Fig. 1: Crystal structures.

a The tetradymite compounds can be viewed as quintuple layers (QLs) held together by van der Waals (vdW) forces, where five atomic sites (A, B, C, D, E) are marked. b Four configurations and their mole contents for the ternary tetradymite \({{{\mathrm{Bi}}}}_{1.2}{{{\mathrm{Sb}}}}_{0.8}{{{\mathrm{Te}}}}_3\).