Kamini Kumari
材料科学技术（英）
Structural and dielectric properties of polycrystalline samples of lead-free (1-x)(Na1/2Bi1/2)TiO3-xZnO, prepared using a high-temperature solid-state reaction method, are investigated in the composition range 0 ≤ x ≤ 0.10. Rietveld analyses of X-ray diffraction data indicated the formation of a single-phase hexagonal structure with R3c symmetry. Williamson-Hall approach was applied to estimate the apparent particle size and lattice strain of the compounds. Temperature dependence of dielectric constant showed that the addition of ZnO to (Na1/2Bi1/2)TiO3 shifts the phase transition temperature towards higher side, a property favourable for practical applications of these ceramics. Further, temperature dependent permittivity data provided low temperature coefficient of capacitance (TCC < 8%) up to 100°C. Furthermore, a decrease in the value of dielectric loss with an increase in ZnO content is observed.
关键词:
Lead-free
Shunhua WU
,
Guoqing WANG
,
Shuang WANG
,
D
,
an LIU
材料科学技术（英）
The effect of Sn4+ (BaSnO3) B-site substitution on the microstructure and dielectric properties of Ba(Mg1/3Ta2/3O3 microwave ceramics was investigated. X-ray diffraction shows that a complex perovskite material Ba(Mg1/3Ta2/3)O3 was prepared. As Sn4+ content x increases in the (1-x) Ba(Mg1/3Ta2/3)O3-xBaSnO3 (x=0.00～0.20) system, the dielectric constant generally keeps unchanged, while TCF changes from positive to negative. Although the addition of Sn4+ reduces the ordering degree, Qf0 is still increased when the ceramics density increases. This trend implies that Qf0 of this system is mostly determined by ceramics density rather than ordering degree. After sintering at 1500℃ for 3 h, the system with x=0.15 was found to have excellent dielectric properties as follows: ε≈25, Qf0≥300,000 GHz at 7 GHz, TCF=-0.6×10-6℃.
关键词:
Ba(Mg1/3Ta2/3)O3
,
null
,
null
,
null
Kamini Kumari
材料科学技术（英）
Structural and dielectric properties of polycrystalline samples of lead-free (1-x)(Na1/2Bi1/2)TiO3-xZnO, prepared using a high-temperature solid-state reaction method, are investigated in the composition range 0 ≤ x ≤ 0.10. Rietveld analyses of X-ray diffraction data indicated the formation of a single-phase hexagonal structure with R3c symmetry. Williamson-Hall approach was applied to estimate the apparent particle size and lattice strain of the compounds. Temperature dependence of dielectric constant showed that the addition of ZnO to (Na1/2Bi1/2)TiO3 shifts the phase transition temperature towards higher side, a property favourable for practical applications of these ceramics. Further, temperature dependent permittivity data provided low temperature coefficient of capacitance (TCC < 8%) up to 100°C. Furthermore, a decrease in the value of dielectric loss with an increase in ZnO content is observed.
关键词:
Lead-free
JunhHua WU
材料科学技术（英）
Microwave dielectric measurements over the broad bandwith of 10 MHz to 20 GHz were conducted on composites comprising bundles of single-walled carbon nanotubes (SWNT) embedded in an epoxy matrix, in comparison to the nano-graphite and MWNT. It is found that both relative real and imaginary permittivity of the nanocomposites are strong functions of the SWNT concentration, showing large, wide dielectric and electrical response. Distinct resonance around 1.5 GHz is observed at high SWNT concentrations, accompanied by the downshift of the resonance frequency with increasing concentration. Largely, the SWNT-epoxy composites share the behavior of the MWNT owing to structural similarity, much more effective than the nano-graphite. The remarkable, broadband dielectric and electrical properties of the nanotubes acquired in the work originate from their unique seamless graphene architectures, modeled by two major contributions, dielectric relaxation/resonance and electronic conduction, which is substantiated by the agreement between theoretical analysis and experimental results. The carbon nanotube composites are prospective for microwave applications and offer experimental evidence for fundamental studies in low-dimensional systems.
关键词:
Single-walled carbon nanotube
,
carbon
,
nanotube
,
Dielectric
张丽娟
,
王洋
,
李文静
,
金兆国
,
刘斌
宇航材料工艺
doi:10.3969/j.issn.1007-2330.2015.04.011
针对高马赫数飞行器中恶劣热环境对透波隔热材料的需求,采用溶胶-凝胶方法,以透波型石英纤维为增强体,通过超临界干燥及后处理制备透波二氧化硅气凝胶复合材料;并采用扫描电子显微镜、平板导热仪、石英灯辐射加热及万能电子试验机等手段对材料的微观形貌结构、隔热性能、耐温性及力学性能进行了表征.结果表明:二氧化硅透波气凝胶复合材料有良好的介电性能,介电常数在1.28 ～1.39可调、损耗角正切≤0.005;耐温性≥1 100℃、室温热导率≤0.02 W/(m·K);具有较好的力学性能,能保证飞行器在恶劣飞行环境中的通讯、遥测、制导等系统的正常工作.
关键词:
耐高温
,
透波
,
气凝胶
,
介电性能
白婧婧
,
乌江
,
王金锋
,
郑晓泉
,
李盛涛
宇航材料工艺
doi:10.3969/j.issn.1007-2330.2010.01.014
采用非线性添加剂对聚酰亚胺进行电导率改性,研究了改性前后介质的电导特性及其他介电性能,以及添加剂含量对聚酰亚胺复合介质材料电导特性的影响.结果表明,改性后的复合试样的体电导率随添加剂质量分数的变化而变化,当质量分数小于5%时,电导率略有下降,大于5%时显著上升.改性后的复合介质材料的非线性电导率特性变化显著.
关键词:
聚酰亚胺
,
改性
,
非线性电导
,
介电性能
