DOE OSTI2020
Ge5Te4Se is Caswellsilverite-like structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. there are three inequivalent Ge2+ sites. In the first Ge2+ site, Ge2+ is bonded to six Te2- atoms to form a mixture of edge and corner-sharing GeTe6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.97 Å) and two longer (3.03 Å) Ge–Te bond lengths. In the second Ge2+ site, Ge2+ is bonded to five Te2- and one Se2- atom to form a mixture of edge and corner-sharing GeTe5Se octahedra. The corner-sharing octahedra tilt angles range from 0–1°. There are four shorter (2.97 Å) and one longer (3.05 Å) Ge–Te bond lengths. The Ge–Se bond length is 2.99 Å. In the third Ge2+ site, Ge2+ is bonded to two equivalent Te2- and four equivalent Se2- atoms to form GeTe2Se4 octahedra that share corners with six GeTe6 octahedra and edges with twelve GeTe5Se octahedra. The corner-sharing octahedral tilt angles are 0°. Both Ge–Te bond lengths are 3.02 Å. All Ge–Se bond lengths are 2.97 Å. There are two inequivalent Te2- sites. In the first Te2- site, Te2- is bonded to six Ge2+ atoms to form TeGe6 octahedra that share corners with six TeGe6 octahedra, edges with four equivalent SeGe6 octahedra, and edges with eight TeGe6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. In the second Te2- site, Te2- is bonded to six Ge2+ atoms to form TeGe6 octahedra that share a cornercorner with one SeGe6 octahedra, corners with five TeGe6 octahedra, and edges with twelve TeGe6 octahedra. The corner-sharing octahedral tilt angles are 0°. Se2- is bonded to six Ge2+ atoms to form SeGe6 octahedra that share corners with two equivalent TeGe6 octahedra, corners with four equivalent SeGe6 octahedra, edges with four equivalent SeGe6 octahedra, and edges with eight equivalent TeGe6 octahedra. The corner-sharing octahedral tilt angles are 0°.