A pressure induced semiconductor-semimetal phase transition on tungsten diselenide has been studied using in situ electrical resistivity measurement and first-principles calculation under high pressure. The experimental results indicate that the phase transition takes place at 38.1 GPa. The first-principles calculations performed by CASTEP code based on the density functional theory illustrate that the indirect band gap of WSe 2 vanishes at 35 GPa, which results in an isostructural phase transition from semiconductor to semimetal in WSe 2 . According to the pressure dependence of partial density of states, the semimetallic character of WSe 2 is mainly caused by W-Se covalent bonding rather than van der Waals bonding.
We carried out the accurate in situ Hall-effect measurements, the temperature dependence of electrical resistivity measurements and the first-principles calculations in SnO under high pressure. The results of Hall-effect measurements display the carrier transport behavior of SnO under pressure, which indicates that SnO undergoes a carrier-type inversion around 1.3 GPa and an underlying phase transition at 2–3 GPa. In addition, the temperature dependence of electrical resistivity shows that SnO undergoes a semiconductor-to-metal transition around 5 GPa. The calculated band structures based on the first-principles method illustrate that the indirect band gap of SnO vanishes around 4 GPa. In particular, the results of total and partial density of states indicate that the closure of the indirect fundamental gap is mostly attributed to Sn-5s and 5p states hybridized with O-2p states at the Fermi level.
The electrical contact resistance of cambered surface contact is systematically studied by analytical solution and finite-element simulation. Two representative cambered surface contacts, namely sphere-plane contact and cylinder-plane contact are built and the distributions of electrical current lines profile and isopotential are compared explicitly. Subsequently, the effects of size parameters of cambered surface and mechanical load on contact resistance are evaluated over a large range of aspect ratios. Furthermore, dissimilarity between sphere-plane contact and cylinder-plane contact is deduced.
The electromagnetic relay, which has mechanical structure and break/make contacts, is affected by vibration and shock environment greatly. Contact wear and failure will be result from serious mechanical conditions. The samples used in this study were relays consisting two spring sets connected with armature component. Simulation results for a variety of vibration levels, frequencies, and shock levels are presented. Thereafter main factors and threshold conditions which influencing contact reliability were determined by the modal analysis and the harmonic response analysis and transient response analysis. The vibration and shock characteristics of movable parts within relay were also obtained by using high speed camera PhantomV7.3 10000fps , thus the mechanism of contact failure is revealed clearly. In addition, the characteristics of contact resistance were investigated when relay working in the mechanical environment. The results are valuable in modeling characteristics degradation and contact failure evaluation caused by mechanical environment for electromagnetic relay.
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