“…Hence, to accommodate c-axis strain, HCP structures require dislocation gliding in the non-basal directions which has a higher energy barrier. According to general consensus, the easiest non-basal dislocation to activate is the pyramidal /c þ aS (Price, 1961a;Lavrentev et al, 1968Lavrentev et al, , 1978Lavrentev and Pokhil, 1975), but it is still so difficult to activate that certain twin partials, notably those with Burgers vectors along the /1011S directions, can twice as easily accommodate either an expansion or even a reduction of the c-axis. These disparities in critical stresses of the deformation modes are mitigated with increasing temperature and/or decreasing strain rates.…”