The plastic deformation of α-Al2O3 single crystals having various orientations was carried out at 400 to 700C, under 1.5GPa of hydrostatic confining pressure, in order to activate basal slip and basal and rhombohedral deformation twinning. The Schmid law for basal slip was obeyed between 600 and 1500C. The stress required for basal twinning was determined, and its temperature dependence was found to be similar to that of the critical resolved shear stress for basal slip. It was suggested that the glide of dislocations through the Peierls potential controlled both basal slip and basal twinning. This supported the double cross-slip model proposed for basal twinning in sapphire.

Deformation of Sapphire (α-Al2O3) by Basal Slip and Basal Twinning below 700C. J.Castaing, A.He, K.P.D.Lagerlöf, A.H.Heuer: Philosophical Magazine, 2004, 84[11], 1113-25