DOE OSTI2020
Bi2Se2Te is Caswellsilverite-like structured and crystallizes in the trigonal R3m space group. The structure is three-dimensional. there are two inequivalent Bi3+ sites. In the first Bi3+ site, Bi3+ is bonded to three equivalent Te2- and three equivalent Se2- atoms to form BiTe3Se3 octahedra that share corners with three equivalent BiSe6 octahedra and edges with nine BiTe3Se3 octahedra. The corner-sharing octahedral tilt angles are 0°. All Bi–Te bond lengths are 3.06 Å. All Bi–Se bond lengths are 3.13 Å. In the second Bi3+ site, Bi3+ is bonded to six Se2- atoms to form BiSe6 octahedra that share corners with three equivalent BiTe3Se3 octahedra, corners with three equivalent TeBi3Se3 octahedra, edges with three equivalent TeBi3Se3 octahedra, and edges with nine BiTe3Se3 octahedra. The corner-sharing octahedra tilt angles range from 0–18°. There are three shorter (2.91 Å) and three longer (3.11 Å) Bi–Se bond lengths. Te2- is bonded to three equivalent Bi3+ and three equivalent Se2- atoms to form distorted TeBi3Se3 octahedra that share corners with three equivalent BiSe6 octahedra, corners with three equivalent SeBi6 octahedra, edges with three equivalent BiSe6 octahedra, edges with three equivalent SeBi6 octahedra, and edges with six equivalent TeBi3Se3 octahedra. The corner-sharing octahedra tilt angles range from 2–18°. All Te–Se bond lengths are 3.86 Å. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to six Bi3+ atoms to form SeBi6 octahedra that share corners with three equivalent TeBi3Se3 octahedra, edges with three equivalent TeBi3Se3 octahedra, and edges with six equivalent SeBi6 octahedra. The corner-sharing octahedral tilt angles are 2°. In the second Se2- site, Se2- is bonded in a 6-coordinate geometry to three equivalent Bi3+ and three equivalent Te2- atoms.