Papers by Keyword: Dielectric Ceramics

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Authors: Alexander Tkach, Branca Araújo, Paula M. Vilarinho
Abstract: The effect of the electric field on the dielectric response of the Sr1-xCaxTiO3 ceramic system was analysed and complemented by structural and microstructural studies. A monotonic decrease of the lattice parameter and an increase of the average grain size from 11 to 23 μm with increasing x were observed by X-ray diffraction and scanning electron microscopy analysis respectively. Samples with x = 0.003 and 0.01 reveal a monotonous increase of low-temperature dielectric constant, corresponding to an enhancement of the tunability and a reduction of the driving electric field at 10-30 K for x = 0.01. For Sr1-xCaxTiO3 ceramic samples with x = 0.04 and 0.10 the ferroelectric phase transition of around 20 K was observed together with the enhanced tunability of the dielectric constant at 30-85 K for x = 0.10.
240
Authors: Xi Geng Miao, Jing Jing Liu, Fabrizia Ghezzo, Xiao Wei Fang, Zhi Ya Zhao, Ruo Peng Liu
Abstract: Microwave filters require dielectric ceramic resonators attached to ceramic supports via joining. Among the BaTiO3, CaTiO3, and Ba2Ti9O20 based-dielectric ceramics prepared in our labs., the CaTiO3 ceramics modified with NdAlO3 and Al2O3 gave satisfactory dielectric properties: dielectric constant DK = 40.69, quality factor Qxf = 18842 GHz (fo = 6.551 GHz), and frequency temperature coefficient tf = 2.542 ppm °C-1. For replacing the hard-to-sinter Al2O3 based-ceramic supports, a glass-ceramic of the SiO2-B2O3-P2O5-ZnO system was developed, leading to a low sintering temperature of 900 °C, and a low dielectric constant (<4). Finally, a Bi2O3-ZnO-SiO2-Al2O3-CaO glass was used as a sealing agent to replace the traditional gluing consisting of an adhesive. The present work hinters that with proper sintering aids, one can produce multilayered and integrated resonators with and without embedded passive elements.
294
Authors: Uilame Umbelino Gomes, Wilson Acchar, E.C.S. Tavares, N.F. Silva
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Authors: Ion Teoreanu, A. Folea, Adrian Volceanov
1203
Authors: Fei Shi, Peng Cheng Du, Jing Xiao Liu, Ji Wei Wu, De Qing Chen, Xiao Li Dong, Hong Chao Ma
Abstract: The Mg2SiO4-MgTiO3-CaTiO3 composite dielectric ceramics with different Mg2SiO4 addition amounts were prepared by solid state reaction method. The effects of Mg2SiO4 addition amounts on the microstructure and dielectric properties as well as sintering temperature of xMg2SiO4-(0.95-x)MgTiO3-0.05CaTiO3 (abbreviated as xMSTC, 0.25≦x≦0.75) composite ceramics were investigated. The results indicated that the sintering temperature of MgTiO3-CaTiO3 based ceramics with Mg2SiO4 addition could be lowered effectively to 1320~1340°C, and the dielectric constant decreased and dielectric loss increased gradually with the increase of Mg2SiO4 content. The 0.45MSTC ceramics containing 45 wt% Mg2SiO4 and sintered at 1340°C showed desirable dielectric properties with dielectric constant εr=13.3,dielectric loss tanδ=4.5×10-4 and temperature coefficient of relative permittivity τε =10 ppm/°C.
200
Authors: Jing Pei, Zhen Xing Yue, Fei Zhao, Zhi Lun Gui, Long Tu Li
Abstract: The nano-sized Ba(Zr0.2Ti0.8)O3 powder was prepared by citrate sol-gel method. The crystal structure and the particle size of the powder were characterized by XRD. The morphology of calcined powder and the sintered ceramics was observed by TEM and SEM, respectively. The particle size of the powders calcined at 600oC is about 10 nm. The dense ceramics can be obtained at sintering temperature of 1220 oC, which is much lower than that of the powder prepared by the conventional solid method. The effects of Al2O3 additive on the sintering behavior, microstructure and dielectric properties of Ba(Zr0.2Ti0.8)O3 ceramics were also investigated.
76
Authors: Alexander Tkach, Paula M. Vilarinho, Andréi L. Kholkin, Ian M. Reaney, Jan Petzelt
40
Authors: Hai Tang Hua, Xin You Huang, Zhi Wen Zhu, Yin Qun Hua, Yan Li
Abstract: (Bi2-xLix) (Mg2/3Nb1.1833Sn0.15)O7 piezoelectric ceramics were prepared by conventional solid state reaction method. The microstructure and dielectric properties of dielectric ceramics were studied which was doped by different amount of Li2CO3. The experiment results showed that the density of the ceramics would decrease, but have little effect on the microstructure of the ceramics when the amount of the Li2CO3 doped increases. With the increasing of Li2CO3 doped, the dielectric constant(εr) and dielectric loss(tanδ) of dielectric ceramics first decreases and then increases. When tested in 1MHz frequency, the piezoelectric ceramics display the optimum properties tanδ is 0.00009, εr is 163 while Li2CO3 doped amount is 0.05 mol%.
749
Authors: Chun Yuan Luo, Jing Xiao Liu, Fei Shi, Ji Wei Wu, Chao Qian, Peng Cheng Du
Abstract: AST-doped ZnO-MgTiO3-SrTiO3 ceramics were prepared using a solid-state sintering process. The effects of AST (Al2O3-SiO2-TiO2) on the dielectric properties of MgTiO3-based ceramics were investigated. The results indicate that AST-doped MgTiO3-based ceramics could be obtained after 1205~1280°C sintering for 3 h. The XRD results indicate that the obtained MgTiO3-based ceramics contain high percentage of MgTi2O5 phase and the percentage increased with the increase of AST content. It was found that the occurred liquid-phase sintering by adding AST glass could effectively lower the sintering temperature and decrease the dielectric loss of MgTiO3-based ceramics. A minimum tanδ of 1.5×10-4 associated with εr=19.0 was achieved for 6.0 wt% AST-doped samples sintered at 1255°C.
2378
Authors: F. Xiao, R. Chen, Zhi Hong Huang, Zhao Xian Xiong
Abstract: Two measuring techniques, the parallel plate method and the cylinder cavity perturbation method, for complex permittivity of microwave dielectric ceramics were introduced. Attention was focused on the theoretical consideration of measurement precision and suitable applications of the techniques.
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