Papers by Keyword: Dielectric Property

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Authors: Da Yong Lu, Xiu Yun Sun
Abstract: The electron paramagnetic resonance (EPR) technique was employed to investigate the point defects in barium strontium titanate ceramics. All samples showed a strong EPR signal with g = 2.000, which was indexed as intrinsic Ti-vacancy defects. In (Ba0.85Sr0.15)TiO3 ceramic, which showed a tetragonal symmetry and consisted of the crystallites with average size of ~ 220 nm, a novel EPR powder spectrum was observed - the g-factor of the g = 2.000 signal evolved into a g-tensor, and the two weak signals with g3 = ~ 2.6 and g1 = ~ 1.6 gradually shifted toward the g2 = 2.000 signal and approached to each other with increasing temperature.
Authors: F.M.M. Pereira, A.S.B. Sombra
Abstract: The Ferrite term is used to refer to all magnetic oxides containing iron as major metallic component which has great to technological applications because of their ferromagnetic and insulating properties at room temperature. Among such ferrites, the hexagonal ones (hexaferrites) have long been used for permanent magnets and are of interest for microwave applications. The hexaferrite M-type has a structure built up from the S blocks interposed by the R block and are symbolically described as RSR*S*. In the last decades there has been great interest in the hexaferrites M-Type for applications as electronic components for mobile and wireless communications at microwave/GHz frequencies, electromagnetic wave absorbers for electromagnetic compatibility (EMC), radar absorting material (RAM) and stealth technologies and as composite materials. This review aimed study the structure, magnetic and dielectric properties of the hexaferrite BaxSr1-xFe12O19, which is a promising material for electronic devices and for small dielectric resonator antennas (MRA).The outline of this Review Paper is as follows:
Authors: Mi Mi Li, Shi Feng Huang, Shi Hui Xie, Mei Juan Zhou, Xin Cheng
Abstract: A carbon black modified 0–3 cement-based piezoelectric composite was fabricated with piezoelectric ceramic [0.08Pb(Li1/4Nb3/4)O•0.47PbTiO3•0.45PbZrO3], sulphoaluminate cement and carbon black by compressing technique. The influences of poling conditions on the piezoelectric and dielectric properties of the composites were investigated. The results show that the higher poling electric field, the longer poling time and the higher poling temperature, the composites have the higher piezoelectric strain factor d33, piezoelectric voltage factor g33, dielectric constant εr and dielectric loss tanδ. At the same time, the carbon black modified composites are polarized more easily than the unmodified composites, and have better piezoelectric and dielectric properties. Meanwhile, the optimum poling conditions were obtained, and the optimum poling field E, poling time t and poling temperature T were 4 kV/mm, 20 min and 80 °C.
Authors: Tan Winie, Chin Han Chan, Ri Hanum Yahaya Subban
Abstract: Hexanoyl chitosan: LiClO4: TiO2 composite electrolyte films were prepared by the solution cast technique. The ac conductivity and dielectric properties of the samples prepared have been studied in the frequency range from 100 Hz to 1 MHz over the temperature range from 273 to 333 K. The exponent s in the Jonscher’s universal power law, σ(ω)=σdc+Aωs was analyzed as a function of temperature and the analysis suggests that the conduction mechanism can be interpreted based on the correlated barrier hopping (CBH) model. The barrier heights, WM were calculated. The values of WM are found to decrease with increasing temperature in the same manner as the exponent s. Both dielectric constant and dielectric loss decrease with increase in frequency and increase with increase in temperature.
Authors: Hai Long Liang, Chun Peng Wang, Yan Li Huo, Chuan Qi Hu, Xiao Ting Huang, Jie Tang
Abstract: Highly dense AlN/CNT composite ceramics with 1-10% volume fractions of CNT were fabricated by spark plasma sintered (SPS) at 1400°C-1700°C. The results indicated that origination diameter of AlN had a great effect on microstructure and thermal conductivity. In details, for the system with AlN origination diameter of nanosized, the tubular structure of CNT has not been destructed, but when micro-sized AlN powder was adopted, the structure of CNT showed unstable at high temperature. Even though the degradation with incorporation of CNT into AlN, thermal conductivity of sintered AlN/CNT composites ceramics was evidently improved by adjusting content of additive Y2O3 and the sintering process. Both the real part and imaginary part of the composites of Ka-Band (26.540.0 GHz) increase with the increase of CNT content, in which the increase of imaginary part is more than that of real part, resulting in an increase of loss factor. The AlN/ CNT thermal conductivity composites with appropriate CNT content and sintering temperature possess good dielectric dissipation and thermal conductivity.
Authors: Yuan Yuan, Bing Xie, Yu Wang
Abstract: A series of polyimide thin films were prepared successfully based on bis[3,5-dimethyl-4- (4-aminophenoxy)phenyl]methane (BDAPM), 9,9-bis(4-(4-aminophenoxy)phenyl)fluorene (BAOFL) and different dianhydrides. And an interesting result of dielectric property for polyimide thin films was found that the polyimide thin film prepared with 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) exhibited high dielectric constants of 5.7 at 1MHz. Conversely, the other polyimides possessing fluorene groups showed low dielectric constants. The structures and the mechanical properties of polyimide films also proved the reason for results of dielectric properties.
Authors: Krit Won-In, J. Dutchaneephet, Sorapong Pongkrapan, N. Sirikulrat, Pisutti Dararutana
Abstract: Barium-bearing glass samples were fabricated in a laboratory scale using quartz sands that was a by-product of feldspar floatation in Tak Province, northern Thailand, and 30-wt% barite from Loei Province, northeastern Thailand, as the main compositions. Cr2O3 of concentrations ranging from 0.01 to 5.0 wt% was doped into the glass mixture. The dried powders were wellmixed in a ceramic crucible and melted in an electric furnace at 1250°C for 6 hr. Bubble-free glass samples were yielded after cooling down. The glass colors were changed from colorless to green by the addition of Cr2O3. Dielectric property, color, specific gravity, and refractive index of the glass samples were analyzed. It was found that dielectric constant, specific gravity, and refractive index increased with increasing amount of Cr2O3 dopant. Measurements of UV-VIS-NIR spectra and microstuctural analysis using scanning electron microscope were also carried out and discussed.
Authors: Jun Jie Hao, Xiao Hui Wang, Jian Ling Zhao, Long Tu Li
Abstract: Textured bismuth titanate ceramics were successfully produced by spark plasma sintering, using plate-like Bi4Ti3O12 particles prepared by a molten salt method. The microstructure and electric properties of the samples were investigated. The results show that the textured Bi4Ti3O12 ceramics electric property is anisotropic in different direction, and spark plasma sintering is an effective sintering technology to get textured dense Bi4Ti3O12 ceramics at a low temperature.
Authors: Gui Xia Dong, Wei Liu
Abstract: The electrical and dielectric properties of Ba0.3Sr0.7TiO3 (BST), as a function of annealed temperature and oxygen partial pressure (P(O2)) , were studied in this paper. The resistivity data were fit to a p type model involving only doubly ionized oxygen vacancies, holes, and accidental acceptor impurities, and it decreased as P(O2) and temperature increased. The breakdown strength exhibited the same trend with resistivity. The breakdown strength exhibited the same trend with resistivity. The maximum dielectric constant of BST was observed under the lowest P(O2) at the temperature of 900°C. BST annealed under P(O2) of 0.1 atm at the temperature of 800°C obtained the highest volume energy storage density.
Authors: Jing Wang, Chuan Wei Zang, Liang Ying Zhang, Xi Yao
Abstract: Conductive LaNiO3(LNO) thin films are grown on Si(100) substrates by a sol-gel method and their application as the bottom electrode for the growth of sol-gel derived Pb(Zr,Ti)O3(PZT) thin films are studied. Morphology and electrical properties of the multilayer films are characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), electrical measurements. Experiment results show LNO thin films get highly (110)-oriented perovskite-type structure. Smooth and dense surfaces are observed on LNO thin films. The dielectric properties of PZT films show that PZT/LNO films exhibit worse dielectric properties than those of the PZT/Pt thin films. And LNO thin films prepared by sol-gel methods are not suitable as bottom electrode to deposit PZT thin films. On the other hand, FTIR spectrum and pyroelectric results of LNO thin films reveal that LNO can be used as absorber layer of PT thin films infrared detector with multi-layer thin film thermal insulation structure. At 10Hz, the detectivity (D*) and the voltage response (Rv) of PT thin films are 1.11×107cm·Hz1/2/W, 1.46×103V/W respectively.
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