Materials Data on KEr2CuSe4 by Materials Project
KEr2CuSe4 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. K1+ is bonded in a 6-coordinate geometry to eight Se2- atoms. There are a spread of K–Se bond distances ranging from 3.21–3.91 Å. Er3+ is bonded to six Se2- atoms to form ErSe6 octahedra that share corners with three equivalent ErSe6 octahedra, a cornercorner with one CuSe4 tetrahedra, edges with five equivalent ErSe6 octahedra, and edges with two equivalent CuSe4 tetrahedra. The corner-sharing octahedra tilt angles range from 0–41°. There are a spread of Er–Se bond distances ranging from 2.82–2.93 Å. Cu1+ is bonded to four Se2- atoms to form CuSe4 tetrahedra that share corners with two equivalent ErSe6 octahedra, corners with two equivalent CuSe4 tetrahedra, and edges with four equivalent ErSe6 octahedra. The corner-sharing octahedral tilt angles are 7°. There are two shorter (2.45 Å) and two longer (2.47 Å) Cu–Se bond lengths. There are three inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 6-coordinate geometry to two equivalent K1+, two equivalent Er3+, and two equivalent Cu1+ atoms. In the second Se2- site, Se2- is bonded to two equivalent K1+, three equivalent Er3+, and one Cu1+ atom to form a mixture of distorted corner, edge, and face-sharing SeK2Er3Cu octahedra. The corner-sharing octahedral tilt angles are 62°. In the third Se2- site, Se2- is bonded in a distorted square co-planar geometry to two equivalent K1+ and four equivalent Er3+ atoms.