Transmission electron-microscopic studies on mechanisms for dipole formation in MgO

Abstract

To obtain more detailed information of the mechanism for dipole formation, dislocation structures have been observed in magnesium oxide single crystals, commercially pure and doped with cobalt oxide, titanium oxide or zirconium oxide, using specimens cut parallel to the slip planes. Most dislocation dipoles are extremely long (i.e. ≥ 1 μ) and are concluded to be produced by a collision mechanism, because only this mechanism can explain simultaneously the formation of three-fold dipole nodes, of extremely long dipoles of mixed character and the association of a single dipole with a precipitate. Direct evidence for the operation of a rearrangement mechanism has been obtained. The dipoles produced by this mechanism are relatively short (i.e. ≤0·5 μ) and few.