Figure 1.

The crystal structure of Bi₂Te_3−xSe_x is comprised of quintuple layers of X⁽¹⁾ − Bi − X⁽²⁾ − Bi − X⁽¹⁾ where X represents either Te or Se and the number in parentheses designates between the two inequivalent sites. The X⁽²⁾ site is preferentially occupied by Se, and the alloy forms an ordered compound at the Bi₂Te₂Se composition.