DOE OSTI2020
Eu2Cd2As3 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent Eu+2.50+ sites. In the first Eu+2.50+ site, Eu+2.50+ is bonded to six As3- atoms to form EuAs6 octahedra that share corners with six equivalent EuAs7 pentagonal bipyramids, corners with seven CdAs4 tetrahedra, edges with four equivalent EuAs6 octahedra, an edgeedge with one EuAs7 pentagonal bipyramid, edges with five CdAs4 tetrahedra, and a faceface with one EuAs7 pentagonal bipyramid. There are a spread of Eu–As bond distances ranging from 3.06–3.19 Å. In the second Eu+2.50+ site, Eu+2.50+ is bonded to seven As3- atoms to form distorted EuAs7 pentagonal bipyramids that share corners with six equivalent EuAs6 octahedra, corners with seven CdAs4 tetrahedra, an edgeedge with one EuAs6 octahedra, edges with four equivalent EuAs7 pentagonal bipyramids, edges with three CdAs4 tetrahedra, a faceface with one EuAs6 octahedra, and faces with three equivalent EuAs7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 37–47°. There are a spread of Eu–As bond distances ranging from 3.10–3.46 Å. There are two inequivalent Cd2+ sites. In the first Cd2+ site, Cd2+ is bonded to four As3- atoms to form CdAs4 tetrahedra that share corners with three equivalent EuAs6 octahedra, corners with three equivalent EuAs7 pentagonal bipyramids, corners with four CdAs4 tetrahedra, edges with three equivalent EuAs6 octahedra, edges with two equivalent EuAs7 pentagonal bipyramids, and edges with two equivalent CdAs4 tetrahedra. The corner-sharing octahedra tilt angles range from 13–56°. There are a spread of Cd–As bond distances ranging from 2.73–2.79 Å. In the second Cd2+ site, Cd2+ is bonded to four As3- atoms to form CdAs4 tetrahedra that share corners with four equivalent EuAs6 octahedra, corners with four equivalent EuAs7 pentagonal bipyramids, corners with four CdAs4 tetrahedra, edges with two equivalent EuAs6 octahedra, an edgeedge with one EuAs7 pentagonal bipyramid, and edges with three CdAs4 tetrahedra. The corner-sharing octahedra tilt angles range from 16–58°. There are a spread of Cd–As bond distances ranging from 2.70–2.95 Å. There are three inequivalent As3- sites. In the first As3- site, As3- is bonded in a 8-coordinate geometry to six Eu+2.50+, one Cd2+, and one As3- atom. The As–As bond length is 2.56 Å. In the second As3- site, As3- is bonded in a 7-coordinate geometry to four Eu+2.50+ and three Cd2+ atoms. In the third As3- site, As3- is bonded to three equivalent Eu+2.50+ and four Cd2+ atoms to form distorted edge-sharing AsEu3Cd4 pentagonal bipyramids.