High resolution and conventional electron microscopy studies of repeated wedge microtwins in monoclinic rare earth sesquioxides

Abstract

SummaryHigh resolution and conventional studies have been made on the inclined twin boundaries occurring near the tip of wedge microtwins in the case of repeated wedge microtwins occurring at twin intersections. These inclined boundaries appear to be continuous and all the atomic planes are also continuous so that we suggest the use of the term ‘inclined coherent boundaries’ instead of ‘incoherent’ which one generally employs, in analogy to the case of precipitates in a matrix. This is different from what occurs in the case of isolated wedge microtwins for the same material and for the same kind of twins where the inclined twin boundary is really not coherent, being made of non‐inclined coherent regions separated by steps containing a dislocation.The coherent inclined boundaries of repeated wedge microtwins appear to be rotated about two perpendicular axes of the habit plane (tilt and twist) giving rise to a distribution of microdislocations whose role has been studied. The values of the tilt and twist angles are related to a minimization of the total energy by a mechanism that is likely to appear only in the case of thin foils. A comparative study of the different roles related to the different structures of inclined twin boundaries for isolated and repeated wedge microtwins has been made, and also a comparative study of the mechanisms of stress relaxation in each case. The studies have been made on (313) twins of a monoclinic samarium sesquioxide.