DOE OSTI2020
Bi2Te2S 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 six Te2- atoms to form BiTe6 octahedra that share corners with three equivalent BiTe3S3 octahedra and edges with nine BiTe6 octahedra. The corner-sharing octahedral tilt angles are 2°. There are three shorter (3.06 Å) and three longer (3.31 Å) Bi–Te bond lengths. In the second Bi3+ site, Bi3+ is bonded to three equivalent Te2- and three equivalent S2- atoms to form distorted BiTe3S3 octahedra that share corners with three equivalent BiTe6 octahedra, corners with three equivalent TeBi3S3 octahedra, edges with three equivalent TeBi3S3 octahedra, and edges with nine BiTe6 octahedra. The corner-sharing octahedra tilt angles range from 2–20°. All Bi–Te bond lengths are 3.24 Å. All Bi–S bond lengths are 2.81 Å. There are two inequivalent Te2- sites. In the first Te2- site, Te2- is bonded to six Bi3+ atoms to form TeBi6 octahedra that share corners with three equivalent TeBi3S3 octahedra and edges with nine TeBi6 octahedra. The corner-sharing octahedral tilt angles are 6°. In the second Te2- site, Te2- is bonded to three equivalent Bi3+ and three equivalent S2- atoms to form TeBi3S3 octahedra that share corners with three equivalent BiTe3S3 octahedra, corners with three equivalent TeBi6 octahedra, edges with three equivalent BiTe3S3 octahedra, and edges with nine TeBi6 octahedra. The corner-sharing octahedra tilt angles range from 6–20°. All Te–S bond lengths are 3.70 Å. S2- is bonded in a 6-coordinate geometry to three equivalent Bi3+ and three equivalent Te2- atoms.