4. Conclusion
We studied the atomic-scale characteristics of edge dislocation in 5 polymorphs of dicalcium silicate, as a class of complex low symmetry oxides. While our experimental TEM tests revealed a clear high-resolution image of edge dislocation in C2S, we performed extensive computations to provide an “atomistic lens” on edge dislocation characteristics. We found that γ-C2S and α-C2S polymorphs have the lowest core formation energies and thus the most favorable polymorphs for dislocations in dicalcium silicates, mainly due to their large pore channels and nearly rigid-body type movements of atoms, which take away majority of the distortions imposed by edge dislocations. Our results suggest that α-C2S crystal is the most reactive polymorph in dislocation-mediated crystal growth, consistent with previous reports. Furthermore, we identified β-C2S as the most brittle polymorph of belite in the context of edge dislocation. These basic knowledge of brittleness may influence micro cracking, brittleness and fracture of belite, and combined with other strategies such as use of polymers, may help devise strategies to reduce the energy associated with grinding dicalcium silicate (cement) clinkers. This information, in conjunction with the predicted nucleation rate of reactivity, core structures and displacement fields, can provide new physical insights and guiding hypotheses for experimentalist to tune the cement reactivity processes as well as grinding mechanisms. To our knowledge, this work is the first report of atomistic-scale analysis of edge dislocations in structurally complex dicalcium silicates, and can potentially open up new opportunities for further studies, such as mixed dislocation-mediated mechanisms, brittle-to-ductile transitions, and twinning deformations and their interactions with dislocations, to provide a comprehensive understanding of deformation mechanisms in cement clinkers. Broadly, the concepts, methods and strategies of this work can impact several other oxides and low symmetry crystals such as jennite [38], layered and hybrid calcium-silicate materials [71–75], as well as recently developed realistic and combinatorial models of calcium-silicate–hydrates [76–78] and microporous materials in general [79–80].
