A Layered Tin Bismuth Selenide with Three Different Building Blocks that Account for an Extremely Large Lattice Parameter of 283 Å

The layered compound Sn(2.8(4))Bi(20.2(4))Se(27) exhibits an extraordinarily long‐periodic 150R stacking sequence. The crystal structure contains three different building blocks, which form upon the addition of Sn to a Bi‐rich bismuth selenide. Sn‐doped Bi(2) double (“2”) layers similar to those in elemental bismuth, Sn(0.3)Bi(1.7)Se(3) quintuple (“5”) layers and Sn(0.4)Bi(2.6)Se(4) septuple (“7”) layers are arranged in a 7525757525|7525757525|7525757525 sequence, which corresponds to a structure with a=4.1819(4) and c=282.64(6) Å in space group R [Formula: see text] m. The structure of a microcrystal was determined using microfocused synchrotron radiation and refined as a formally commensurately modulated structure in (3+1)D superspace (superspace group R [Formula: see text] m(00γ)00), with a trivial basic structure that contains just one atom. The stacking sequence as well as the cation distribution are confirmed by aberration‐corrected scanning transmission electron microscopy (STEM) in combination with chemical mapping by X‐ray spectroscopy with atomic resolution. Stacking faults are not typical but have been observed occasionally.