintered at 900 °C have better microwave dielectric properties of ?r = 49.2, Q × f = 8839 GHz, τf = 57.6 ppm/°C, which suggest that the ceramics could be applied in multilayer microwave devices requiring low sintering temperatures.  相似文献   

13.
(5 − x)BaO-xMgO-2Nb2O5 (x = 0.5 and 1; 5MBN and 10MBN) microwave ceramics prepared using a reaction-sintering process were investigated. Without any calcinations involved, the mixture of BaCO3, MgO, and Nb2O5 was pressed and sintered directly. MBN ceramics were produced after 2-6 h of sintering at 1350-1500 °C. The formation of (BaMg)5Nb4O15 was a major phase in producing 5MBN ceramics, and the formation of Ba(Mg1/3Nb2/3)O3 was a major phase in producing 10MBN ceramics. As CuO (1 wt%) was added, the sintering temperature dropped by more than 150 °C. We produced 5MBN ceramics with these dielectric properties: ?r = 36.69, Qf = 20,097 GHz, and τf = 61.1 ppm/°C, and 10MBN ceramics with these dielectric properties: ?r = 39.2, Qf = 43,878 GHz, and τf = 37.6 ppm/°C. The reaction-sintering process is a simple and effective method for producing (5 − x)BaO-xMgO-2Nb2O5 ceramics for applications in microwave dielectric resonators.  相似文献   

14.
The system of (1 − y)(Mg0.6Zn0.4)1−xCoxTiO3-yCaTiO3 was investigated to optimize its microwave dielectric properties by adopting appropriate contents of Co and Ca and by controlling sintering conditions. The effect of Co substitution was to enhance densification and Qf value, while the addition of CaTiO3 resulted in increases of dielectric constant and TCF. As an optimal compositions, 0.93(Mg0.6Zn0.4)0.95Co0.05TiO3-0.07CaTiO3 successfully demonstrated a dielectric constant of 23.04, a Qf of 79,460 GHz and a TCF value of +1.4 ppm/°C after firing at a relatively lower sintering temperature of 1200 °C. The increase of sintering temperature beyond 1200 °C tended to degrade overall microwave dielectric properties presumably due to Zn volatilization as evidenced by the presence of a Zn-deficient phase (MgTi2O5) at 1400 °C. An attempt to establish the correlation between microstructure characteristics and dielectric properties was made in this dielectric system where the extensive range of firing temperature up to 1400 °C was evaluated.  相似文献   

15.
(1 − x)Ca2/5Sm2/5TiO3-xLi1/2Nd1/2TiO3 (CSLNT) ceramic powder was prepared by a liquid mixing method using ethylenediaminetetraacetic acid (EDTA) as the chelating agent. TG, DTA, XRD and TEM characterized the precursors and derived oxide powders. When x = 0.3, perovskite CSLNT was synthesized at 1000 °C for 3 h in air. The CSLNT (x = 0.3) ceramics sintered at 1200 °C for 3 h show excellent microwave dielectric properties of ?r = 99, Qf = 6200 GHz and τf = 9 × 10−6 °C−1.  相似文献   

16.
Na0.5Bi0.5Cu3Ti4O12 (NBCTO) ceramics were prepared by conventional solid-state reaction method. The phase structure, microstructure and dielectric properties of NBCTO ceramics sintered at various temperatures with different soaking time were investigated. Pure NBCTO phase could be obtained with increasing the temperature and prolonging the soaking time. High dielectric permittivity (13,495) and low dielectric loss (0.031) could be obtained when the ceramics were sintered at 1000 °C for 7.5 h. The ceramics sintered at 1000 °C for 7.5 h also showed good temperature stability (−4.00 to −0.69%) over a large temperature range from −50 to 150 °C. Complex impedances results revealed that the grain was semiconducting and the grain boundaries was insulating. The grain resistance (Rg) was 12.10 Ω cm and the grain boundary resistance (Rgb) was 2.009 × 105 Ω cm when the ceramics were sintered at 1000 °C for 7.5 h.  相似文献   

17.
In this study, we tried to lower the sintering temperature of Ba0.6Sr0.4TiO3 (BST) ceramics by several kinds of adding methods of Bi2O3, CuO and CuBi2O4 additives. The effects of different adding methods on the microstructures and the dielectric properties of BST ceramics have been studied. In the all additive systems, the single addition of CuBi2O4 was the most effective way for lowering the sintering temperature of BST. When CuBi2O4 of 0.6 mol% was mixed with starting BST powders and sintered at 1100 °C, the derived ceramics demonstrated dense microstructure with a low dielectric constant (? = 4240), low dielectric loss (tan δ = 0.0058), high tunability (Tun = 38.3%) and high Q value (Q = 251). It was noteworthy that the sintering temperature was significantly lowered by 350 °C compared with no-additive system, and the derived ceramics maintained the excellent microwave dielectric properties corresponding to pure BST.  相似文献   

18.
ZnO-(1 − x)TiO2-xSnO2 (x = 0.04-0.2) ceramics were prepared by conventional mixed-oxide method combined with a chemical processing. Fine particle powders were prepared by chemical processing to activate the formation of compound and to improve the sinterability. One wt.% of V2O5 and B2O3 with the mole ratios of 3:1 were used to lower the sintering temperature of ceramics. The effect of Sn content on phase structure and dielectric properties were investigated. The results show that the substituting Sn for Ti accelerates the hexagonal phase transition to cubic phase, and an inverse spinel structure Zn2(Ti1−xSnx)O4 solid solution forms. The best dielectric properties obtained at x = 0.12. The ZnO-0.88TiO2-0.12SnO2 ceramics sintered at 900 °C exhibit a good dielectric property: ?r = 29 and tan δ = 9.86 × 10−5. Due to their good dielectric properties, low firing characteristics, ZnO-(1 − x)TiO2-xSnO2 (x = 0.04-0.2) can serve as the promising microwave dielectric capacitor.  相似文献   

19.
The microwave dielectric properties and the microstructures of Nd(Co1/2Ti1/2)O3 ceramics prepared by conventional solid-state route have been studied. The prepared Nd(Co1/2Ti1/2)O3 exhibited a mixture of Co and Ti showing 1:1 order in the B-site. It is found that low-level doping of B2O3 (up to 0.75 wt.%) can significantly improve the density and dielectric properties of Nd(Co1/2Ti1/2)O3 ceramics. Nd(Co1/2Ti1/2)O3 ceramics with additives could be sintered to a theoretical density higher than 98.5% at 1320 °C. Second phases were not observed at the level of 0.25-0.75 wt.% B2O3 addition. The temperature coefficient of resonant frequency (τf) was not significantly affected, while the dielectric constants (?r) and the unloaded quality factors Q were effectively promoted by B2O3 addition. At 1320 °C/4 h, Nd(Co1/2Ti1/2)O3 ceramics with 0.75 wt.% B2O3 addition possesses a dielectric constant (?r) of 27.2, a Q × f value of 153,000 GHz (at 9 GHz) and a temperature coefficient of resonant frequency (τf) of 0 ppm/°C. The B2O3-doped Nd(Co1/2Ti1/2)O3 ceramics can find applications in microwave devices requiring low sintering temperature.  相似文献   

20.
Using Ca(NO3)2·4H2O, Mg(NO3)2·6H2O, Si(OC2H5)4, LiNO3 and Bi(NO3)3·5H2O as raw materials, CaO-MgO-SiO2 submicron powders were prepared at low temperature by sol-gel method. The crystallization temperature was decreased enormously by the introduction of Li-Bi liquid phase sintering aids into Ca-Mg-Si sol, and the powders with average particle sizes of 80-100 nm and 200-400 nm were obtained at the calcining temperature of 750 °C and 800 °C, respectively. The sintering characteristic and dielectric properties of powders calcined at 750 °C with different content of powders calcined at 800 °C were studied. When the content of powders calcined at 800 °C was 10 wt%, the dielectric ceramic sintered at 890 °C had compact structure, and possessed excellent microwave dielectric properties: ?r = 7.16, Q × f = 25630 GHz, τf = −69.26 ppm/°C.  相似文献   

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