DOI: 10.17188/1731570
title: Materials Data on Tm2MgSe4 by Materials Project

description: MgTm2Se4 crystallizes in the triclinic P-1 space group. The structure is two-dimensional and consists of one MgTm2Se4 sheet oriented in the (0, 0, 1) direction. there are two inequivalent Mg2+ sites. In the first Mg2+ site, Mg2+ is bonded to four Se2- atoms to form MgSe4 tetrahedra that share a cornercorner with one MgSe6 octahedra, corners with two equivalent TmSe6 octahedra, and corners with six TmSe4 tetrahedra. The corner-sharing octahedra tilt angles range from 59–60°. There are a spread of Mg–Se bond distances ranging from 2.57–2.62 Å. In the second Mg2+ site, Mg2+ is bonded to six Se2- atoms to form MgSe6 octahedra that share a cornercorner with one MgSe4 tetrahedra, corners with five TmSe4 tetrahedra, edges with two equivalent MgSe6 octahedra, and edges with four equivalent TmSe6 octahedra. There are a spread of Mg–Se bond distances ranging from 2.81–2.85 Å. There are four inequivalent Tm3+ sites. In the first Tm3+ site, Tm3+ is bonded to four Se2- atoms to form TmSe4 tetrahedra that share a cornercorner with one TmSe6 octahedra, corners with two equivalent MgSe6 octahedra, corners with two equivalent MgSe4 tetrahedra, and corners with four TmSe4 tetrahedra. The corner-sharing octahedra tilt angles range from 58–61°. There are a spread of Tm–Se bond distances ranging from 2.66–2.71 Å. In the second Tm3+ site, Tm3+ is bonded to six Se2- atoms to form TmSe6 octahedra that share corners with two equivalent MgSe4 tetrahedra, corners with four TmSe4 tetrahedra, edges with two equivalent TmSe6 octahedra, and edges with four equivalent MgSe6 octahedra. There are a spread of Tm–Se bond distances ranging from 2.83–2.91 Å. In the third Tm3+ site, Tm3+ is bonded to four Se2- atoms to form TmSe4 tetrahedra that share a cornercorner with one TmSe6 octahedra, corners with two equivalent MgSe6 octahedra, corners with two equivalent MgSe4 tetrahedra, and corners with four TmSe4 tetrahedra. The corner-sharing octahedra tilt angles range from 58–63°. There are a spread of Tm–Se bond distances ranging from 2.66–2.72 Å. In the fourth Tm3+ site, Tm3+ is bonded to four Se2- atoms to form TmSe4 tetrahedra that share a cornercorner with one MgSe6 octahedra, corners with two equivalent TmSe6 octahedra, corners with two equivalent MgSe4 tetrahedra, and corners with four TmSe4 tetrahedra. The corner-sharing octahedra tilt angles range from 58–61°. There are a spread of Tm–Se bond distances ranging from 2.67–2.71 Å. There are eight inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to two equivalent Mg2+ and two Tm3+ atoms to form distorted SeTm2Mg2 tetrahedra that share corners with seven SeTm3Mg tetrahedra, corners with two equivalent SeTm2Mg2 trigonal pyramids, edges with two SeTm2Mg2 tetrahedra, and an edgeedge with one SeTm2Mg2 trigonal pyramid. In the second Se2- site, Se2- is bonded to two Mg2+ and two equivalent Tm3+ atoms to form distorted SeTm2Mg2 trigonal pyramids that share corners with nine SeTm2Mg2 tetrahedra, edges with two SeTm3Mg tetrahedra, and an edgeedge with one SeTm2Mg2 trigonal pyramid. In the third Se2- site, Se2- is bonded in a trigonal non-coplanar geometry to one Mg2+ and two Tm3+ atoms. In the fourth Se2- site, Se2- is bonded in a trigonal non-coplanar geometry to three Tm3+ atoms. In the fifth Se2- site, Se2- is bonded in a trigonal non-coplanar geometry to one Mg2+ and two Tm3+ atoms. In the sixth Se2- site, Se2- is bonded in a trigonal non-coplanar geometry to one Mg2+ and two Tm3+ atoms. In the seventh Se2- site, Se2- is bonded to one Mg2+ and three Tm3+ atoms to form distorted SeTm3Mg tetrahedra that share corners with six SeTm2Mg2 tetrahedra, corners with three equivalent SeTm2Mg2 trigonal pyramids, edges with two SeTm3Mg tetrahedra, and an edgeedge with one SeTm2Mg2 trigonal pyramid. In the eighth Se2- site, Se2- is bonded to two equivalent Mg2+ and two Tm3+ atoms to form distorted SeTm2Mg2 tetrahedra that share corners with five SeTm2Mg2 tetrahedra, corners with four equivalent SeTm2Mg2 trigonal pyramids, and edges with three SeTm3Mg tetrahedra.