Electron microscope observations of deformed magnesium oxide

Abstract Observations have been made by electron transmission microscopy of thin flakes of deformed magnesium oxide. The ease of cross slip of screw dislocations in this material has been directly verified. Cross slip leads to the formations of many markedly elongated prismatic loops of dislocation. These are observed Profusely within slip bands, produced at room temperature. They are unstable at higher temperatures and break up into numbers of smaller prismatic loops. From these observations a mechanism for the widening of slip bands, observed under the optical microscope, is proposed. Certain dislocation interactions have been observed and analysed and preliminary observations made of slip band intersections.