DOE OSTI2020
Sr2Zn2As3 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent Sr2+ sites. In the first Sr2+ site, Sr2+ is bonded to six As+2.67- atoms to form SrAs6 octahedra that share corners with six equivalent SrAs7 pentagonal bipyramids, corners with seven ZnAs4 tetrahedra, edges with four equivalent SrAs6 octahedra, an edgeedge with one SrAs7 pentagonal bipyramid, edges with five ZnAs4 tetrahedra, and a faceface with one SrAs7 pentagonal bipyramid. There are a spread of Sr–As bond distances ranging from 3.12–3.17 Å. In the second Sr2+ site, Sr2+ is bonded to seven As+2.67- atoms to form SrAs7 pentagonal bipyramids that share corners with six equivalent SrAs6 octahedra, corners with seven ZnAs4 tetrahedra, an edgeedge with one SrAs6 octahedra, edges with four equivalent SrAs7 pentagonal bipyramids, edges with three ZnAs4 tetrahedra, a faceface with one SrAs6 octahedra, and faces with three equivalent SrAs7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 34–52°. There are a spread of Sr–As bond distances ranging from 3.21–3.34 Å. There are two inequivalent Zn2+ sites. In the first Zn2+ site, Zn2+ is bonded to four As+2.67- atoms to form ZnAs4 tetrahedra that share corners with three equivalent SrAs6 octahedra, corners with three equivalent SrAs7 pentagonal bipyramids, corners with four ZnAs4 tetrahedra, edges with three equivalent SrAs6 octahedra, edges with two equivalent SrAs7 pentagonal bipyramids, and edges with two equivalent ZnAs4 tetrahedra. The corner-sharing octahedra tilt angles range from 20–49°. There are a spread of Zn–As bond distances ranging from 2.56–2.68 Å. In the second Zn2+ site, Zn2+ is bonded to four As+2.67- atoms to form ZnAs4 tetrahedra that share corners with four equivalent SrAs6 octahedra, corners with four equivalent SrAs7 pentagonal bipyramids, corners with four ZnAs4 tetrahedra, edges with two equivalent SrAs6 octahedra, an edgeedge with one SrAs7 pentagonal bipyramid, and edges with three ZnAs4 tetrahedra. The corner-sharing octahedra tilt angles range from 25–55°. There are a spread of Zn–As bond distances ranging from 2.55–2.69 Å. There are three inequivalent As+2.67- sites. In the first As+2.67- site, As+2.67- is bonded in a 8-coordinate geometry to six Sr2+, one Zn2+, and one As+2.67- atom. The As–As bond length is 2.54 Å. In the second As+2.67- site, As+2.67- is bonded in a 7-coordinate geometry to four Sr2+ and three Zn2+ atoms. In the third As+2.67- site, As+2.67- is bonded to three equivalent Sr2+ and four Zn2+ atoms to form distorted edge-sharing AsSr3Zn4 pentagonal bipyramids.