Extra variable in grain boundary description

Abstract

Grain boundaries (GBs) are internal interfaces in crystalline materials that control many physical properties. While GBs are traditionally described by five crystallographic angles, recent atomistic simulations have shown that variations in the atomic density \ensuremath{\lambda} of \ensuremath{\Sigma}5 GBs can cause transformations between different GB phases. Here, the authors demonstrate that the multiplicity of GB phases is not specific to the particular \ensuremath{\Sigma}5 GBs studied previously. Instead, the emergence of new GB phases is a generic phenomenon that must take place in almost every GB. Thus, \ensuremath{\lambda} should be added to the description of all GBs as an extra thermodynamic parameter whose variations may cause structural phase transformations. This realization may motivate further experimental and theoretical studies of GB thermodynamics and GB phase transformations in crystalline materials.