Figure 3
From: Modulations in martensitic Heusler alloys originate from nanotwin ordering
Schematic view how minimizing the total interaction energy results in a transition from a disordered arrangement of nanotwins to periodic 14M arrangements connected by mesoscopic a14M/b14M twin boundaries. a) Starting point was an irregular arrangement of nanotwin boundaries (dotted lines) connecting two different orientations of the tetragonal building blocks (marked in light and dark blue). b) Without changing the number of building blocks for each direction, an almost regular arrangement was possible, which minimised the interaction energy. This is illustrated for the 14M martensite exhibiting an ideal \({(2\bar{5})}_{2}\) stacking sequence. Though at both sides of the a14M/b14M twin boundary (TB) a \({(2\bar{5})}_{2}\) stacking occurs, on the left side these are two light and five dark variants and on the right side five light and two dark ones. Thus, the orientation of the 14M unit cells (marked in red) is mirrored by the a14M/b14M twin boundary.
