High-Performance Ceramics III

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Authors: Zong Hui Zhou, Pi Yi Du, Gao Rong Han, Wen Jian Weng
Abstract: The effect of SrO/BaO ratio on the phase structure of the (1-x)BaO.xSrO.0.7TiO2.0.3Nb2O5 composite ceramics was investigated by XRD and SEM. The results showed that the SrO/BaO ratio increased in the perovskite phase and kept almost constant in the tungsten bronze phase as the content of SrO increased in the composite system. The constant SrO/BaO ratio in the tungsten bronze phase was about 0.667. The crystal lattices of the perovskite phase in the composite system were larger and smaller respectively than that in pure (1-x)BaO.xSrO.TiO2 system when SrO/BaO ratio were respectively <0.667 and >0.667. The crystal lattices of the perovskite phases in both systems showed the same crystal lattices when SrO/BaO = 0.667. Affected by the SrO/BaO ratio required in the tungsten bronze phase in composite system, the contents and average grain size of the perovskite phase decreased, while the content of tungsten bronze phase increased as the SrO/BaO ratio increased.
Authors: Jian Fei Wang, Yuan Hua Lin, Yu Chen, Lei Jiang, Ce Wen Nan
Abstract: NiO-NiTiO3 composite ceramics were prepared by the conventional solid state reaction process and dielectric properties were investigated as a function of frequency and temperature. The results indicate that all samples showed high dielectric constant ~103 at 0.1 kHz, but a remarkable decrease of the dielectric loss appeared when the volume fraction of NiTiO3 phase reached 42.4%. Relaxor-like peaks were observed in the temperature dependence of the dielectric constant with ceramics having low composition of NiTiO3 phase (≤21.2%). The possible response mechanism associated with the microstructure and the associated defects of the composites was discussed.
Authors: Yan Ping Lu, Ming Shi
Abstract: TiO2-Al2O3 composite ceramics prepared by high temperature sintering in H2 atmosphere exhibit good microwave-absorbing behavior at high frequencies. In this paper, dielectric properties of TiO2-Al2O3 composite ceramic at high frequencies, which are correlated with its microwaveabsorbing characteristics, were measured by wave-guide reflective transmitting method. Effects of additives such as MnO2, CaO, SiO2, sintering process and atmosphere on high frequency dielectric properties of TiO2-Al2O3 composite ceramic were investigated.
Authors: Chang Shu Xiang, Xiao Mei Shi, Yu Bai Pan, Jing Kun Guo
Abstract: Stable and disperse carbon nanotubes (CNTs) aqueous solution was prepared by using cetyltrimethylammonium bromide (C16TMAB) as dispersing agent and zeta potential of CNTs solution were measured to quantitatively characterize the stability of CNTs in C16TMAB aqueous solution. The CNTs /SiO2 composites were fabricated with composite powders synthesized by rapid Sol-gel method and sintered by hot-pressing technique. The electric and dielectric properties of the composites were measured and the microstructure of CNTs and composites were investigated by Field emission scanning electron microscope (FSEM) and transmission electron microscopy (TEM). The mechanisms had been investigated to explain the effect of the CNT compositions on the electric and dielectric properties of CNTs /SiO2 composites in this paper.
Authors: Xiang Yu Zhang, Shou Hong Tan, Wei-Wei Xu, Shao Ming Dong, Zheng Ren Huang, Ye Dong, Pei-Heng Wu, Dong Liang Jiang
Abstract: The microstructure and microwave dielectric properties of inhomogeneous SiC-AlN solid solutions, hot pressed under a pressure of 40 MPa, have been investigated. Microstructure analysis detected the existence of BN in the resulted samples, which may be a reason that homogeneous solid solution was not formed for the samples with AlN content higher than 20%. The dc resistivity of the solid solutions at room temperature varies from 8 × 103 Ω m to 1 × 109 Ω m. Ion jump and dipole relaxation losses are the main mechanism of dielectric losses.
Authors: Shao Hong Wang, He Ping Zhou, Ke Xin Chen, Xiao Shan Ning
Abstract: Preparation technology and sintering characteristics of the CaO-Al2O3-B2O3-SiO2 system glass ceramics were investigated. Results showed that the glass ceramics of this system could be sintered at 850oC; the material has fine sintering properties, outstanding dielectric properties including low dielectric constant (about 4.85, 1GHz) and low dielectric loss (about 0.1%, 1GHz). XRD analysis indicated that the crystalline phases in the sintered body are mainly Al5(BO3)O6, a trace amount of SiO2 and CaSiO3.
Authors: Yong Zhang, Ai Li Ding, Xi Yun He, Zi Ping Cao, Qing Rui Yin
Abstract: Polycrystalline dysprosium (Dy) doped PLZT ceramics with compositional formula [Pb0.88 (La1-xDyx)0.12](Zr0.40 Ti0.60)O3] were prepared by hot-pressed solid-state method. Dy3+ concentration x varied from 0 to 0.5. All samples present single phase with tetragonal structure and the tetragonality was increased with increasing Dy3+ content. The Raman spectra indicated that Dy3+ ions could be distributed in both A and B site of ABO3 perovskite structure depending on the doping amounts.
Authors: Lei Chen, Xiao Hui Wang, Long Tu Li, Zhi Lun Gui
Abstract: Titanate ferroelectric materials play more and more important roles in electronic industry due to their particular performances, so the synthesis of ultra-fine ferroelectric powder with high purity is the key issue to improve the performance of electronic components. In this paper, Ba(Ti0.85Zr0.15)O3 nano-powder with perovskite structure and homogeneous granularity was prepared by oxalate precipitation method, the particle size of the powder calcined at 800oC is about 50 nm. The sintering ability of the powder is excellent so that the compact ceramics can be obtained at sintering temperature of 1200°C, which is much lower than that of the powder prepared by the conventional solid method. With the powder prepared by oxalate precipitation method, we developed an ultrafine-grained dielectric material showing Y5V characteristics with the room temperature dielectric constant over 14,000, which can be used in base metal electrodes multilayer chip capacitors.
Authors: Jun Jie Hao, Xiao Hui Wang, Long Tu Li, Zhi Lun Gui
Abstract: The family of bismuth layer-structured ferroelectrics is attractive from the viewpoint of their application as electronic materials such as dielectrics, piezoelectrics and pyroelectrics. However, during conventional sintering method, high sintering temperature and long sintering time were needed and it is difficult to get BIT ceramic with a density more than 95% of its theoretic value. In the present paper, we produce dense BIT pellet using a spark plasma sintering process. The results show that at a sintering temperature as low as 7000C/5min under a pressure of 25MPa, BIT ceramics with a density about 99% of its theoretic can be produced. The densities, grain size and electrical properties of the resulting ceramic were also investigated.
Authors: Ping Huang, Ting Xian Xu, Feng Hou, Qiang Zou
Abstract: Strontium bismuth titanate (SBTi) matrix composites containing Ag particles were synthesized by the conventional solid-state reaction method. The SBTi/Ag composites have been characterized by various techniques: x-ray diffraction, optical metallurgical microscope, scanning electron microscope and dielectric measurement. It is found that Ag doping significantly affect the physical properties of composites. By adding Ag particles to the SBTi matrix, the single-phase layered perovskite structure of the matrix is preserved and the sintering temperature of the system decrease from 1120°C of the single-phase SBTi to 950°C of the SBTi/Ag composites. With the increase of sintering temperature, the size of silver particles increase, but the SBTi grains have no significant growth. The SBTi/Ag composites show a significant change of the dielectric constant. By increasing Ag content, a gradual increase of the dielectric constant is observed and the dielectric loss of the SBTi/Ag composites remain unchanged when the temperature rangers from room temperature to 200°C, however, the Curie peak of dielectric constant is repressed, which has been interpreted based on the effective dielectric fields developed around conducting phases and the inhibition effect of nonferroelectric secondary phase to electro-strain.

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