DOE OSTI2020
Pb7Bi4Se13 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are four inequivalent Pb2+ sites. In the first Pb2+ site, Pb2+ is bonded to six Se2- atoms to form PbSe6 octahedra that share corners with four equivalent BiSe6 octahedra, edges with six PbSe6 octahedra, and edges with six equivalent BiSe6 octahedra. The corner-sharing octahedral tilt angles are 4°. There are four shorter (3.09 Å) and two longer (3.16 Å) Pb–Se bond lengths. In the second Pb2+ site, Pb2+ is bonded to six Se2- atoms to form PbSe6 octahedra that share corners with two equivalent PbSe6 octahedra, corners with two equivalent BiSe6 octahedra, a cornercorner with one PbSe7 pentagonal bipyramid, edges with five equivalent PbSe6 octahedra, edges with five equivalent BiSe6 octahedra, and edges with two equivalent PbSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 0–6°. There are a spread of Pb–Se bond distances ranging from 2.94–3.37 Å. In the third Pb2+ site, Pb2+ is bonded to six Se2- atoms to form PbSe6 octahedra that share corners with four BiSe6 octahedra, corners with four equivalent PbSe7 pentagonal bipyramids, edges with three equivalent BiSe6 octahedra, edges with four PbSe6 octahedra, and an edgeedge with one PbSe7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 2–57°. There are a spread of Pb–Se bond distances ranging from 2.99–3.23 Å. In the fourth Pb2+ site, Pb2+ is bonded to seven Se2- atoms to form distorted PbSe7 pentagonal bipyramids that share corners with four BiSe6 octahedra, corners with five PbSe6 octahedra, edges with three PbSe6 octahedra, edges with three equivalent BiSe6 octahedra, and faces with two equivalent PbSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 0–69°. There are a spread of Pb–Se bond distances ranging from 2.97–3.39 Å. There are two inequivalent Bi3+ sites. In the first Bi3+ site, Bi3+ is bonded to six Se2- atoms to form BiSe6 octahedra that share corners with five PbSe6 octahedra, corners with two equivalent PbSe7 pentagonal bipyramids, edges with four equivalent BiSe6 octahedra, and edges with six PbSe6 octahedra. The corner-sharing octahedra tilt angles range from 2–6°. There are a spread of Bi–Se bond distances ranging from 2.82–3.27 Å. In the second Bi3+ site, Bi3+ is bonded to six Se2- atoms to form BiSe6 octahedra that share a cornercorner with one BiSe6 octahedra, corners with three PbSe6 octahedra, corners with two equivalent PbSe7 pentagonal bipyramids, edges with two equivalent BiSe6 octahedra, edges with five equivalent PbSe6 octahedra, and edges with three equivalent PbSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 0–57°. There are a spread of Bi–Se bond distances ranging from 2.83–3.17 Å. There are seven inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to four equivalent Pb2+ and two equivalent Bi3+ atoms to form SeBi2Pb4 octahedra that share corners with four equivalent SeBi2Pb4 octahedra, corners with two equivalent SeBiPb3 tetrahedra, and edges with eight SeBi2Pb4 octahedra. The corner-sharing octahedral tilt angles are 2°. In the second Se2- site, Se2- is bonded to three Pb2+ and one Bi3+ atom to form distorted SeBiPb3 tetrahedra that share corners with two SeBi2Pb4 octahedra, corners with two equivalent SeBi2Pb3 square pyramids, corners with two equivalent SeBiPb3 tetrahedra, and edges with two equivalent SeBi2Pb4 octahedra. The corner-sharing octahedra tilt angles range from 2–7°. In the third Se2- site, Se2- is bonded to three Pb2+ and three equivalent Bi3+ atoms to form SeBi3Pb3 octahedra that share corners with two equivalent SeBi3Pb3 octahedra, corners with two equivalent SeBi2Pb3 square pyramids, a cornercorner with one SeBiPb3 tetrahedra, edges with five equivalent SeBi3Pb3 octahedra, and edges with five equivalent SeBi2Pb3 square pyramids. The corner-sharing octahedral tilt angles are 0°. In the fourth Se2- site, Se2- is bonded to three Pb2+ and two equivalent Bi3+ atoms to form SeBi2Pb3 square pyramids that share corners with two equivalent SeBi3Pb3 octahedra, a cornercorner with one SeBi2Pb3 square pyramid, corners with two equivalent SeBiPb3 tetrahedra, edges with five equivalent SeBi3Pb3 octahedra, and edges with two equivalent SeBi2Pb3 square pyramids. The corner-sharing octahedral tilt angles are 7°. In the fifth Se2- site, Se2- is bonded to four Pb2+ and two equivalent Bi3+ atoms to form SeBi2Pb4 octahedra that share corners with two equivalent SeBi2Pb4 octahedra, edges with seven SeBi2Pb4 octahedra, and edges with two equivalent SeBiPb3 tetrahedra. The corner-sharing octahedral tilt angles are 2°. In the sixth Se2- site, Se2- is bonded in a 5-coordinate geometry to four Pb2+ and one Bi3+ atom. In the seventh Se2- site, Se2- is bonded in a 5-coordinate geometry to three Pb2+ and two equivalent Bi3+ atoms.