Structure and Properties of Grain Boundary in MgO Bicrystals

Abstract

Bicrystals with (100) and (110) symmetrical tilt boundaries and with (100) twist boundaries were obtained by joining two single crystals at about 2480°C without pressure. Boundary energies were measured by the thermal grooving technique at 1200 to 1600°C. It was clear that small angle boundaries lower than 10° are composed of an array of dislocations, and it was also confirmed from observation by transmission electron microscopy (TEM) in (100) twist and (110) tilt boundaries. The critical angle estimated from diffusional properties in the (100) tilt boundary was also 10°. On the other hand, the critical angle of the (100) tilt boundary following the Read-Shockley model was measured to be 20°. Up to 10° the (100) tilt boundary is composed of a straight dislocation arrangement. Above 10° boundary is composed of a crisscrossed dislocation arrangement in a kink and jog fashion. For high angle boundaries, all of the low energy boundaries observed in the (100) twist boundary and (110) tilt boundary correspond to the high density coincident site lattice (CSL) boundary. In the (100) tilt boundary, no low energy boundary was observed at higher angles because of the higher atomic density on the (100) plane than on the (110) and the introduction of dislocations with different slip systems.