Preparation and Anti⁃arc Erosion Property of Ag Matrix Electrical Contact Material Reinforced by Novel Ti_(2)Cd

Due to their outstanding electrical contact properties,Cd-containing silver-matrix electrical contact materials can meet the requirements of high stability and long life for military defense and aerospace applications.In order to further reduce the Cd content under the premise of meeting the high-performance requirements,in this study,high-purity intermediate Ti_(2)Cd powder of MAX phase(Ti_(2)CdC)was synthesized with a pressureless technique and then applied to reinforce the Ag matrix.The Cd content of the as-prepared Ag/Ti_(2)Cd composites was actually reduced by 38.31%compared with conventional Ag/CdO material.Based on the systematic study of the effect of heat treatment temperature on the physical phase,morphology,interface and comprehensive physical properties of Ag/Ti_(2)Cd composites,the preferred samples(heat treated at 400°C for 1 h)showed high density(97.77%),low resistivity(2.34μΩ·cm),moderate hardness(90.8HV),high tensile strength(189.9 MPa),and exhibited good electrical contact performance after 40000 cycles of arc discharging under severe conditions(DC 28 V/20 A).The results of microscopic morphological evolution,phase change and elemental distribution of the electrical contact surface show that the combination of high stability of Ti_(2)Cd reinforcing phase,good interfacial bonding with Ag matrix and improved melt pool viscosity in the primary stage of arc erosion,results in low and stable contact resistance(average value 13.20 mΩ)and welding force(average value 0.6 N),low fluctuation of static force(2.2-2.5 N).The decomposition and absorption energy of Ti_(2)Cd and the arc extinguishing effect of Cd vapor are the main reasons for the stable arcing energy and arcing time of electric contacts in the late stage of arc erosion.

Testing results analysis of contact materials’electrical contact performance

Because of the different ways in which contact materials work, the basic requirements for silver metal oxide contact materials are different. They are anti-welded and anti-erosion when closed, anti-erosion when broken, and arc easily moved and have smaller contact resistance. In this paper, La2O3 is used as a stable oxide in contact material to replace CdO. A new type of Ag/SnO2-La2O3-Bi2O3 contact material is first obtained through using powder metallurgical method. Then electrical contact material parameter tester is used to test the electrical contact performance of the contact material. Through experiments, the arcing voltage and current curves, arcing energy curves, fusion power curves while broken and contact resistance while closed were obtained. Analysis of the results showed that the addition of La2O3 makes the contact material have the following advantages: smaller electrical wear, smaller arc energy, smaller contact resistance and arc is more easily extinguished.

Preparation of in-situ Cu/NbC nanocomposite and its functionally graded behavior for electrical contact applications

Cu–15%NbC (volume fraction) powder was synthesized using the starting powders of Cu, Nb and graphite in a high energy vibratory disc mill for 7 h of milling under argon atmosphere. A composite sample and a Cu/NbC functionally graded material (FGM) sample were produced by using the two-step press and sintering at 900 °C for 1 h under vacuum. The microstructure and physical and mechanical properties of the specimens were investigated. The field emission scanning electron microscopy, energy dispersive X-ray and X-ray diffraction analysis confirmed the synthesis of the nanostructure matrix of 18–27 nm with the nanoparticles reinforcement of 42 nm after sintering, verifying the thermal stability of this composite at high temperature. The hardness of Cu–15%NbC was five times greater than that of the pure Cu specimen. The volume reduction of the sample after the wear test decreased in comparison with the pure Cu specimen. The electrical conductivity of the composite specimen decreased to 36.68% IACS. The FGM specimen exhibited high electrical conductivity corresponding to 75.83% IACS with the same hardness and wear properties as those of the composite sample on the composite surface. Thus, Cu/NbC FGM with good mechanical and electrical properties can be a good candidate for electrical contact applications.

Evaluation of the Electrical Contact Area at the SOFC Cathode

In the frame of the ZeuS-Ill project, a model study was started on evaluation the area-specific resistances （ASRs） of various layers being used in SOFC stacks. It is well known that stack performance not only depends on cell resistance but also on the electrical conductivity of the various applied contact and protective layers. Various layers have been tested under simulated SOFC conditions, and results have shown that the lowest ASR value, about 3 mΩ.cm2, was obtained for an LSM （2） contact layer. A significantly higher resistance was found for the combined contact and protective layer LCC10-Mn3O4, being around 37 mΩ.cm2 Related to the various tests, the total ASR of an F-design stack, developed by Forschungszentrum Jiilich, under ideal conditions can be estimated. In this case the ASR value was calculated as the sum of that of the LCC10-Mn3O4 layer and the formed oxide scale due to oxidation of Crofer22APU. Contacting resistance at the anode side was considered negligible. When differences in the ASR values occurred when compared with that from current-voltage measurements performed with real SOFC stacks, this can be explained by the limited contact area between interconnect and cathode. These results can be used to model the influence of various applied layers and different geometric contact areas on the overall ASR as determined from performance measurements with SOFC stacks.

The Electro-Physical Properties of Rhenium Chalcogenides＇ Thin Films

The electro-physical properties of thin layers of rhenium chalcogenides＇ alloys, their dynamical and static ampere-voltaic characteristics were investigated. During the investigation of static and dynamical ampere-voltaic characteristics of rectifying contact of aluminium and rhenium chalcogenides＇ alloys the switching effects were found.

Enhancing back interfacial contact by in-situ prepared MoO_3 thin layer for Cu_2ZnSnS_xSe_(4–x) solar cells

In-situ prepared MoO3 thin layer has been introduced to suppress the formation of too thick Mo(S,Se)2layer in Cu2ZnSnSxSe4–x(CZTSSe) solar cells. This MoO3 layer effectively improves the back interfacial contact between CZTSSe absorber layer and Mo substrate without poisoning the carrier transport. Up to 10.58% power conversion efficiency has been achieved.

Characterization of individual grain boundaries and grains of CaCu_3Ti_4O_(12) ceramic

Microcontact measurement is employed to locally investigate the electric and dielectric properties of individual grains and grain boundaries in CaCu3Ti4O12 ceramic. The measurements give more detail of the impedance spectroscopy, capacitance, and I-V characteristics of the microstructure, and will help with further understanding of the mechanism of the electric and dielectric properties of CaCu3Ti4O12 ceramics.

A High Performance Cobalt-Doped ZnO Visible Light Photocatalyst and Its Photogenerated Charge Transfer Properties

Highly photocatalytically active cobalt-doped ZnO （ZnO：Co） nanorods have been prepared by a facile hydrothermal process. X-ray diffraction, X-ray photoelectron spectroscopy, Raman scattering and UV-vis diffuse reflectance spectroscopy confirmed that the dopant ions substitute for some of the lattice zinc ions, and furthermore, that Co〉 and Co〉 ions coexist. The as-prepared ZnO：Co samples have an extended light absorption range compared with pure ZnO and showed highly efficient photocatalytic activity, only requiring 60 rain to decompose -93% of alizarin red dye under visible light irradiation （λ 〉 420 nm）, The photophysical mechanism of the visible photocatalytic activity was investigated with the help of surface photovoltage spectroscopy. The results indicated that a strong electronic interaction between the Co and ZnO was present, and that the incorporation of Co promoted the charge separation and enhanced the charge transfer ability and, at the same time, effectively inhibited the recombination of photogenerated charge carriers in ZnO, resulting in high visible light photocatalytic activity.

Hf_(0.5)Zr_(0.5)O_(2)-based ferroelectric memristor with multilevel storage potential and artificial synaptic plasticity

Memristors are designed to mimic the brain’s integrated functions of storage and computing,thus breaking through the von Neumann framework.However,the formation and breaking of the conductive filament inside a conventional memristor is unstable,which makes it difficult to realistically mimic the function of a biological synapse.This problem has become a main factor that hinders memristor applications.The ferroelectric memristor overcomes the shortcomings of the traditional memristor because its resistance variation depends on the polarization direction of the ferroelectric thin film.In this work,an Au/Hf0.5Zr0.5O2/p+-Si ferroelectric memristor is proposed,which is capable of achieving resistive switching characteristics.In particular,the proposed device realizes the stable characteristics of multilevel storage,which possesses the potential to be applied to multi-level storage.Through polarization,the resistance of the proposed memristor can be gradually modulated by flipping the ferroelectric domains.Additionally,a plurality of resistance states can be obtained in bidirectional continuous reversibility,which is similar to the changes in synaptic weights.Furthermore,the proposed memristor is able to successfully mimic biological synaptic functions such as long-term depression,long-term potentiation,paired-pulse facilitation,and spike-timing-dependent plasticity.Consequently,it constitutes a promising candidate for a breakthrough in the von Neumann framework.

Fabrication of 150-nm Al_(0.48)In_(0.52)As/Ga_(0.47)In_(0.53)As mHEMTs on GaAs substrates

High performance 150-nm gate-length metamorphic Al0.48In0.52As/Ga0.47In0.53 As high electron mobility transistors(mHEMTs) with very good device performance have been successfully fabricated.A T-shaped gate is fabricated by using a combined technique of optical and e-beam photolithography,which is beneficial to decreasing parasitic capacitance and parasitic resistance of the gate.The ohmic contact resistance R c is as low as 0.03 mm when using a novel ohmic contact metal system(Ni/Ge/Ti/Au).The devices exhibit excellent DC and RF performance.A peak extrinsic transconductance of 775 mS/mm and a maximum drain current density of 720 mA/mm are achieved.The unity current gain cut-off frequency(fT) and the maximum oscillation frequency(f max) are 188.4 and 250 GHz,respectively.