The motion of partial dislocations, with b = 1/3[01•0> and 1/3[10•0>, was analyzed during basal slip, (00•1) 1/3<11•0>, in sapphire. Crystallographic considerations suggested that the basal slip plane was one which passed through the normally vacant octahedral sites that were defined by the anion sub-lattice. This implied that half of the cations which lay between 2 adjacent anion layers were above the slip plane, while the other half were below the slip plane. The stacking faults that were created by the motion of a dissociated basal dislocation differed in structure and energy; depending upon whether the 1/3[10•0> partial was leading or trailing. Thus, the motion of a 1/3[10•0> partial in its favored (lower-energy) direction created a stacking fault with a stacking sequence in which the cations were in localized twin symmetry. The motion of a 1/3[10•0> partial in its unfavorable (higher-energy) direction was forbidden. Finally, the motion of a 1/3[10•0> partial in its favorable direction could occur without any need for synchro-shear.

J.B.Bilde-Sørensen, B.F.Lawlor, T.Geipel, P.Pirouz, A.H.Heuer, K.P.D.Lagerlöf: Acta Materialia, 1996, 44[5], 2145-52