DOE OSTI2020
Er2Ti3Si4 crystallizes in the tetragonal P4_12_12 space group. The structure is three-dimensional. Er3+ is bonded to seven Si4- atoms to form distorted ErSi7 pentagonal bipyramids that share corners with four equivalent TiSi6 octahedra, corners with six equivalent ErSi7 pentagonal bipyramids, corners with five equivalent TiSi6 pentagonal pyramids, edges with three equivalent ErSi7 pentagonal bipyramids, edges with two equivalent TiSi6 pentagonal pyramids, faces with two equivalent TiSi6 octahedra, faces with two equivalent ErSi7 pentagonal bipyramids, and faces with four equivalent TiSi6 pentagonal pyramids. The corner-sharing octahedra tilt angles range from 45–53°. There are a spread of Er–Si bond distances ranging from 2.81–3.10 Å. There are two inequivalent Ti+3.33+ sites. In the first Ti+3.33+ site, Ti+3.33+ is bonded to six Si4- atoms to form TiSi6 octahedra that share corners with four equivalent TiSi6 octahedra, corners with eight equivalent ErSi7 pentagonal bipyramids, corners with six equivalent TiSi6 pentagonal pyramids, faces with four equivalent ErSi7 pentagonal bipyramids, and faces with four equivalent TiSi6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 52°. There are a spread of Ti–Si bond distances ranging from 2.68–2.79 Å. In the second Ti+3.33+ site, Ti+3.33+ is bonded to six Si4- atoms to form distorted TiSi6 pentagonal pyramids that share corners with three equivalent TiSi6 octahedra, corners with five equivalent ErSi7 pentagonal bipyramids, corners with four equivalent TiSi6 pentagonal pyramids, edges with two equivalent ErSi7 pentagonal bipyramids, edges with four equivalent TiSi6 pentagonal pyramids, faces with two equivalent TiSi6 octahedra, and faces with four equivalent ErSi7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 38–41°. There are a spread of Ti–Si bond distances ranging from 2.55–2.72 Å. There are two inequivalent Si4- sites. In the first Si4- site, Si4- is bonded in a 9-coordinate geometry to four equivalent Er3+, four Ti+3.33+, and one Si4- atom. The Si–Si bond length is 2.50 Å. In the second Si4- site, Si4- is bonded in a 9-coordinate geometry to three equivalent Er3+, five Ti+3.33+, and one Si4- atom.