The Orientation of Electrical Breakdown Paths in Single Crystals

Abstract

The effect of temperature on the orientation of electrical breakdown paths in the alkali halide crystals has been investigated. The results obtained suggest the existence of a path sequence $\mathrm{random}\ensuremath{\rightarrow}[100]\ensuremath{\rightarrow}[111]\ensuremath{\rightarrow}[110]\ensuremath{\rightarrow}[\mathrm{xxy}]$assumed by the direction of breakdown as the lattice energy or temperature increases. Star patterns of 12 non-primitive lattice directions were observed in LiCl and LiF. Mixed and impure crystals grown from the melt tend to exhibit high temperature path patterns at low temperatures. By extending the study at room temperature to crystals possessing different bonding and symmetry properties, general laws governing path orientation are established. It is shown that the possible path directions depend upon the macroscopic symmetry prevailing and are apparently not influenced by the type of lattice bond.