共查询到20条相似文献,搜索用时 15 毫秒
1.
Ping-Shou Cheng Cheng-Fu Yang Ying-Chung Chen Wen-Cheng Tzou 《Ceramics International》2000,26(8):877-881
To establish the correct reaction sequence of BaO–Sm2O3–4TiO2, phases present in different calcining temperatures are identified by X-ray diffraction patterns. When different calcining temperatures are used, the source phase BaO (BaCO3) consumes below 850°C, the source phases TiO2 and Sm2O3 consume at 1000 and 1150°C; the intermediate phases BaTiO3, BaTi4O9, and Sm2Ti2O7 consume at 1050, 1200, and 1250°C, respectively. The BaSm2Ti4O12 phase starts to reveal at the 1100°C-calcined powder. The integrating intensity of BaSm2Ti4O12 phase increases with the raising of calcining temperatures, accompanying with the decrease of integrating intensities of the source and intermediate phases. As the sintering temperature increases, the densities, quality values, and dielectric constants of BaSm2Ti4O12 ceramics increase and saturate at 1325oC. The BaSm2Ti4O12 ceramics sintered at 1325°C have the properties of Q*f=5180,r=81.8, and τf=−19.2 ppm/°C. 相似文献
2.
Preparation, microstructure and microwave dielectric properties of ZrxTi1−xO4 (x=0.40–0.60) ceramics
S. X. Zhang J. B. Li J. Cao H. Z. Zhai B. Zhang 《Journal of the European Ceramic Society》2001,21(16):2931-2936
ZrxTi1−xO4 (x=0.40–0.60) ceramics sintered without additives were prepared from powders made by the coprecipitation of metal salts from aqueous solutions in order to investigate the existence range of a homogeneous phase and the relationships between composition, microstructure and the dielectric properties. XRD, TEM, SEM, EDS, and the dielectric measurements were used to characterize the products. A homogeneous solid solution was obtained. Its crystal structure was isomorphous with ZrTiO4. The variation of the lattice parameters with TiO2 content was discussed. The optimum sintering temperature of samples was dependent of composition. TiO2 suppressed the densification and acted as a grain growth enhancer during the sintering process. With the increase in TiO2 content the relative densities of the sintered bodies decrease, while the grain sizes increase. The dielectric properties at microwave frequency (1.8 GHz) in this system, especially Q value, were poor, due to low densification, impurities and lattice defects. The dielectric constant r and Q value exhibited a significant dependence on the relative density and composition. Both r and Q increased with the increase in relative density, but they were primarily influenced by the composition and the effect of the relative density could be ignored when the relative density was greater than 90% theoretical. r increased slightly with increasing TiO2 content, while Q value decreased. 相似文献
3.
Guillaume Riquet Sylvain Marinel Yohann Breard Christelle Harnois Alain Pautrat 《Ceramics International》2018,44(13):15228-15235
CaCu3Ti4O12 (CCTO) electroceramic possesses unusual giant dielectric permittivity up to ε?=?104 at low frequency range and room temperature. CCTO dielectric properties strongly depend on its microstructure therefore it is essential to pay attention to the processing techniques which impact grain size and microstructure. In this work, direct and hybrid microwave solid state synthesis was specifically designed and used for the synthesis of CCTO. The microwave process was also compared to the conventional process which involves usual infrared heating. The structural (XRD) and microstructural (SEM) characterizations indicate that microwave synthesis is particularly efficient to get rapidly pure CCTO powder. The fully automated 915?MHz single-mode microwave cavity used for hybrid synthesis allows a perfect control of the temperature distribution and heating rate. Therefore hybrid microwave synthesis leads to a fine, mono-disperse and practically pure CCTO powder in the range of 300 – 500?nm. The advantages of the hybrid microwave heating method are discussed and compared to the conventional and direct microwave heating processes. From the powders synthesized by the different routes, dense compacts were sintered in air at 1050?°C in a conventional furnace. Microstructural characterizations reveal abnormal grain growth during sintering which levels dielectric properties. All exhibit a giant dielectric constant ε?>?103 at room temperature which decreases drastically to ε?=?90 at 10?K. Those properties are discussed according to the well-established Internal Barrier Layer Capacitor (IBLC) model. 相似文献
4.
Woo-Joon Lee Jee-Su Kim Nam-Kyoung Kim 《Journal of the European Ceramic Society》2007,27(16):4473-4478
The effects of compositional modification by substituting Mg or Fe for Zn on the perovskite formation, crystallographic aspects, and dielectric properties of Pb(Zn1/2W1/2)O3 were investigated. Microstructural evolutions in the sintered ceramics were also examined. Stabilization of the perovskite structure was accomplished by a much smaller concentration of Mg substitution. Lattice parameters of the perovskite decreased with increasing substituent fractions in general. By contrast, the permittivity values increased significantly with increasing Mg/Fe substitution. 相似文献
5.
In this work, Cu2Ta4O12 ceramic was investigated as a promising, lead-free, nonferroelectric material with high dielectric permittivity. The results of impedance spectroscopy studies carried out at frequencies 10 Hz to 2 MHz over a wide temperature range from −55 to 700 °C were analyzed in the impedance, dielectric permittivity and electric modulus formalisms. In complex impedance plots two distinct arcs were distinguished, ascribed to the semiconducting grains and to the insulating grain boundaries. Cu2Ta4O12 ceramic was found to exhibit a high dielectric permittivity exceeding 10,000 at low frequencies in the temperature range 150–740 °C. High permittivity of this material was attributed to the formation of internal (grain boundary) barrier layer capacitors. The influence of sintering conditions on microstructure, composition and dielectric properties of Cu2Ta4O12 ceramics was also studied. 相似文献
6.
Temperature compensating ZnAl2O4-Co2TiO4 spinel-based low-permittivity microwave dielectric ceramics
TiO2, CaTiO3 and SrTiO3 were added to the 0.79ZnAl2O4-0.21Co2TiO4 (ZACT in abbreviation) system to control its temperature coefficient of resonant frequency (τf). The effects of these additions on sinterability, phase compositions and microwave dielectric properties of the ceramics synthesized by the solid-state reaction were investigated. The results show that TiO2, CaTiO3 and SrTiO3 can all reduce the densification temperature of the ZACT ceramics within the scope from 75 to 150 °C. CoTi2O5 second-phase with negative τf value appears in the TiO2 doped ZACT system, which inhibits TiO2 addition's function for adjusting τf value of ZACT ceramics. While, CaTiO3 and SrTiO3 can both tune effectively τf value to obtain temperature-stable materials. 相似文献
7.
Low sintering temperature ZnNb2O6 microwave ceramics were prepared by doping with mixed oxides of V2O5–Bi2O3 and V2O5–Bi2O3–CuO. The effects of additives on the microstructure and dielectric properties of the ceramics were investigated. The results show that doping with V2O5–Bi2O3 can reduce the sintering temperature of ZnNb2O6 from 1150 °C to 1000 °C due to the formation of V2O5 and Bi2O3 based eutectic phases. The combined influence of V2O5 and Bi2O3 resulted in rod-like grains. Co-doping CuO with 1 wt.% V2O5–1 wt.% Bi2O3 further lowered the sintering temperature to 880 °C, because eutectic phases could be formed between the CuO, V2O5 and Bi2O3. A second phase of (Cu2Zn)Nb2O8 also forms when the content of CuO is greater than 2.5 wt.%. A pure ZnNb2O6 phase can be obtained when the amount of CuO was 1.0–2.5 wt.%. The Q × f values of ZnNb2O6 ceramics doped with V2O5–Bi2O3–CuO were all higher than 25,000 GHz. The dielectric constants were 22.8–23.8 at microwave frequencies. In addition, theτf values decreased towards negative as the content of CuO increased. The ceramic with composition of ZnNb2O6 + 1 wt.%V2O5 + 1 wt.% Bi2O3 + 2.5 wt.% CuO sintered at 880 °C exhibited the optimum microwave dielectric properties, is 23.4, Q × f is 46,975 GHz, and τf is −44.89 ppm/°C, which makes it a promising material for low-temperature co-fired ceramics (LTCCs). 相似文献
8.
Huanfu Zhou Xiaobin LiuXiuli Chen Liang FangYiliang Wang 《Journal of the European Ceramic Society》2012,32(2):261-265
A new low loss spinel microwave dielectric ceramic with composition of ZnLi2/3Ti4/3O4 was synthesized by the conventional solid-state ceramic route. The ceramic can be well densified after sintering above 1075 °C for 2 h in air. X-ray diffraction data show that ZnLi2/3Ti4/3O4 ceramic has a cubic structure [Fd-3m (227)] similar to MgFe2O4 with lattice parameters of a = 8.40172 Å, V = 593.07 Å3, Z = 8 and ρ = 4.43 g/cm3. The best microwave dielectric properties can be obtained in ceramic with relative permittivity of 20.6, Q × f value of 106,700 GHz and τf value of −48 ppm/°C. The addition of BaCu(B2O5) (BCB) can effectively lower the sintering temperature from 1075 °C to 900 °C and does not induce much degradation of the microwave dielectric properties. Compatibility with Ag electrode indicates that the BCB added ZnLi2/3Ti4/3O4 ceramics are good candidates for LTCC applications. 相似文献
9.
10.
The microwave dielectric properties of Sm(Mg0.5Ti0.5)O3 incorporated with various amount of Bi2O3 and B2O3 additives have been investigated systematically. In this study, both Bi2O3 and B2O3 additives acting as a sintering aid can effectively lower the sintering temperature from 1550 °C to 1300 °C. The ionic radius of Bi3+ for a coordination number of 6 is 0.103 nm, whereas the ionic radius of B3+ is 0.027 nm. Clearly, the ionic radius of Bi3+ is greatly larger than one of B3+, which resulted in the specimens incorporated with Bi2O3 having larger lattice parameters and cell volume than those incorporated with B2O3. The experimental results show that no second phase was observed throughout the entire experiments. Depending on the interfacial tension, the liquid phase may penetrate the grain boundaries completely, in which case the grains will be separated from one another by a thin layer as shown in Sm(Mg0.5Ti0.5)O3 ceramics incorporated with Bi2O3. Whereas, in Sm(Mg0.5Ti0.5)O3 ceramics incorporated with B2O3, the volume fraction of liquid is high, the grains may dissolve into the liquid phase, and rapidly rearrange, in which case contact points between agglomerates will be dissolved due to their higher solubility in the liquid, leading plate-like shape microstructure.A dielectric constant (?r) of 29.3, a high Q × f value of 26,335 GHz (at 8.84 GHz), and a τf of −32.5 ppm/°C can be obtained for Sm(Mg0.5Ti0.5)O3 ceramics incorporated with 10 mol% Bi2O3 sintered at 1300 °C. While Sm(Mg0.5Ti0.5)O3 ceramics incorporated with 5 mol% B2O3 can effectively lower temperature coefficient of resonant frequency, which value is −21.6 ppm/°C. The Sm(Mg0.5Ti0.5)O3 ceramic incorporated with heavily Bi2O3 and B2O3 additives exhibits a substantial reduction in temperature (∼250 °C) and compatible dielectric properties in comparison with that of an un-doped one. This implied that this ceramic is suitable for miniaturization in the application of dielectric resonators and filters by being appropriately incorporated with a sintering aid. 相似文献
11.
Dy substituted CCTO ceramics were synthesized using solid state reaction method. Effect of Dy on structural, microstructural, dielectric and electrical properties has been studied over a wide temperature (300–500 K) and frequency range (100 Hz–1 MHz). Rietveld refinement, carried out on the samples, confirmed single phase formation and indicated overall decrease in lattice constant. Microstructure showed bimodal distribution of grains in CCTO with bigger grains surrounded by smaller grains. Dy substitution reduced grain size. Dy substitution in CCTO reduces the dielectric constant which may be attributed to increase of the Schottky potential barrier. The dielectric constant remains nearly constant in temperature range 300–400 K. The AC conductivity obeys a power law, σac=A fn, where n is the temperature dependent frequency exponent. The AC conductivity behaviour can be divided into three regions, over entire temperature range, depending on conduction processes. The relevant charge transport mechanisms have been discussed. 相似文献
12.
Microwave dielectric properties of Ba3Ti4−x(Zn1/3Nb2/3)xNb4O21 for low temperature co-fired ceramics
The effects of substitution of (Zn1/3Nb2/3) for Ti on the sintering behavior and microwave dielectric properties of Ba3Ti4−x(Zn1/3Nb2/3)xNb4O21 (0 ≤ x ≤ 4) ceramics have been investigated. The dielectric constant (?r) and the temperature coefficient of the resonant frequency (τf) of Ba3Ti4−x(Zn1/3Nb2/3)xNb4O21 ceramics decreased with increasing x. However, the Q × f values enhanced with the substitution of (Zn1/3Nb2/3) for Ti. It was found that a small amount of MnCO3-CuO (MC) and ZnO-B2O3-SiO2 (ZBS) glass additives to Ba3Ti4−x(Zn1/3Nb2/3)xNb4O21 (x = 2) ceramics lowered the sintering temperature from 1250 to 900 °C. And Ba3Ti4−x(Zn1/3Nb2/3)xNb4O21 (x = 2) ceramics with 1 wt% MC and 1 wt% ZBS sintered at 900 °C for 2 h showed excellent dielectric properties: ?r = 53, Q × f = 14,600 GHz, τf = 6 ppm/°C. Moreover, it has a chemical compatibility with silver, which made it as a promising material for low temperature co-fired ceramics technology application. 相似文献
13.
Xiaochi Lu Wenjie Bian Chengfa Min Zhenxiao Fu Qitu Zhang Haikui Zhu 《Ceramics International》2018,44(9):10028-10034
In current study, only 5?mol% Mn2+ was applied to fabricate high performance microwave dielectric ZnGa2O4 ceramics, via a traditional solid state method. The crystal structure, cation distribution and microwave dielectric properties of as-fabricated Mn-substituted ZnGa2O4 ceramics were systematically investigated. Mn2+-substitution led to a continuous lattice expansion. Raman, EPR and crystal structure refinement analysis suggest that Mn2+ preferentially occupies the tetrahedral site and the compounds stay normal-spinel structure. The experimental and theoretical dielectric constant of Zn1-xMnxGa2O4 ceramics fit well. In all, this magnetic ion, Mn2+, could effectively adjust the τf value to near zero and double the quality factor from 85,824?GHz to 181,000?GHz of Zn1-xMnxGa2O4 ceramics at the meantime. Zn1-xMnxGa2O4 (x?=?0.05) ceramics sintered at 1400?°C for 2?h exhibited excellent microwave dielectric properties, with εr =?9.7(@9.85?GHz), Q?×?f?=?181,000?GHz, tanδ?=?5.44?×?10?5,and τf =???12?ppm/°C. 相似文献
14.
Ba4Nd9.33Ti18O54·x wt%Al2O3 (BNT-A) ceramics (x=0, 0.5, 1.0, 1.5, 2.0, 2.5) were prepared by the conventional solid state reaction. The effects of Al2O3 on the microstructure and microwave dielectric properties of Ba4Nd9.33Ti18O54 (BNT) ceramics were investigated. X-ray diffraction and backscatter electronic images showed that the Al2O3 additive gave rise to a second phase BaAl2Ti5O14 (BAT). The formation mechanism and grain growth of the BAT phase were first discussed. Dielectric property test revealed that the Al2O3 additive had improved the dielectric properties of the BNT ceramics: increased the Q×f value from 8270 to 12,180 GHz and decreased the τf value from 53.4 to 11.2 ppm/°C. A BNT-A ceramic with excellent dielectric properties: εr=70.2, Q×f=12,180 GHz, τf=20 ppm/°C was obtained with 2.0 wt% Al2O3 added after sintering at 1320 °C for 4 h. 相似文献
15.
Yong Chen Can-Can Zhang Lu Qin Chao-Bin Jiang Kang-Hui Liu Chao Ma Zhen-Tao Wu Rui-Kun Pan Wan-Qiang Cao Cong Ye Zhang Li 《Ceramics International》2018,44(15):18264-18270
The bismuth layer-structured Na0.5Bi4.5-xPrxTi4O15 (x?=?0, 0.1, 0.2, 0.3, 0.4, and 0.5) (NBT-xPr3+) ceramics were fabricated using the traditional solid reaction process. The effect of different Pr3+ contents on dielectric, ferroelectric and piezoelectric properties of Na0.5Bi4.5Ti4O15 ceramics were investigated. The grain size of Pr3+-doping ceramics was found to be smaller than that of pure one, the maximum dielectric constant and Curie temperature Tc gradually decreased with increasing Pr3+ contents, and the dielectric loss decreased at high temperature by Pr3+-doping. Moreover, the activation energy (Ea), resistivity (Z’), remanent polarization (2Pr) and piezoelectric constant (d33) increased by Pr3+-doping. The NBT-xPr3+ ceramics with x?=?0.3 achieved the optimal properties with the maximum dielectric constant of 1109.18, minimum loss of 0.00822 (250?kHz), Ea of 1.122?eV, Z’ of 7.9?kΩ?cm (725 ºC), d33 of 18 pC/N, 2Pr of 12.04 μC/cm2. The enhancement was due to the addition of Pr3+ which suppressed the decreasing of resistivity at high temperature and made it possible for NBT-xPr3+ ceramics to be poled in perpendicular direction, implying that it is a great improvement for Na0.5Bi4.5Ti4O15 ceramics in electrical properties. 相似文献
16.
Recently, the rapid development of advanced communication systems increasingly strongly demands high-performance microwave dielectric ceramics in microwave circuits. Among them, Li2ZnTi3O8 ceramics have been one of the most widely investigated species, due to its high quality factor, moderate firing conditions and low cost. However, the dielectric constants of the already reported Li2ZnTi3O8 ceramics are fixed in a narrow range, limiting their wider applications. To adjust the dielectric constant of the Li2ZnTi3O8 based ceramics, in this work Li2ZnTi3O8 ceramics added with different amounts of Al2O3 (0–8?wt%) were prepared by conventional solid-state reaction. The microstructure and microwave dielectric properties of the samples were investigated. Due to the addition of Al2O3, the sintering temperature of the ceramics would be increased somewhat. Some Al3+ ions could substitute for Ti4+ ions in Li2ZnTi3O8, and the added Al2O3 would react with ZnO to produce a ZnAl2O4 phase accompanying with the formation of TiO2 phase, which would inhibit the growth of Li2ZnTi3O8 grains. The dielectric constant of the finally obtained ceramics would be reduced from 26.2 to 17.9, although the quality factors of the obtained ceramics would decrease somewhat and the temperature coefficient of resonant frequency would deviate further from zero. 相似文献
17.
Wei Zhou Rui-ming Yin Lan Long Heng Luo Wei-da Hu Yan-hong Ding Yang Li 《Ceramics International》2018,44(11):12301-12307
Si3N4 ceramics modified with SiC nanofibers were prepared by gel casting aiming to enhance the dielectric and microwave absorption properties at temperatures ranging from 25?°C to 800?°C within X-band (8.2–12.4?GHz). The results indicate that the complex permittivity and dielectric loss are significantly increased with increased weight fraction of SiC nanofibers in the Si3N4 ceramics. Meanwhile, both complex permittivity and dielectric loss of SiC nanofibers modified Si3N4 ceramics are obviously temperature-dependent, and increase with the higher test temperatures. Increased charges mobility along conducting paths made of self-interconnected SiC nanofibers together with multi-scale net-shaped structure composed of SiC nanofibers, Si3N4 grains and micro-pores are the main reason for these enhancements in dielectric properties. Moreover, the calculated microwave absorption demonstrates that much enhanced microwave attenuation abilities can be achieved in the SiC nanofibers modified Si3N4 ceramics, and temperature has positive effects on the microwave absorption performance. The SiC nanofibers modified Si3N4 ceramics will be promising candidates as microwave absorbing materials for high-temperature applications. 相似文献
18.
Dong-Xiang Zhou Rong-Guang Sun Shu-Ping Gong Yun-Xiang Hu 《Ceramics International》2011,37(7):2377-2382
A potential low temperature co-fired ceramics system based on zinc borate 3ZnO–2B2O3 (3Z2B) glass matrix and Al2O3 filler was investigated with regard to phase development and microwave dielectric properties as functions of the glass content and sintering temperature. The densification mechanism for 3Z2B–Al2O3 composites was reported. The linear shrinkage of 3Z2B glass–Al2O3 composites exhibited a typical one-stage densification behavior. XRD patterns showed that a new crystalline phase, ZnAl2O4 spinel, formed during densification, indicating that certain chemical reaction took place between the 3Z2B glass matrix and the alumina filler. Meanwhile, several zinc borate phases, including 4ZnO·3B2O3, crystallized from the glass matrix. Both of the reaction product phase and crystallization phases played an important role in improving the microwave dielectric properties of composites. The optimal composition sintered at 850–950 °C showed excellent microwave dielectric properties: ?r = ∼5.0, Q·f0 = ∼8000 GHz, and τf = ∼−32 ppm/°C at ∼7.0 GHz. 相似文献
19.
Ce2(WO4)3 ceramics have been synthesized by the conventional solid-state ceramic route. Ce2(WO4)3 ceramics sintered at 1000 °C exhibited ?r = 12.4, Qxf = 10,500 GHz (at 4.8 GHz) and τf = −39 ppm/°C. The effects of B2O3, ZnO–B2O3, BaO–B2O3–SiO2, ZnO–B2O3–SiO2 and PbO–B2O3–SiO2 glasses on the sintering temperature and microwave dielectric properties of Ce2(WO4)3 were investigated. The Ce2(WO4)3 + 0.2 wt% ZBS sintered at 900 °C/4 h has ?r = 13.7, Qxf = 20,200 GHz and τf = −25 ppm/°C. 相似文献
20.
Sea-Fue Wang Yung-Fu Hsu Yuh-Ruey Wang Yong-Han Huang 《Journal of the European Ceramic Society》2011,31(15):2975-2980
In this study, densification, microstructural evolution and microwave dielectric properties of (1 − x)BiSbO4–xBi2Mo2O9 ceramics (x = 0–0.25) were investigated. Bi2Mo2O9 was selected as the sintering aid as well as the modifier of the dielectric properties for BiSbO4 ceramic. In comparison with pure BiSbO4 densified at 1100 °C, the 0.75BiSbO4–0.25Bi2Mo2O9 composites emerged to reach maximum sintering density at 775 °C. No other second phase was detected while the microstructure exhibited a bimodal grain size distribution as both 1–2 μm large grains of Bi2Mo2O9 and 0.2–0.5 μm fine grains of BiSbO4 were observed. The ceramic with the best performance in terms of microwave dielectric properties in this system is found to be the 0.82BiSbO4–0.18Bi2Mo2O9 composite, which reports a ?r of 24.3, a Q × f of 24,019 GHz, and a τf of −4 ppm/°C when sintered at 825 °C. 相似文献