First-principles calculations on slip system activation in the rock salt structure: electronic origin of ductility in silver chloride

Abstract

First principles calculations were performed to understand an electronic origin of high ductility in silver chloride (AgCl) with the rock salt structure. From calculations of generalised stacking fault energies for different slip systems, it was found that only the {1 1 0} slip system is favourably activated in sodium chloride (NaCl) with the same rock salt structure, whereas AgCl shows three kinds of possible slip systems along the direction on the {0 0 1}, {1 1 0}, and {1 1 1} planes, which is in excellent agreement with experiment. Detailed analyses of the electronic structures across slip planes showed that the more covalent character of bonding of Ag–Cl than Na–Cl tends to make the slip motion energetically favourable. It was also surprising to find out that strong Ag–Ag covalent bonds across the slip plane are formed in the {0 0 1}〈1 1 0〉 slip system in AgCl, which makes it possible to activate the multiple slip systems in AgCl.

Keywords:

• Plasticity of crystals
• ionic crystals
• first-principles calculations
• generalised stacking fault (GSF)
• crystal orbital Hamilton population (COHP)