Figure 2
From: Modulations in martensitic Heusler alloys originate from nanotwin ordering
Oscillating interface energy of nanotwin boundaries γtot separated by n martensitic building blocks. The γtot of ideal symmetric \((n\bar{n})\) twins (triangles) was decomposed into the oscillations interaction of nanotwins, γn, at small n, and into a constant contribution γ∞ at large n. The latter describes the pure nanotwin boundary formation energy. The martensitic building blocks had a tetragonal distortion of c/a|NM = 1.26. Asymmetric \({(n\bar{m})}_{2}\) arrangements (diamonds) could be predicted from the superposition of the respective γtot obtained from the symmetric \((n\bar{n})\) and \((m\bar{m})\) cases (crosses), proving the additive relation. We used n + m = 14 building blocks where the twin boundaries were separated by n and m = 14 − n building blocks, respectively. As this geometry contains twice as many nanotwin boundaries compared to the symmetric one, the offset was 2 × γ∞. Upon structural optimisation (circles), γtot decreased rather uniformly, i.e. independent of n, indicating that relaxations were confined to the interface.
