Abstract
The presence of facets and line junctions connecting facets on grain boundaries (GBs) has a strong impact on the properties of structural, functional, and optoelectronic materials: They govern the mobility of interfaces, the segregation of impurities, as well the electronic properties. In the present paper, we employ density-functional theory and modified embedded atom method calculations to systematically investigate the energetics and thermodynamic stability of these defects. As a prototype system, we consider $\mathrm{\ensuremath{\Sigma}}3$ tilt GBs in Si. By analyzing the energetics of different faceted GBs, we derive a diagram that describes and predicts the reconstruction of these extended defects as a function of facet length and boundary inclination angle. The phase diagram sheds light upon the fundamental mechanisms causing GB faceting phenomena. It demonstrates that the properties of faceting are not determined solely by anisotropic GB energies but by a complex interplay between geometry and microstructure, boundary energies as well as long-range strain interactions.
Highlights
Crystal defects such as grain boundaries (GBs) severely impact materials properties [1]
We derive a phase diagram of these boundaries. This phase diagram demonstrates that (i) these GBs are intrinsically unstable against faceting toward {111} and {112} facets and (ii) the properties of the facets and of the line junctions is the result of an intricate interplay between GB energies and long-range strain interactions
The significance of being able to construct such defect phase diagrams goes beyond the case of GBs in multicrystalline Si (mc-Si)
Summary
Crystal defects such as grain boundaries (GBs) severely impact materials properties [1]. GBs often act as strong gettering centers for metal impurities due to the presence of over- or undercoordinated atoms and the different-than-bulk strain. These impurities, the over- or undercoordinated and/or highly strained host atoms may introduce deep states into the fundamental band gap. Such states would act as recombination centers and reduce the efficiency of solar cells [7]
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