DOI: 10.17188/1270897
title: Materials Data on Na4TiAs2O9 by Materials Project

description: Na4TiAs2O9 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are four inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded to six O2- atoms to form distorted NaO6 octahedra that share corners with two equivalent TiO6 octahedra, corners with two equivalent AsO4 tetrahedra, edges with two equivalent NaO6 octahedra, and edges with two equivalent AsO4 tetrahedra. The corner-sharing octahedral tilt angles are 57°. There are a spread of Na–O bond distances ranging from 2.41–2.55 Å. In the second Na1+ site, Na1+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Na–O bond distances ranging from 2.21–2.68 Å. In the third Na1+ site, Na1+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Na–O bond distances ranging from 2.20–2.55 Å. In the fourth Na1+ site, Na1+ is bonded to six O2- atoms to form NaO6 octahedra that share corners with two equivalent TiO6 octahedra, corners with two equivalent AsO4 tetrahedra, edges with two equivalent NaO6 octahedra, and edges with two equivalent AsO4 tetrahedra. The corner-sharing octahedral tilt angles are 62°. There are a spread of Na–O bond distances ranging from 2.42–2.55 Å. Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with two equivalent TiO6 octahedra, corners with four NaO6 octahedra, and corners with four AsO4 tetrahedra. The corner-sharing octahedra tilt angles range from 35–62°. There are a spread of Ti–O bond distances ranging from 1.90–2.03 Å. There are two inequivalent As5+ sites. In the first As5+ site, As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share corners with two equivalent NaO6 octahedra, corners with two equivalent TiO6 octahedra, and edges with two equivalent NaO6 octahedra. The corner-sharing octahedra tilt angles range from 49–62°. There are a spread of As–O bond distances ranging from 1.69–1.76 Å. In the second As5+ site, As5+ is bonded to four O2- atoms to form AsO4 tetrahedra that share corners with two equivalent NaO6 octahedra, corners with two equivalent TiO6 octahedra, and edges with two equivalent NaO6 octahedra. The corner-sharing octahedra tilt angles range from 50–64°. There is two shorter (1.70 Å) and two longer (1.76 Å) As–O bond length. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two Na1+, one Ti4+, and one As5+ atom. In the second O2- site, O2- is bonded to three Na1+ and one As5+ atom to form distorted edge-sharing ONa3As trigonal pyramids. In the third O2- site, O2- is bonded in a 2-coordinate geometry to two Na1+ and two equivalent Ti4+ atoms. In the fourth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to three Na1+ and one As5+ atom. In the fifth O2- site, O2- is bonded in a 4-coordinate geometry to two Na1+, one Ti4+, and one As5+ atom. In the sixth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to three Na1+ and one As5+ atom. In the seventh O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to three Na1+ and one As5+ atom.