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1.
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   

2.
Ag-doped BaTiO3 based X7R (temperature coefficient of capacitance within the range of ±15% between −55 and +125 °C) ceramics with different amounts of silver (0.0-20.0 mol%) were prepared in this paper. The X-ray diffraction analysis indicated that no phases other than BaTiO3 and silver were observed in the ceramics. The energy dispersive X-ray spectroscopy analysis showed that the silver particles presented homogeneous distribution in the BaTiO3 ceramics. The dielectric properties of Ag-doped ceramics were investigated. A small amount of silver (<0.5 mol%) and a large amount of silver (>2.0 mol%) could both improve the sintered density and permittivity, but more content of silver (0.5-2.0 mol%) would decrease the relative density and permittivity. Specially, the temperature coefficient of capacitors of the ceramics doped with 20 mol% silver still met the X7R characteristics, and the room temperature permittivity of the ceramics was 6823, which was the highest dielectric constant in the BaTiO3 based X7R ceramics.  相似文献   

3.
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   

4.
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   

5.
Non-aqueous gelcasting and dry pressing were used to prepare 45 wt% Ba0.6Sr0.4TiO3-55 wt% MgO (BSTM) ceramics. The effects of different forming methods on the microstructures and dielectric properties of the BSTM ceramics were investigated. The densities of the BSTM ceramics prepared by non-aqueous gelcasting are lower but more uniform than that of the BSTM ceramics prepared by dry pressing. The XRD analysis illustrates that phase compositions are completely the same no matter what forming method is adopted. The SEM results show that the BSTM green samples and sintered ceramics prepared by non-aqueous gelcasting are more uniform than that prepared by dry pressing. Furthermore, it is found that the BSTM ceramics prepared by non-aqueous gelcasting have higher and more uniform dielectric constant, tunability and loss tangent (measured at 10 kHz and 20 °C). Meanwhile, the BSTM ceramics prepared by non-aqueous gelcasting have higher dielectric constant and lower Q × f value (namely more loss) when they are measured at microwave frequencies.  相似文献   

6.
The CuO and SnO2 co-modified Na0.52K0.48NbO3 ceramics were prepared by a conventional mixed oxide method. Densification can be further improved but the grain growth is inhibited as a small amount of SnO2 is added into 1% CuO doped Na0.52K0.48NbO3. The results indicate that the physical and various electrical properties of CuO and SnO2 doped Na0.52K0.48NbO3 ceramics significantly depend on sintering conditions and the content of dopants. The ceramics doped with 1 mol% CuO and 1 mol% SnO2 sintered at 1070 °C for 3 h show improved dielectric and piezoelectric properties: d33 = 120 pC/N, kp = 0.38, Qm = 1040, ?r = 710 and tanδ = 0.013 (1 kHz), in comparison with un-doped or CuO doped compositions.  相似文献   

7.
Dense BiFeO3 ceramics were prepared by a novel spark plasma sintering (SPS) technique. The sintering was conducted at temperatures ranging from 675 to 750 °C under 70 MPa pressure. A bulk density value up to 96% of theoretical density was achieved in the process. This contrast to around 90% of the theoretical density achieved by conventional sintering at around 830 °C. It was found that the tendency to form unwanted Bi2Fe4O9 phase is higher at a high sintering temperature for SPS. The dielectric and ferroelectric properties also improved (with respect to conventionally sintered sample) for spark plasma-sintered samples.  相似文献   

8.
Cordierite-based ceramics were developed by sintering a glass selected from MgO-Al2O3-SiO2 system with an aim to use the material as high frequency chip inductors. A small amount of B2O3 and P2O5 were added to optimize the preparation conditions. The glass powder and sintered bodies were characterized by different analytical techniques such as TG-DTA analysis, X-ray diffraction, transmission and scanning electron microscopy. Pellets uniaxially pressed from the glass power could be sintered well at 950 °C having a density of above 99% theoretically, dielectric constant of 5.5, dielectric loss of 0.001 and thermal expansion coefficient of 26.7×10−7 °C−1 (20-400 °C). Crystalline phases in this sintered sample are predominantly α-cordierite (hexagonal high cordierite) and trace amount of μ-cordierite. SEM depicted a uniformly dense microstructure with crystals of granular habit in the sintered sample.  相似文献   

9.
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   

10.
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   

11.
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   

12.
We demonstrate the correlation between sintering behavior and microstructural observations in low-temperature sintered, LaNbO4 microwave ceramics. Small CuO additions to LaNbO4 significantly lowered the sintering temperature from 1250 to 950 °C. To elucidate the sintering mechanism, the internal microstructure of the sample manipulated by a focused ion beam (FIB) was investigated using transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS). LaNbO4 with 3 wt% CuO sintered at 950 °C for 2 h possessed the following excellent microwave dielectric properties: a quality factor (Qxf) of 49,000 GHz, relative dielectric constant (?r) of 19.5, and temperature coefficient of resonant frequency (τf) of 1 ppm/°C. The ferroelastic phase transformation was also investigated using in situ X-ray diffraction (XRD) to explain the variation of τf in low-temperature sintered LaNbO4 as a function of CuO content.  相似文献   

13.
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   

14.
(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   

15.
The addition of a small amount of CuO to the 0.95(Na0.5K0.5)NbO3-0.05CaTiO3 (0.95NKN-0.05CT) ceramics sintered at 960 °C for 10 h produced a dense microstructure with large grains due to the liquid phase sintering. Due to the negligible Na2O evaporation, poling was easy for all specimens sintered at 960 °C. The piezoelectric properties of the specimens were considerably influenced by the relative density, grain size and liquid phase amount. The high piezoelectric properties of d33 = 200 pC/N, kp = 0.37, and Qm = 350 were obtained for the 0.95NKN-0.05CT ceramics containing 2.0 mol% CuO sintered at 960 °C for 10 h. Therefore, the 0.95NKN-0.05CT ceramics containing a small amount of CuO are a good candidate material for lead-free piezoelectric ceramics.  相似文献   

16.
The microwave characteristics and the microstructures of 0.88Al2O3-0.12TiO2 with various amounts of MgO-CaO-SiO2-Al2O3 (MCAS) glass sintered at different temperatures have been investigated. The sintering temperature can be lowered to 1300 °C by the addition of MCAS glass. The densities, dielectric constants (εr) and quality values (Q×f) of the MCAS-added 0.88Al2O3-0.12TiO2 ceramics decrease with the increase of MCAS glass content. The temperature coefficients of the resonant frequency (τf) are shifted to more negative values as the MCAS content or the sintering temperatures increase. The change of the crystalline phases of Al2TiO5 phase and rutile-TiO2 phase has profound effects on the microwave dielectric properties of the MCAS-added Al2O3-TiO2 ceramics. As sintered at 1250 °C, 0.88Al2O3-0.12TiO2 ceramics with 2 wt.% MCAS glass addition exists a εr value of 8.63, a Q×f value of 9578 and a τf value of +5 ppm/°C.  相似文献   

17.
Ba8Zn(Nb6−xSbx)O24 (x = 0, 0.3, 0.6, 0.9, 1.2, 1.5, 1.8 and 2.4) ceramics were prepared through the conventional solid-state route. The materials were calcined at 1250 °C and sintered in the range 1400-1425 °C. The structure of the system was analyzed by X-ray diffraction, Fourier transform infrared and Raman spectroscopic methods. The theoretical and experimental densities were calculated. The microstructure of the sintered pellets was analyzed using scanning electron microscopy. The low frequency dielectric properties were studied in the frequency range 50 Hz-2 MHz. The dielectric constant (?r), temperature coefficient of resonant frequency (τf) and the unloaded quality factor (Qu) are measured in the microwave frequency region using cavity resonator method. The τf values of the samples reduced considerably with the increase in Sb concentration. The materials have intense emission lines in the visible region. The compositions have good microwave dielectric properties and photoluminescence and hence are suitable for dielectric resonator and ceramic laser applications.  相似文献   

18.
Si3N4-TiN composites were prepared by spark plasma sintering (conventional sintering (SPS1) and in situ reaction sintering (SPS2)). Homogeneous distribution of equiaxed TiN grains in Si3N4 matrix results in the highest microhardness (21.7 GPa) and bending strength (621 MPa) of sample SPS1 sintered at 1550 °C. Dispersion of elongated TiN grains in Si3N4 matrix results in the highest fracture toughness (8.39 MPa m1/2) of sample SPS2 sintered at 1300 °C.  相似文献   

19.
Phase composition, microstructure and tunable dielectric properties of (1 − x)BaZr0.25Ti0.75O3-xMgO (BZTM) composite ceramics fabricated by solid-state reaction were investigated. It was found Mg not only existed in the matrix as MgO, there was also trace amount of Mg2+ ions dissolved in the BZT grains, which led to Curie temperature of the BZTM composites ceramics shifting to below −100 °C. Dielectric permittivity of the BZTM composite ceramics was reduced from thousands to hundreds by manipulating the content of MgO. Johnson's phenomenological equation based on Devonshire's theory was used to describe the nonlinear dielectric permittivity of the ceramics with increasing applied DC field. With increasing content of MgO, anharmonic constant α(T) increased monotonously. Dielectric permittivity was 672, while dielectric tunability was as high as 30.0% at 30 kV/cm and dielectric loss was around 0.0016 for the 0.6BaZr0.25Ti0.75O3-0.4MgO sample at 10 kHz and room temperature.  相似文献   

20.
Rare earth and alkaline earth co-doped Ce0.85La0.10Ca0.05O2−δ electrolyte material with the powder obtained by solid-state reaction method was sintered at 1300, 1400, 1500 and 1600 °C respectively. The results showed that the ionic conductivity of the sample sintered at 1400 °C was slightly lower compared to that sintered at 1500 °C in the temperature range of 300-550 °C, while the sample sintered at 1400 °C showed the highest ionic conductivity in all the samples above 550 °C. The ionic conductivity of ∼0.021 S/cm at 600 °C and the relative density of 98.2% were observed for the sample sintered at 1400 °C. In addition, the highest flexural strength with 145 MPa was also obtained for the sample sintered at 1400 °C. It suggested that the sintering temperature for Ce0.85La0.10Ca0.05O2−δ electrolyte may be reduced to as low as 1400 °C with desired properties.  相似文献   

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