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Gang Du Ruihong LiangLi Wang Kui LiWenbin Zhang Genshui WangXianlin Dong 《Ceramics International》2013
The frequency, electric field cycling and temperature dependences of the polarization–electric field (P–E), strain–electric field (S–E) loops in poled Mn-doped 0.05Pb(Mn1/3Sb2/3)O3–0.50PbZrO3–0.45PbTiO3 ceramics have been investigated. The P–E and S–E loops are strongly asymmetric corresponding to the presence of an internal bias field Ei after poling and aging, indicating that the domain walls are strongly pinned by preferentially oriented defect dipoles formed by the acceptor dopant ions (Mn2+/Mn3+) and O2− vacancies. Whereas, the loops exhibit a tendency of changing from asymmetric shapes to normal symmetric ones with increasing electric field amplitude or decreasing frequency. Repeated electric field cycling as well as high temperature results in a similar effect. Meanwhile, the Ei reduces consequently, providing evidence of domain depinning or internal bias field relaxation. It is suggested that the reorientation of the defect dipoles and depinning of domain walls arising from high temperature or electric field cycling are responsible for this extrinsic internal bias field relaxation process. 相似文献
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This study investigated the production of M140, aligned multi-walled carbon nanotubes (A-MWNTs) reinforced M140 composites
(A-MWNTs-M140) and their mechanical properties including their compressive and bending properties as well as their microstructure
characteristic of bend fracture surface. M140 was first produced by speed change mixing technics with commercial materials,
water-bath curing at normal temperature. In addition, two different A-MWNTs dispersions including carbonyl dispersions of
A-MWNTs (C-A-MWNTs) and aqueous dispersions of A-MWNTs (A-A-MWNTs) with the addition of 0.01wt% A-MWNTs were utilized to obtain
enhanced mechanical properties with respect to plain M140. The results indicated that the use of A-MWNTs dispersions allows
increasing compressive strength and flexural strength by 8.4% and 5.4%, respectively for the C-A-MWNTs-M140, and by 15.9%
and 20.7% for the A-A-MWNTs-M140, respectively. The SEM and EPMA examinations of fracture surface also showed that the bond
interface between the nanotubes and matrix is moderate and the main reinforcing mechanisms are microfilling effect, CNTs pull-out
and debond. The aqueous dispersion of A-MWNTs is an appropriate method and is more compatible with the M140.
Supported by the National Natural Science Foundation of China (Grant No. 50438010) 相似文献
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Carbon free composites Li1−xMgxFePO4 (x = 0.00, 0.02) were synthesized from LiOH, H3PO4, FeSO4 and MgSO4 through hydrothermal route at 180 °C for 6h followed by being fired at 750 °C for 6 h. The samples were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), flame atomic absorption spectroscopy and electronic conductivity measurement. To investigate their electrochemical properties, the samples were mixed with glucose as carbon precursors, and fired at 750 °C for 6 h. The charge–discharge curves and cycle life test were carried out at 23 ± 2 °C. The Rietveid refinement results of lattice parameters of the samples indicate that the magnesium ion has been successfully doped into the M1 (Li) site of the phospho-olivine structure. With the same order of magnitude, there is no material difference in terms of the electronic conductivities between the doped and undoped composites. Conductivities of the doped and undoped samples are 10−10 S cm−1 before being fired, 10−9 S cm−1 after being fired at 750 °C, and 10−1 S cm−1 after coated with carbon, respectively. Both the doped and undoped composites coated with carbon exhibit comparable specific capacities of 146 mAh g−1 vs. 144 mAh g−1 at 0.2 C, 140 mAh g−1 vs. 138 mAh g−1 at 1 C, and 124 mAh g−1 vs. 123 mAh g−1 at 5 C, respectively. The capacity retention rates of both doped and undoped samples over 50 cycles at 5 C are close to 100% (vs. the first-cycle corresponding C-rate capacity). Magnesium doping has little effects on electronic conductivity and electrochemical properties of LiFePO4 composites prepared via hydrothermal route. 相似文献
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Jun LiangLi Li 《Materials Letters》2011,65(2):285-288
Novel α-Zn3(PO4)2·4H2O hierarchical sphere structures have been synthesized by a simple chemical method through the reaction between zinc acetate and orthophosphoric acid by using cetyltrimethylammonium bromide (CTAB) as capping reagent at room temperature. The structures and morphologies of the as-obtained products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The influences of the synthetic parameters on the morphologies of the final products were investigated. The experimental results clearly show that both the concentration of CTAB aqueous solution and the concentration of initial reagents play important roles in the formation of the α-Zn3(PO4)2·4H2O hierarchical sphere structure. Detailed proofs indicated that the process of crystal growth was dominated by a self-assembly growth mechanism. 相似文献
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Metabolomics is a rapidly evolving field for studying biological systems and discovering potential disease biomarkers. For any metabolomics application, metabolome analysis with adequate sensitivity and specificity is essential in defining the metabolome. Ideally, all metabolites present in a biological system are qualitatively and quantitatively profiled. Unfortunately, due to technical limitations, only a fraction of metabolites are currently analyzed by using techniques such as NMR and mass spectrometry (MS). Due to limited metabolome coverage, many important metabolome networks and some subdue changes in the metabolome may not be revealed with current techniques. In this presentation, several technical issues related to the development of LC/MS for enabling metabolome analysis will be discussed. Because of great diversity of chemical and physical properties of metabolites, we have been developing an isotope labeling LC/MS workflow with a goal of improving the metabolome coverage in analyzing biological samples such as human biofluids and tissue samples. Several labeling chemistries will be described to provide isotope tags to the metabolites for sensitive detection and accurate quantification. LC methods including multi-dimensional separation to separate the labeled metabolites with high efficiency will be discussed. New protocols for MS analysis, metabolite identification and quantitative data processing will be presented. 相似文献
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