Electron irradiation induced vitrification at dislocations in quartz
Recent observations using the ‘weak beam’ electron microscopy technique of split images of dislocations in quartz have been interpreted as arising either from dissociation of the dislocations into partials1, or from a glassy (metamict) phase at the core2, resulting from irradiation damage. In this letter we describe observations of lattice images of near end-on dislocations in quartz, which enable us to distinguish between these two models.
Effect of elastic distortions on solid-state amorphization at grain boundaries and dislocations
Two theoretical models are proposed, which describe solid-state amorphizing transformations at, respectively, grain boundaries and dislocations in crystalline solids. In the framework of the former model, the driving force for the formation of an amorphous intergranular layer is revealed and estimated, which is related to changes in the elastic energy density of a conventional grain boundary that transforms into the amorphous layer. The second model describes nucleation of the amorphous phase at the cores of lattice and interfacial dislocations as a process associated with the special splitting of such dislocations. In the framework of the model, the special role of elastic distortions in solid-state amorphization at dislocation cores is revealed and examined.
Deformation Structures in Minerals
Although it is four decades since it was proposed (Orowan, 1934; Polanyi, 1934; Taylor, 1934) that linear defects or dislocations in crystals play a major role in the plastic deformation of crystalline solids, it is little more than two decades since the existence of dislocations in crystals was established and their motions clearly associated with deformation. Direct observation of dislocations and associated deformation structures in very thin specimens by transmission electron microscopy (TEM), initially achieved by Hirsch et al. (1956) and Bollman (1956), has proved to be the most fruitful method of study. It is interesting to note that mineral crystals figured significantly in these early developments; for example, the first observations of surface growth steps at the emergence of screw dislocations on crystal surfaces were made in natural beryl crystals (Griffin, 1950); and some of the classic early TEM studies of dislocations, partial dislocations and stacking faults in layer structures were made on graphite and talc, muscovite and chlorite (Amelinckx and Delavignette, 1960 a, b, 1961), in specimens produced by cleavage. However, largely because of difficulties in producing suitably thin “foils” of minerals with poorly-developed cleavage (Tighe, Chapter 3 of this volume) TEM studies of minerals proceeded slowly until late in the 1960’s.