Materials Data on Na4SrCaSi2 by Materials Project
(Na)2Na2SrCaSi2 is alpha bismuth trifluoride-derived structured and crystallizes in the tetragonal P-4m2 space group. The structure is three-dimensional and consists of two sodium molecules and one Na2SrCaSi2 framework. In the Na2SrCaSi2 framework, there are two inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded to four equivalent Si4- atoms to form NaSi4 tetrahedra that share corners with four equivalent CaSi4 tetrahedra, corners with twelve NaSi4 tetrahedra, edges with two equivalent CaSi4 tetrahedra, and edges with four equivalent SrSi4 tetrahedra. All Na–Si bond lengths are 3.27 Å. In the second Na1+ site, Na1+ is bonded to four equivalent Si4- atoms to form NaSi4 tetrahedra that share corners with four equivalent SrSi4 tetrahedra, corners with twelve NaSi4 tetrahedra, edges with two equivalent SrSi4 tetrahedra, and edges with four equivalent CaSi4 tetrahedra. All Na–Si bond lengths are 3.20 Å. Sr2+ is bonded to four equivalent Si4- atoms to form SrSi4 tetrahedra that share corners with four equivalent NaSi4 tetrahedra, corners with four equivalent SrSi4 tetrahedra, corners with eight equivalent CaSi4 tetrahedra, and edges with six NaSi4 tetrahedra. All Sr–Si bond lengths are 3.27 Å. Ca2+ is bonded to four equivalent Si4- atoms to form CaSi4 tetrahedra that share corners with four equivalent NaSi4 tetrahedra, corners with four equivalent CaSi4 tetrahedra, corners with eight equivalent SrSi4 tetrahedra, and edges with six NaSi4 tetrahedra. All Ca–Si bond lengths are 3.20 Å. Si4- is bonded in a body-centered cubic geometry to four Na1+, two equivalent Sr2+, and two equivalent Ca2+ atoms.