  A model based on dislocation glide controlled by the nucleation and
propagation of kink pairs in a high Peierls stress crystal is revisited and
modified to account for changes in dislocation densities and segment lengths
with temperature and stress. It is applied to the critical resolved shear
stress (CRSS) for basal and prism plane slip in sapphire (alpha-Al2O3).
According to agreed-upon knowledge on dislocations in sapphire, basal slip and
prism plane slip are modelled with undissociated and dissociated dislocations,
respectively. In the latter case, partial dislocations move independently.
Amongst a number of sets of fitting parameters, good fits between experimental
and modelled CRSS9s are obtained in the long segment limit over the whole range
of temperatures by making use of physically sound parameters, including a
stress dependence of the dislocation density.
