Figure 1.
Sketch of the atomic structure of Bi2 X 3 (X = Se, Te). Panel (a) shows the stacking of the basal planes for the two twin modifications. A unit cell consists of 15 atomic planes which are grouped into three quintuples. A dashed line marks a horizontal twin plane which separates twins 1 and 2 and marks the moment of a change of the stacking order, which is indicated. Panel (b) shows the top view of the two twin modifications. The unit-cell parameters c and a are indicated in panels (a) and (b), respectively.