Dielectric Relaxations in Ferroelectric Copolymer VDF(73)/TrFE(27)

The characteristics of molecular mtin of ferroelectric copolymer VDF(73)/TrFE(27) have been investigated by means of dielectric relaxation. With the rise in crystallinity. the Curie point decreases and the dielectric constant increases in the region of ferroelectric-to-paraelectric phase transition. The frequency spectra of the coplymer below room temperature consist of lowfrequency component ascribed to the micro-Brownian motions of molecular segments in the noncrystalline regins and high-frequency cmponent associated with the local motions of smallscale segments. By using the fitting results with one or two Cole-Cole functions, and calculating with WLF equation and Arrhenius formula, the glass transition temperature and the activation energy of local relaxation are obtained. the distribution of relaxation time in the molten and ferroelectric phases is located at a same line, and complies with Arrhenius ruIe, which suggests that the elementary motions are of same type for molecular motions provided by the hightemperature process and the low-temperature local mode process     

Electrical characterization of LiTaO<Subscript>3</Subscript>:P(VDF–TrFE) composites

Composites of pyroelectric ceramics and polymers are very important as their unique features and properties can be easily tailored for various specific applications. Lithium tantalatum oxide (LiTaO₃, LT), the pyroelectric ceramic powder has been incorporated into a polyvinylidene fluoride–trifluoroethylene [P(VDF–TrFE) 70/30 mol%] copolymer matrix to form 0–3 composites. The composite films were prepared using ‘solvent casting’ (SC) method to disperse the ceramic powder homogeneously in the P(VDF–TrFE) copolymer matrix with various wt% of LT powder. In order to derive high pyroelectric performance, the samples were poled. Electric properties, such as the dielectric constant, dielectric loss, and pyroelectric coefficient, have been measured as a function of temperature and frequency. In addition, material figures-of-merit, very important factors for assessing many sensor applications have also been calculated. The results show that the fabricated lead free lithium tantalite: P(VDF–TrFE) composite materials have a good potential for pyroelectric infrared sensor applications.     

电子辐照的P(VDF/TrFE)共聚物的铁电弛豫异常现象

本文研究了聚偏氟乙烯和三氟乙烯的铁电共聚物P(VDF/TrFE)的铁电弛豫现象,并讨论了铁电弛豫异常想象.比较了VDF不同含量的共聚物在辐照前后铁电性能的改变,电子辐照大大改变了聚合物样品的性能,使VDF含量52%和70%的样品出现了明显的铁电弛豫现象,但发现在VDF含量为80%的样品中存在一种铁电弛豫异常现象:铁电居里峰随着频率的升高而向低温端移动.研究样品的二氟乙烯(VDF)的摩尔含量在52%～80%之间.     

Solution-processed Ni–CNTs filled ferroelectric P(VDF–TrFE) composites with improved dielectric properties and thermal conductivity

Dielectric composites made using two kinds of poly(vinylidene fluoride–trifluoroethylene) [P(VDF–TrFE)] (70/30 and 80/20 mol%) as polymer matrices and nickel particles coated carbon nanotubes (Ni–CNTs) as filler were developed via solution-processed method. The scanning electron microscopy (SEM) indicated good compatibility and dispersion of Ni–CNTs in the P(VDF–TrFE) matrix. Ni–CNTs/P(VDF–TrFE) composites exhibited high dielectric constants with low dielectric losses. The maximum dielectric constants of Ni–CNTs/P(VDF–TrFE) composites of 198 and 185 at 100 Hz were obtained at 18.0 wt% Ni–CNTs loading, respectively. The incorporation of Ni–CNTs in the P(VDF–TrFE) matrix resulted in enhanced thermal conductivity. The highest values, obtained at 18.0 wt% Ni–CNTs loading, were 1.05 and 1.03 W/m K, respectively. Although there were no very obvious difference, the dielectric properties and thermal conductivity of Ni–CNTs/P(VDF–TrFE) 70/30 mol% composites were slightly better to those of Ni–CNTs/P(VDF–TrFE) 80/20 mol% composites in many cases. The aforementioned results suggest that these high-performance composites hold great promise for application in electrical and electronic field.     

基板弯曲对P( VDF - TrFE)铁电薄膜电学性能的影响

近年来基于铁电聚合物的柔性存储器件的研制受到了越来越多的关注.铁电聚合物柔性应用的关键因素之一,在于基板弯对其电学性产生多大程度的影响,但迄今这方面的研究较少.本文研究了柔性基板弯曲对铁电聚合物薄膜电学性能的影响,通过对铁电电容结构的表征,确定了基板弯曲对铁电膜矫顽场、剩余极化、电学保持能力、电学疲劳特性和漏电流特性的...     

Low-temperature superplasticity of Al2O3(p)/Ni–Co nanocomposites

Nanocomposites of Al₂O₃/Ni–Co prepared using Al₂O₃ of various particle sizes were fabricated by pulse current electrodeposition. Their superplastic tensile deformation was investigated at strain rates of 8.33 × 10⁻⁴ s⁻¹ and 1.67 × 10⁻³ s⁻¹ and temperatures of 723–823 K. The Al₂O₃ particle sizes and the deformation temperature had significant influence on the elongation of the deposited materials. The optimal superplastic condition and the maximum elongation were determined. A low temperature superplasticity with elongation of 632% was achieved at a strain rate of 1.67 × 10⁻³ s⁻¹ and 823 K. Scanning electron microscopy and transmission electron microscopy were used to examine the microstructures of the deposited and deformed samples. The grains grew to a micrometer dimensions and were elongated along the tensile direction after superplastic deformation. Superplasticity in electrodeposited nanocomposites is related to the presence of S at grain boundaries and to deformation twinning.     

A model of axial heterostructure formation in III–V semiconductor nanowires

Technical Physics Letters - A kinetic model of the formation of axial heterostructures in nanocrystalline wires (nanowires, NWs) of III–V semiconductor compounds growing according to the...     

Nitriding of Co–Cr–Mo alloy in nitrogen

Using the results of a thermodynamic analysis, a Co–Cr–Mo alloy was successfully nitrided in nitrogen at temperatures of 1073–1473 K. The near-surface microstructure of the treated Co–Cr–Mo alloy was characterized using X-ray diffraction, field-emission scanning electron microscopy, electron probe micro-analyzer, and transmission electron microscopy equipped with energy-dispersive X-ray spectroscopy. The results indicated that the highest nitriding efficiency was achieved at the treatment temperature of 1273 K, with the size and coverage of the nitride particles on sample's surface increasing with an increase in the treatment duration. After nitriding at 1273 K for 2 h, numerous nitride particles, consisting of an outer Cr₂N layer and an inner π phase layer, were formed on top of the nitrogen-containing γ phase, and some π phase also precipitated in the alloy matrix at the sub-surface level.     

Characteristics of serrated flow in commercial Cu–Be–Co alloy

Abstract

Serrated yielding in a Cu–l·8Be–0·3Co (wt-%) alloy has been studied as a function of strain rate and temperature. Serration characteristics, e.g. type, stress drop δσ, frequency ν, vacancy concentrations–strain exponent m, mobile dislocation density–strain exponent β, and activation energy Q_m for serrated yielding, have been determined. Strain rate sensitivity of flow stress δσ/? ln ? and activation volume V parameters have also been derived through strain rate change tests. The results have been interpreted in the light of the static strain aging model of the Portevin–Le Chatelier effect.

MST/540     

利用原子力显微镜改变P(VDF/TrFE)聚合物分子链偶极子极性实现数据存储的读/写/擦除/改写

包括读、写、擦除和改写等信息存储现象的产生是由于在外加电压的作用下，铁电体“聚偏二氟乙烯-三氟胸苷”异分子聚合物的分子链偶极子的极性发生了变化．为达此目的，使原子力显微镜工作在压电响应模式下，它比传统的数据存储方法要有优势．将20nm厚的“聚偏二氟乙烯-三氟胸苷”薄膜放置于原子力显微镜的导电悬臂梁触针和石墨基片之间，直流电通过AFM触针在几微秒的时间内极化铁电畴，同时用交流电来辨识这些纳米尺度(约60nm)的铁电畴，这些铁电畴的尺寸由外加电压的大小和持续时间等参数来决定，可以实现约19．2Gb／cm^2(120Gb／in^2)的数据存储．     

P(VDF/CTFE)共聚物薄膜的驻极体行为

通过不同条件下的正负电晕充电,等温表面电位衰减测量,热刺激放电（TSD）电流谱分析和热脉冲技术,首次研究了偏氟乙烯（VDF）和三氟氯乙烯（CTFE）共聚物P（VDF／CTFE）的驻极体性质,结果指出：共聚物驻极体的空间电荷热稳定性明显优于PVDF;TSD谱分析说明这种材料驻极体也是极性驻极体,即体内同时包含有偶极和空间电荷。本文还对样品的正负电晕充电后的电荷储存稳定性做了对比;研究了材料的能阱分布,确定了样品在不同温度电晕充电时平均电荷重迁移规律。     

Correlation of microstructure and magnetic properties in Cu–Co–Ni alloys

The present study concerns correlation of microstructure and magnetic properties of nanocrystalline binary 50Cu–50Co and ternary 50Cu–25Co–25Ni (wt%) alloys prepared by ball milling and subsequent isothermal annealing of the ball milled alloys. High resolution transmission electron microscopic (HR-TEM) investigation has shown deformation-induced microstructural features. Field emission scanning electron microscopy (FE-SEM) has revealed a distinct change in morphology of as-milled CuCoNi alloys after annealing. Differential scanning calorimetric (DSC) and X-ray diffraction (XRD) analysis have revealed that annealing of the CuCoNi alloy above 350 °C results into precipitation of nanocrystalline Co (fcc) in the CuNi matrix by spinodal decomposition. It is also demonstrated that isothermal annealing of the ball milled alloys in the temperature range between 350 and 650 °C significantly influence the magnetic properties, e.g. coercivity (H_c), remanence (M_r) and magnetic saturation (M_s) due to annihilation of defects such as stacking and twin fault along with dissolution and/or precipitation of magnetic phases in the Cu-rich matrix.     

Coarsening of Co-rich precipitates in a Cu–Co–Fe ternary alloy

The effect of coherency on coarsening of fcc Co–Fe precipitates in a Cu–1.47 wt.%Co–0.56 wt.%Fe (Co : Fe = 7:3 in atomic ratio) alloy aged at 873–973 K has been studied by measuring both the precipitate size by transmission electron microscopy and the solute concentration in the Cu matrix by electrical resistivity measurements. The precipitate phase consists of 7 parts of Co and 3 parts of Fe in atomic ratio, irrespective of the precipitate size. The precipitates smaller than about 8 nm in radius are coherent with the Cu-matrix. When the average precipitate radius is over 18 nm, all the precipitates become semi-coherent. The coarsening rates are not affected by the coherency of the precipitates. The precipitate/matrix interface energy γ has been derived, independently of the diffusivities of solute atoms using a coarsening model developed by Kuehmann and Voorhees for ternary systems. The precipitates are coherent or semi-coherent with the matrix, the experimentally obtained value of γ is 0.2 J/m². This value lies between the reported values of γ  = 0.15 J/m² for Co precipitates and γ = 0.25 J/m² for γ-Fe precipitates.     

Phase Relations in the Reduction of Solid Solutions in the Co–Mn–Ti–O System

The hydrogen reduction of spinel solid solutions in the Co–Mn–Ti–O system was investigated by a static method. Six phase regions were identified in which the gas phase is in equilibrium with various combinations of -Co, TiO₂ (rutile), and solid solutions of variable composition: Co _A Mn _B Ti_{3 – A – B} O₄ (spinel), Co _m Mn_{2 – m} TiO₄ (spinel), Co _N Mn_{1 – N} TiO₃ (ilmenite), and Co _n Mn_{1 – n} O (NaCl). The equilibrium compositions of the solid solutions and the corresponding oxygen partial pressures were determined, and the general trends of the reduction of spinel solid solutions in the Co–Mn–Ti–O system were established.     

Characterization of hot deformation behavior of a new Ni–Cr–Co based P/M superalloy

The hot deformation behavior of a new Ni–Cr–Co based P/M superalloy was studied in the temperature range of 950–1150 °C and strain rate range of 0.0003–1 s^? 1 using hot compression tests. It was characterized by true stress–true strain curves, constitutive equation, strain rate sensitivity m contour maps, power dissipation η maps and hot processing maps. The microstructural validation of processing maps was also done. The results show that the flow stress decreases with increasing temperature and decreasing strain rate. The hot deformation apparent activation energy of the Ni–Cr–Co based P/M superalloy at peak stress is 805 kJ/mol. The m and η contour maps are similar, and the values of m and η in the peak zones increase with increasing strain. When the strain is 0.5, a domain with its peak η of 40% and peak m of 25% occurs at 1050 °C and 0.0003 s^? 1, which corresponds to dynamic recrystallization and can be as an optimum condition for good workability.     

Electron microscopy of binder phase deformation in WC–Co alloys

Abstract

The deformation behaviour of binder phase regions in cemented carbides is studied using transmission electron microscopy. Stacking fault densities vary strongly up to the limit of complete transformation of the cubic into the hexagonal modification. Undissociated dislocations are rarely observed. Stacking fault intersections are limited to regions of low stacking fault density. All types of deformation defect are observed in undeformed specimens. These defects are caused by deformation resulting from the relaxation of residual hydrostatic stresses during foil preparation.

MST/808     

Recent progress in the structure control of Pd–Ru bimetallic nanomaterials

Pd and Ru are two key elements of the platinum-group metals that are invaluable to areas such as catalysis and energy storage/transfer. To maximize the potential of the Pd and Ru elements, significant effort has been devoted to synthesizing Pd–Ru bimetallic materials. However, most of the reports dealing with this subject describe phase-separated structures such as near-surface alloys and physical mixtures of monometallic nanoparticles (NPs). Pd–Ru alloys with homogenous structure and arbitrary metallic ratio are highly desired for basic scientific research and commercial material design. In the past several years, with the development of nanoscience, Pd–Ru bimetallic alloys with different architectures including heterostructure, core-shell structure and solid-solution alloy were successfully synthesized. In particular, we have now reached the stage of being able to obtain Pd–Ru solid-solution alloy NPs over the whole composition range. These Pd–Ru bimetallic alloys are better catalysts than their parent metal NPs in many catalytic reactions, because the electronic structures of Pd and Ru are modified by alloying. In this review, we describe the recent development in the structure control of Pd–Ru bimetallic nanomaterials. Aiming for a better understanding of the synthesis strategies, some fundamental details including fabrication methods and formation mechanisms are discussed. We stress that the modification of electronic structure, originating from different nanoscale geometry and chemical composition, profoundly affects material properties. Finally, we discuss open issues in this field.