Search

The interface physics is very important to the electrical contact reliability of current switching devices. In this article, the arcing electrode material surface topographies are measured consecutively in the electrical endurance experiments. A novel data processing algorithm is proposed for reconstructing the real contact interface between electrodes. The characterization parameters of contact interface including ${a}$ -spots number, area, centroid distance, and contact resistance are extracted. The comparison between the experimental recorded resistance and the analytical calculation results shows the validity of the proposed method. In the electrical endurance testing, three typical evolution stages of electrical contact interface are presented and analyzed. The contact spots are limited to the surface peaks in the initial operations, and then distributed evenly across the whole electrode surface. At the end of the testing, the contact area decreases slowly with the shrinkage of central convex face. It is determined that the electrical material redistribution caused by the arc erosion is the root reason for the contact interface evolution.

Arc erosion studies are carried out on electrical contact materials in the switching current experiment. A test rig is developed to capture the 2-D image and the 3-D profile of eroded silver tin oxide electrical contact material in situ. Image processing algorithms are specially presented to accurately recognize the features of erosion region. The initial small patch of erosion traces gradually evolves into the deep crater with the increment of switching cycle enabling a study of the arc erosion behavior. 2-D image, 3-D profile, and micro surface morphologies of the eroded contacts are analyzed and then related to the extent of erosion. The results show that the evolution process of central erosion region could be divided into the enlargement in breadth of contact surface and the extension in depth of contact profile. The end result of arc erosion is the net loss of contact material, which would lead to the substantial reduction of contact force and potential electrical contact instability.

The electrical arc erosion behavior extremely limits the lifespan of electromechanical switching devices. Observation of the gradual evolution of arc erosion is highly beneficial for to understand the arc ignition and the contact degradation. In this article, the erosion of contact materials is simulated and visualized in situ with the recorded 2-D microscopic images. A novel method for erosion area identification is proposed with the combination of difference image method and mathematical morphology operations. The variation in erosion area as a function of switching current cycles is demonstrated, and the center of erosion zone that migrates continuously during the endurance experiment is determined. Finally, not only three types of arc erosion regimes (centralized arc erosion, separated arc erosion, and commutated arc erosion) are revealed, but also the associated occurrence probabilities during 1000 cycles are provided.

An alternate current impedance spectrum was utilized to differentiate the electrical transport process, respectively, in the bulk and the grain boundary of barium tungstate microcrystallines under high pressures up to 20 GPa. For powdered BaWO4microcrystallines, the grain boundary makes a more remarkable contribution than the bulk to the total resistance. The discontinuities of bulk resistance and relaxation frequency at about 7 and 14 GPa reflect the pressure-induced structural phase transitions of BaWO4from scheelite to fergusonite structure and from fergusonite to an unknown disordered structure, respectively. The activation energy of the grain boundary decreases with increasing pressure from 6.9 to 8.9 GPa, indicating that the compression has a negative contribution to the activation energy and the transport of charge carriers through the boundary becomes easier. The activation energy of the bulk also shows a similar phenomenon. In addition, the ascending relaxation frequency of the bulk and grain boundary shows that the polarization process needs much shorter time in the state of three-phase coexistence.

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.

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 WSe2vanishes at 35 GPa, which results in an isostructural phase transition from semiconductor to semimetal in WSe2. According to the pressure dependence of partial density of states, the semimetallic character of WSe2is mainly caused by W−Se covalent bonding rather than van der Waals bonding.