DOE OSTI2020
Eu3(SiAs2)2 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are three inequivalent Eu2+ sites. In the first Eu2+ site, Eu2+ is bonded to six As+1.50- atoms to form EuAs6 octahedra that share corners with four EuAs6 octahedra, corners with eight SiSiAs3 tetrahedra, edges with eight EuAs6 octahedra, and an edgeedge with one SiSiAs3 tetrahedra. The corner-sharing octahedra tilt angles range from 2–9°. There are a spread of Eu–As bond distances ranging from 3.06–3.23 Å. In the second Eu2+ site, Eu2+ is bonded to six As+1.50- atoms to form EuAs6 octahedra that share corners with four EuAs6 octahedra, corners with four SiSiAs3 tetrahedra, edges with nine EuAs6 octahedra, and edges with two equivalent SiSiAs3 tetrahedra. The corner-sharing octahedra tilt angles range from 2–7°. There are a spread of Eu–As bond distances ranging from 3.06–3.23 Å. In the third Eu2+ site, Eu2+ is bonded to six As+1.50- atoms to form EuAs6 octahedra that share corners with four EuAs6 octahedra, corners with four SiSiAs3 tetrahedra, edges with nine EuAs6 octahedra, and edges with two SiSiAs3 tetrahedra. The corner-sharing octahedra tilt angles range from 3–9°. There are a spread of Eu–As bond distances ranging from 3.06–3.15 Å. There are two inequivalent Si sites. In the first Si site, Si is bonded to one Si and three As+1.50- atoms to form distorted SiSiAs3 tetrahedra that share corners with three AsEu4Si2 octahedra, corners with eight EuAs6 octahedra, a cornercorner with one SiSiAs3 tetrahedra, and edges with three EuAs6 octahedra. The corner-sharing octahedra tilt angles range from 18–79°. The Si–Si bond length is 2.38 Å. There are a spread of Si–As bond distances ranging from 2.37–2.48 Å. In the second Si site, Si is bonded to one Si and three As+1.50- atoms to form SiSiAs3 tetrahedra that share corners with three AsEu5Si octahedra, corners with eight EuAs6 octahedra, corners with three SiSiAs3 tetrahedra, and edges with two EuAs6 octahedra. The corner-sharing octahedra tilt angles range from 13–81°. There are one shorter (2.42 Å) and two longer (2.45 Å) Si–As bond lengths. There are four inequivalent As+1.50- sites. In the first As+1.50- site, As+1.50- is bonded to four Eu2+ and two equivalent Si atoms to form AsEu4Si2 octahedra that share corners with eight AsEu4Si2 octahedra, corners with two equivalent SiSiAs3 tetrahedra, and edges with eight AsEu4Si2 octahedra. The corner-sharing octahedra tilt angles range from 1–93°. In the second As+1.50- site, As+1.50- is bonded to five Eu2+ and one Si atom to form AsEu5Si octahedra that share corners with seven AsEu4Si2 octahedra, a cornercorner with one SiSiAs3 tetrahedra, and edges with ten AsEu4Si2 octahedra. The corner-sharing octahedra tilt angles range from 1–89°. In the third As+1.50- site, As+1.50- is bonded to four Eu2+ and two Si atoms to form AsEu4Si2 octahedra that share corners with eight AsEu4Si2 octahedra, corners with two SiSiAs3 tetrahedra, and edges with eight AsEu4Si2 octahedra. The corner-sharing octahedra tilt angles range from 4–94°. In the fourth As+1.50- site, As+1.50- is bonded to five Eu2+ and one Si atom to form AsEu5Si octahedra that share corners with seven AsEu4Si2 octahedra, a cornercorner with one SiSiAs3 tetrahedra, and edges with ten AsEu4Si2 octahedra. The corner-sharing octahedra tilt angles range from 2–93°.