Ba4Ti6Si4O25 crystallizes in the monoclinic P2/c space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 11-coordinate geometry to one O(10), one O(12), one O(2), one O(3), one O(5), two equivalent O(1), two equivalent O(4), and two equivalent O(7) atoms. In the second Ba site, Ba(2) is bonded in a 11-coordinate geometry to one O(10), one O(11), one O(2), one O(3), one O(6), two equivalent O(13), two equivalent O(8), and two equivalent O(9) atoms. There are four inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to two equivalent O(12), two equivalent O(2), and two equivalent O(6) atoms to form TiO6 octahedra that share corners with two equivalent Ti(3)O6 octahedra, corners with two equivalent Ti(4)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, and edges with two equivalent Ti(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 49-50°. In the second Ti site, Ti(2) is bonded to two equivalent O(12), two equivalent O(3), and two equivalent O(6) atoms to form TiO6 octahedra that share corners with two equivalent Ti(3)O6 octahedra, corners with two equivalent Ti(4)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, and edges with two equivalent Ti(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 50-51°. In the third Ti site, Ti(3) is bonded to one O(6), one O(9), two equivalent O(11), and two equivalent O(13) atoms to form TiO6 octahedra that share  a cornercorner with one Ti(1)O6 octahedra,  a cornercorner with one Ti(2)O6 octahedra,  a cornercorner with one Si(3)O4 tetrahedra, and edges with two equivalent Ti(3)O6 octahedra. The corner-sharing octahedral tilt angles are 50°. In the fourth Ti site, Ti(4) is bonded to one O(12), one O(7), two equivalent O(4), and two equivalent O(5) atoms to form TiO6 octahedra that share  a cornercorner with one Ti(1)O6 octahedra,  a cornercorner with one Ti(2)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, and edges with two equivalent Ti(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 49-51°. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(3), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Ti(1)O6 octahedra,  a cornercorner with one Ti(2)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles are 54°. In the second Si site, Si(2) is bonded to two equivalent O(1) and two equivalent O(7) atoms to form SiO4 tetrahedra that share corners with two equivalent Ti(4)O6 octahedra and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 56°. In the third Si site, Si(3) is bonded to two equivalent O(8) and two equivalent O(9) atoms to form SiO4 tetrahedra that share corners with two equivalent Ti(3)O6 octahedra and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 56°. There are thirteen inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to two equivalent Ba(1), one Si(1), and one Si(2) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Ba(1), one Ba(2), one Ti(1), and one Si(1) atom. In the third O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Ba(2), one Ti(2), and one Si(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to two equivalent Ba(1) and two equivalent Ti(4) atoms. In the fifth O site, O(5) is bonded in a distorted T-shaped geometry to one Ba(1) and two equivalent Ti(4) atoms. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Ba(2), one Ti(1), one Ti(2), and one Ti(3) atom. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to two equivalent Ba(1), one Ti(4), and one Si(2) atom. In the eighth O site, O(8) is bonded in a distorted bent 150 degrees geometry to two equivalent Ba(2), one Si(1), and one Si(3) atom. In the ninth O site, O(9) is bonded in a 4-coordinate geometry to two equivalent Ba(2), one Ti(3), and one Si(3) atom. In the tenth O site, O(10) is bonded in a rectangular see-saw-like geometry to two equivalent Ba(1) and two equivalent Ba(2) atoms. In the eleventh O site, O(11) is bonded in a distorted T-shaped geometry to one Ba(2) and two equivalent Ti(3) atoms. In the twelfth O site, O(12) is bonded in a distorted trigonal planar geometry to one Ba(1), one Ti(1), one Ti(2), and one Ti(4) atom. In the thirteenth O site, O(13) is bonded in a 4-coordinate geometry to two equivalent Ba(2) and two equivalent Ti(3) atoms.
Ba4Ti6Si4O25 crystallizes in the monoclinic P2/c space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 11-coordinate geometry to one O(10), one O(12), one O(2), one O(3), one O(5), two equivalent O(1), two equivalent O(4), and two equivalent O(7) atoms. The Ba(1)-O(10) bond length is 3.03 Å. The Ba(1)-O(12) bond length is 3.16 Å. The Ba(1)-O(2) bond length is 2.87 Å. The Ba(1)-O(3) bond length is 2.92 Å. The Ba(1)-O(5) bond length is 2.65 Å. There is one shorter (3.15 Å) and one longer (3.20 Å) Ba(1)-O(1) bond length. There is one shorter (2.67 Å) and one longer (3.00 Å) Ba(1)-O(4) bond length. There is one shorter (2.81 Å) and one longer (2.82 Å) Ba(1)-O(7) bond length. In the second Ba site, Ba(2) is bonded in a 11-coordinate geometry to one O(10), one O(11), one O(2), one O(3), one O(6), two equivalent O(13), two equivalent O(8), and two equivalent O(9) atoms. The Ba(2)-O(10) bond length is 3.06 Å. The Ba(2)-O(11) bond length is 2.65 Å. The Ba(2)-O(2) bond length is 2.92 Å. The Ba(2)-O(3) bond length is 2.93 Å. The Ba(2)-O(6) bond length is 3.21 Å. There is one shorter (2.66 Å) and one longer (3.00 Å) Ba(2)-O(13) bond length. There is one shorter (3.07 Å) and one longer (3.30 Å) Ba(2)-O(8) bond length. There is one shorter (2.78 Å) and one longer (2.84 Å) Ba(2)-O(9) bond length. There are four inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to two equivalent O(12), two equivalent O(2), and two equivalent O(6) atoms to form TiO6 octahedra that share corners with two equivalent Ti(3)O6 octahedra, corners with two equivalent Ti(4)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, and edges with two equivalent Ti(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 49-50°. Both Ti(1)-O(12) bond lengths are 1.99 Å. Both Ti(1)-O(2) bond lengths are 2.05 Å. Both Ti(1)-O(6) bond lengths are 1.92 Å. In the second Ti site, Ti(2) is bonded to two equivalent O(12), two equivalent O(3), and two equivalent O(6) atoms to form TiO6 octahedra that share corners with two equivalent Ti(3)O6 octahedra, corners with two equivalent Ti(4)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra, and edges with two equivalent Ti(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 50-51°. Both Ti(2)-O(12) bond lengths are 1.94 Å. Both Ti(2)-O(3) bond lengths are 2.05 Å. Both Ti(2)-O(6) bond lengths are 2.00 Å. In the third Ti site, Ti(3) is bonded to one O(6), one O(9), two equivalent O(11), and two equivalent O(13) atoms to form TiO6 octahedra that share  a cornercorner with one Ti(1)O6 octahedra,  a cornercorner with one Ti(2)O6 octahedra,  a cornercorner with one Si(3)O4 tetrahedra, and edges with two equivalent Ti(3)O6 octahedra. The corner-sharing octahedral tilt angles are 50°. The Ti(3)-O(6) bond length is 2.11 Å. The Ti(3)-O(9) bond length is 2.04 Å. There is one shorter (1.83 Å) and one longer (2.09 Å) Ti(3)-O(11) bond length. There is one shorter (1.84 Å) and one longer (2.13 Å) Ti(3)-O(13) bond length. In the fourth Ti site, Ti(4) is bonded to one O(12), one O(7), two equivalent O(4), and two equivalent O(5) atoms to form TiO6 octahedra that share  a cornercorner with one Ti(1)O6 octahedra,  a cornercorner with one Ti(2)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, and edges with two equivalent Ti(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 49-51°. The Ti(4)-O(12) bond length is 2.09 Å. The Ti(4)-O(7) bond length is 2.03 Å. There is one shorter (1.84 Å) and one longer (2.10 Å) Ti(4)-O(4) bond length. There is one shorter (1.83 Å) and one longer (2.10 Å) Ti(4)-O(5) bond length. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(3), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Ti(1)O6 octahedra,  a cornercorner with one Ti(2)O6 octahedra,  a cornercorner with one Si(2)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles are 54°. The Si(1)-O(1) bond length is 1.64 Å. The Si(1)-O(2) bond length is 1.63 Å. The Si(1)-O(3) bond length is 1.63 Å. The Si(1)-O(8) bond length is 1.65 Å. In the second Si site, Si(2) is bonded to two equivalent O(1) and two equivalent O(7) atoms to form SiO4 tetrahedra that share corners with two equivalent Ti(4)O6 octahedra and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 56°. Both Si(2)-O(1) bond lengths are 1.65 Å. Both Si(2)-O(7) bond lengths are 1.62 Å. In the third Si site, Si(3) is bonded to two equivalent O(8) and two equivalent O(9) atoms to form SiO4 tetrahedra that share corners with two equivalent Ti(3)O6 octahedra and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 56°. Both Si(3)-O(8) bond lengths are 1.65 Å. Both Si(3)-O(9) bond lengths are 1.62 Å. There are thirteen inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to two equivalent Ba(1), one Si(1), and one Si(2) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Ba(1), one Ba(2), one Ti(1), and one Si(1) atom. In the third O site, O(3) is bonded in a distorted bent 120 degrees geometry to one Ba(1), one Ba(2), one Ti(2), and one Si(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to two equivalent Ba(1) and two equivalent Ti(4) atoms. In the fifth O site, O(5) is bonded in a distorted T-shaped geometry to one Ba(1) and two equivalent Ti(4) atoms. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Ba(2), one Ti(1), one Ti(2), and one Ti(3) atom. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to two equivalent Ba(1), one Ti(4), and one Si(2) atom. In the eighth O site, O(8) is bonded in a distorted bent 150 degrees geometry to two equivalent Ba(2), one Si(1), and one Si(3) atom. In the ninth O site, O(9) is bonded in a 4-coordinate geometry to two equivalent Ba(2), one Ti(3), and one Si(3) atom. In the tenth O site, O(10) is bonded in a rectangular see-saw-like geometry to two equivalent Ba(1) and two equivalent Ba(2) atoms. In the eleventh O site, O(11) is bonded in a distorted T-shaped geometry to one Ba(2) and two equivalent Ti(3) atoms. In the twelfth O site, O(12) is bonded in a distorted trigonal planar geometry to one Ba(1), one Ti(1), one Ti(2), and one Ti(4) atom. In the thirteenth O site, O(13) is bonded in a 4-coordinate geometry to two equivalent Ba(2) and two equivalent Ti(3) atoms.