First-Principles Study on the Cu–Cr Interfaces in Vacuum Circuit Breaker Contacts

Based on the experimental phenomenon that the breakdown position of the CuCr contact head in a vacuum circuit breaker may be the Cu–Cr phase boundary, the Cu–Cr interfacial binding models have been developed. The work function, work of interfacial separation, interfacial energy, charge transfer, and charge density distribution of Cu, Cr and W, Fe, Ni and Mo doped Cu/Cr interfaces are calculated from the first principles. The CuCr interface junction was found to have a smaller work function than pure copper and pure chromium. The reduced work function is prone to field emission, thus increasing the possibility of electrical breakdown. Three interfacial binding models Cu(110)/Cr(110), Cu(111)/Cr(111) and Cu(110)/Cr(100) are established in this paper. By comparing the separation work and interfacial energy, it is found that Cu(111)/Cr(111) is relatively stable. The charge transfer is ordered as W > Mo > Ni > Fe from large to small. This order is roughly the same as the atomic numbers of the four metals. The doping of W, Fe, Ni and Mo to make their work function reach the expected value is ranked as W > Ni > Fe > Mo. In this paper, we provide a theoretical basis for increasing the voltage strength of vacuum circuit breakers.