Tilt and twist grain boundaries

Grain boundaries are frequently classified into tilt, twist and mixed-type boundaries. However, the classification (into tilt and twist) is not a dichotomy; due to crystal symmetries, some boundaries may be concurrently tilt and twist boundaries. Formal conditions for a planar homophase boundary between crystals with m3m symmetry to be a tilt as well as a twist boundary are determined, and a procedure for verification of whether a boundary has such dual character is given.