DOE OSTI2020
Sr4TiN4 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are four inequivalent Sr2+ sites. In the first Sr2+ site, Sr2+ is bonded to five N3- atoms to form distorted SrN5 trigonal bipyramids that share a cornercorner with one SrN5 square pyramid, corners with three equivalent TiN4 tetrahedra, corners with four equivalent SrN4 trigonal pyramids, edges with two equivalent SrN5 square pyramids, an edgeedge with one TiN4 tetrahedra, an edgeedge with one SrN5 trigonal bipyramid, and an edgeedge with one SrN4 trigonal pyramid. There are a spread of Sr–N bond distances ranging from 2.57–2.86 Å. In the second Sr2+ site, Sr2+ is bonded to four N3- atoms to form distorted SrN4 trigonal pyramids that share corners with two equivalent SrN5 square pyramids, corners with four equivalent TiN4 tetrahedra, corners with four equivalent SrN5 trigonal bipyramids, an edgeedge with one SrN5 trigonal bipyramid, and edges with two equivalent SrN4 trigonal pyramids. There are a spread of Sr–N bond distances ranging from 2.56–2.65 Å. In the third Sr2+ site, Sr2+ is bonded to five N3- atoms to form distorted SrN5 square pyramids that share corners with three equivalent TiN4 tetrahedra, a cornercorner with one SrN5 trigonal bipyramid, corners with two equivalent SrN4 trigonal pyramids, edges with two equivalent SrN5 square pyramids, an edgeedge with one TiN4 tetrahedra, and edges with two equivalent SrN5 trigonal bipyramids. There are a spread of Sr–N bond distances ranging from 2.58–2.72 Å. In the fourth Sr2+ site, Sr2+ is bonded in a 5-coordinate geometry to five N3- atoms. There are a spread of Sr–N bond distances ranging from 2.60–2.82 Å. Ti4+ is bonded to four N3- atoms to form TiN4 tetrahedra that share corners with three equivalent SrN5 square pyramids, corners with three equivalent SrN5 trigonal bipyramids, corners with four equivalent SrN4 trigonal pyramids, an edgeedge with one SrN5 square pyramid, and an edgeedge with one SrN5 trigonal bipyramid. There are a spread of Ti–N bond distances ranging from 1.96–2.00 Å. There are four inequivalent N3- sites. In the first N3- site, N3- is bonded to five Sr2+ and one Ti4+ atom to form a mixture of distorted corner and edge-sharing NSr5Ti octahedra. The corner-sharing octahedra tilt angles range from 17–20°. In the second N3- site, N3- is bonded in a 5-coordinate geometry to four Sr2+ and one Ti4+ atom. In the third N3- site, N3- is bonded to five Sr2+ and one Ti4+ atom to form a mixture of distorted corner and edge-sharing NSr5Ti octahedra. The corner-sharing octahedra tilt angles range from 17–20°. In the fourth N3- site, N3- is bonded in a 6-coordinate geometry to five Sr2+ and one Ti4+ atom.