Screw and edge dislocations in layered, complex oxides

Dislocations are a common type of defects that signifi cantly infl uence many mechanical phenomena such as plastic deformation, crystal growth, morphology, or diffusion of materials. Although dislocations have been well-studied for simple crystalline structures such as pure metals, semiconductors, ionic materials, and binary oxides, there is very limited knowledge on such defects in complex-layered oxides. In this work, we study the mechanisms and the infl uences of screw and edge dislocations in fi ve cement minerals, which are among the most complex-layered oxide materials. We use a cluster-based approach combined with atomistic simulations to investigate the dislocations along the interlayer direction of minerals. An analytical solution of the sextic theory regarding anisotropic materials was implemented to obtain the elastic displacement fi eld. The nonlinear deformations around the core dislocation were accurately captured by atomistic simulations. In the case of the screw dislocations in tobermorite, a natural analog of cement hydrate phase, the fi nal core has a complex 3D structure involving dramatic spiral displacements as well as formation of defected silicate chains resulting from the dislocation. Dislocation displacement map indicates an ellipsoid nonplanar spreading of the screw dislocation core extending about 40 Å in the [100] direction and 20 Å in the [010] direction. This analysis illustrates a low mobility of [001] screw dislocation in tobermorite, because any potential movement will inevitably involve silicate chain breakage. After fi tting the atomistic data to classical screw dislocation theories, the core radius is found to be 14.3 Å with a core energy of 53.7 eV/Å. For other cement minerals, we studied the correlation between the edge and screw core dislocation energies and mobilities with brittleness and correspondingly fracture energy associated with grinding cement clinker phases. This information could be used to compare and predict the prevalent defects along different directions in cement minerals, thus providing fundamental insights on deformation mechanisms governing the mechanical response of cementitious materials.