DOE OSTI2020
Ge3Bi2Te6 is MAX Phase-like structured and crystallizes in the trigonal R3m space group. The structure is two-dimensional and consists of three Ge3Bi2Te6 sheets oriented in the (0, 0, 1) direction. there are three inequivalent Ge2+ sites. In the first Ge2+ site, Ge2+ is bonded to six Te2- atoms to form a mixture of distorted edge and corner-sharing GeTe6 octahedra. The corner-sharing octahedral tilt angles are 15°. There are three shorter (2.85 Å) and three longer (3.44 Å) Ge–Te bond lengths. In the second Ge2+ site, Ge2+ is bonded to six Te2- atoms to form GeTe6 octahedra that share corners with three equivalent BiTe6 octahedra, edges with three equivalent BiTe6 octahedra, and edges with six equivalent GeTe6 octahedra. The corner-sharing octahedral tilt angles are 6°. There are three shorter (2.84 Å) and three longer (3.32 Å) Ge–Te bond lengths. In the third Ge2+ site, Ge2+ is bonded to six Te2- atoms to form distorted GeTe6 octahedra that share corners with three equivalent GeTe6 octahedra, corners with three equivalent BiTe6 octahedra, edges with three equivalent BiTe6 octahedra, and edges with nine GeTe6 octahedra. The corner-sharing octahedra tilt angles range from 6–15°. There are three shorter (2.85 Å) and three longer (3.33 Å) Ge–Te bond lengths. 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 GeTe6 octahedra, corners with three equivalent BiTe6 octahedra, edges with three equivalent GeTe6 octahedra, and edges with nine BiTe6 octahedra. The corner-sharing octahedra tilt angles range from 1–6°. There are three shorter (3.07 Å) and three longer (3.25 Å) Bi–Te bond lengths. In the second Bi3+ site, Bi3+ is bonded to six Te2- atoms to form BiTe6 octahedra that share corners with three equivalent GeTe6 octahedra, corners with three equivalent BiTe6 octahedra, edges with three equivalent GeTe6 octahedra, and edges with nine BiTe6 octahedra. The corner-sharing octahedra tilt angles range from 1–6°. There are three shorter (3.06 Å) and three longer (3.28 Å) Bi–Te bond lengths. There are six inequivalent Te2- sites. In the first Te2- site, Te2- is bonded to six Ge2+ atoms to form a mixture of distorted edge and corner-sharing TeGe6 octahedra. The corner-sharing octahedral tilt angles are 13°. In the second Te2- site, Te2- is bonded in a 3-coordinate geometry to three equivalent Ge2+ atoms. In the third Te2- site, Te2- is bonded to three equivalent Ge2+ and three equivalent Bi3+ atoms to form TeGe3Bi3 octahedra that share corners with six TeBi6 octahedra and edges with twelve TeGe3Bi3 octahedra. The corner-sharing octahedra tilt angles range from 4–13°. In the fourth Te2- site, Te2- is bonded to six Bi3+ atoms to form a mixture of edge and corner-sharing TeBi6 octahedra. The corner-sharing octahedra tilt angles range from 4–5°. In the fifth Te2- site, Te2- is bonded in a 3-coordinate geometry to three equivalent Ge2+ atoms. In the sixth Te2- site, Te2- is bonded to three equivalent Ge2+ and three equivalent Bi3+ atoms to form a mixture of edge and corner-sharing TeGe3Bi3 octahedra. The corner-sharing octahedral tilt angles are 5°.