DOE OSTI2020
Na4Ti3O8 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are three inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are two shorter (2.29 Å) and four longer (2.34 Å) Na–O bond lengths. In the second Na1+ site, Na1+ is bonded to six O2- atoms to form NaO6 octahedra that share corners with six equivalent TiO6 octahedra, edges with four NaO6 octahedra, and edges with four TiO6 octahedra. The corner-sharing octahedra tilt angles range from 11–15°. There are a spread of Na–O bond distances ranging from 2.42–2.52 Å. In the third Na1+ site, Na1+ is bonded to six O2- atoms to form NaO6 octahedra that share edges with four equivalent NaO6 octahedra and edges with six TiO6 octahedra. There are two shorter (2.20 Å) and four longer (2.22 Å) Na–O bond lengths. There are two inequivalent Ti4+ sites. In the first Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with six equivalent NaO6 octahedra, edges with four NaO6 octahedra, and edges with four TiO6 octahedra. The corner-sharing octahedra tilt angles range from 11–15°. There are a spread of Ti–O bond distances ranging from 1.97–2.09 Å. In the second Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share edges with four equivalent TiO6 octahedra and edges with six NaO6 octahedra. There are four shorter (1.96 Å) and two longer (2.06 Å) Ti–O bond lengths. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded to two equivalent Na1+ and three Ti4+ atoms to form ONa2Ti3 square pyramids that share corners with nine ONa3Ti2 square pyramids, edges with four equivalent ONa4Ti2 octahedra, and edges with four equivalent ONa3Ti2 square pyramids. In the second O2- site, O2- is bonded to four Na1+ and two equivalent Ti4+ atoms to form distorted ONa4Ti2 octahedra that share corners with six equivalent ONa4Ti2 octahedra and edges with twelve ONa3Ti2 square pyramids. The corner-sharing octahedral tilt angles are 0°. In the third O2- site, O2- is bonded to three Na1+ and two Ti4+ atoms to form distorted ONa3Ti2 square pyramids that share corners with nine ONa3Ti2 square pyramids, edges with four equivalent ONa4Ti2 octahedra, and edges with four ONa3Ti2 square pyramids.