The radius of curvature of dislocation segments in MgO crystals stressed in the high-voltage electron microscope

Abstract

Abstract MgO single crystals have been deformed inside the high-voltage electron microscope. The local radius of curvature of dislocation segments bowing out between strong obstacles was determined by photometric measurement of the dislocation coordinates and by piecewise fitting of third-order polynomials to these coordinates. While individual segments show very different dependences of the local radius of curvature on the dislocation orientation, averages over greater numbers of segments agree fairly well with theoretical results obtained using the line tension model with isotropic elasticity. During unloading, the segments have the form of almost straight sections connected by strongly curved regions, probably as a result of obstacles to their back-motion. The bowing out of the segments is influenced by interactions with neighbouring segments. The radii of curvature depend on the length of the segments. The dependence found experimentally is much stronger than is predicted theoretically; this would considerably reduce effective stresses determined from dislocation curvatures.