A mirror-symmetry glide structure was observed at Σ = 9 [01¯1]/(122) tilt boundaries. No mirror-symmetry unit was found which was consistent with the observation that the mirror symmetry unit had a higher energy in low stacking-fault energy, or higher bulk modulus, face-centered cubic metals. The boundary width was estimated to be about 0.1241nm, and this was equal to about twice the (224) lattice spacing.

HRTEM Investigation of a Σ = 9 [01¯1]/(122) Symmetric Tilt Grain Boundary in Cu. J.R.Hu, S.C.Chang, F.R.Chen, J.J.Kai: Scripta Materialia, 2001, 45[4], 463-9