Materials Data on Ge4Te7As2 by Materials Project
Ge4As2Te7 is Caswellsilverite-like structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of three Ge4As2Te7 sheets oriented in the (0, 0, 1) direction. there are two inequivalent Ge4+ sites. In the first Ge4+ site, Ge4+ is bonded to six Te2- atoms to form GeTe6 octahedra that share corners with three equivalent GeTe6 octahedra, corners with three equivalent AsTe6 octahedra, edges with three equivalent AsTe6 octahedra, and edges with nine GeTe6 octahedra. The corner-sharing octahedra tilt angles range from 2–4°. There are three shorter (2.94 Å) and three longer (3.05 Å) Ge–Te bond lengths. In the second Ge4+ site, Ge4+ is bonded to six Te2- atoms to form a mixture of edge and corner-sharing GeTe6 octahedra. The corner-sharing octahedra tilt angles range from 0–2°. There are three shorter (2.97 Å) and three longer (3.00 Å) Ge–Te bond lengths. As1- is bonded to six Te2- atoms to form AsTe6 octahedra that share corners with three equivalent GeTe6 octahedra, edges with three equivalent GeTe6 octahedra, and edges with six equivalent AsTe6 octahedra. The corner-sharing octahedral tilt angles are 4°. There are three shorter (2.84 Å) and three longer (3.08 Å) As–Te bond lengths. There are four inequivalent Te2- sites. In the first Te2- site, Te2- is bonded in a 3-coordinate geometry to three equivalent As1- atoms. In the second Te2- site, Te2- is bonded to three equivalent Ge4+ and three equivalent As1- atoms to form a mixture of edge and corner-sharing TeGe3As3 octahedra. The corner-sharing octahedral tilt angles are 3°. In the third Te2- site, Te2- is bonded to six equivalent Ge4+ atoms to form a mixture of edge and corner-sharing TeGe6 octahedra. The corner-sharing octahedral tilt angles are 1°. In the fourth Te2- site, Te2- is bonded to six Ge4+ atoms to form a mixture of edge and corner-sharing TeGe6 octahedra. The corner-sharing octahedra tilt angles range from 1–3°.