Sr4Nb2O9 is Pb (Zr_0.50 Ti_0.48) O_3-like structured and crystallizes in the triclinic P1 space group. There are eight inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 10-coordinate geometry to one O(15), one O(16), one O(18), one O(3), one O(5), one O(6), two equivalent O(1), and two equivalent O(2) atoms. In the second Sr site, Sr(2) is bonded in a 6-coordinate geometry to one O(1), one O(12), one O(2), one O(3), one O(5), and one O(6) atom. In the third Sr site, Sr(3) is bonded in a 5-coordinate geometry to one O(12), one O(13), one O(4), one O(7), and one O(8) atom. In the fourth Sr site, Sr(4) is bonded in a 8-coordinate geometry to one O(1), one O(12), one O(2), one O(3), one O(4), one O(5), one O(6), and one O(7) atom. In the fifth Sr site, Sr(5) is bonded in a 12-coordinate geometry to one O(11), one O(13), one O(15), one O(16), one O(18), one O(9), two equivalent O(10), two equivalent O(14), and two equivalent O(17) atoms. In the sixth Sr site, Sr(6) is bonded to one O(11), one O(12), one O(13), one O(4), one O(7), one O(8), and one O(9) atom to form distorted SrO7 pentagonal bipyramids that share corners with three equivalent Nb(3)O6 octahedra, corners with two equivalent Nb(2)O6 pentagonal pyramids, and  an edgeedge with one Nb(2)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 17-33°. In the seventh Sr site, Sr(7) is bonded in a 8-coordinate geometry to one O(10), one O(11), one O(13), one O(14), one O(17), one O(8), and two equivalent O(9) atoms. In the eighth Sr site, Sr(8) is bonded in a 8-coordinate geometry to one O(1), one O(14), one O(15), one O(16), one O(17), one O(18), one O(2), and one O(6) atom. There are four inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(15), one O(16), one O(18), one O(2), and one O(6) atom to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 16-17°. In the second Nb site, Nb(2) is bonded to one O(12), one O(3), one O(4), one O(5), one O(7), and one O(8) atom to form distorted NbO6 pentagonal pyramids that share corners with two equivalent Sr(6)O7 pentagonal bipyramids and  an edgeedge with one Sr(6)O7 pentagonal bipyramid. In the third Nb site, Nb(3) is bonded to one O(10), one O(11), one O(13), one O(14), one O(17), and one O(9) atom to form NbO6 octahedra that share corners with three equivalent Nb(4)O6 octahedra and corners with three equivalent Sr(6)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 13-18°. In the fourth Nb site, Nb(4) is bonded to one O(10), one O(14), one O(15), one O(16), one O(17), and one O(18) atom to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 13-18°. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded in a 1-coordinate geometry to one Sr(2), one Sr(4), one Sr(8), two equivalent Sr(1), and one Nb(1) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one Sr(2), one Sr(4), one Sr(8), two equivalent Sr(1), and one Nb(1) atom. In the third O site, O(3) is bonded to one Sr(1), one Sr(2), one Sr(4), and one Nb(2) atom to form a mixture of distorted corner and edge-sharing OSr3Nb trigonal pyramids. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Sr(3), one Sr(4), one Sr(6), and one Nb(2) atom. In the fifth O site, O(5) is bonded to one Sr(1), one Sr(2), one Sr(4), and one Nb(2) atom to form a mixture of corner and edge-sharing OSr3Nb tetrahedra. In the sixth O site, O(6) is bonded in a 1-coordinate geometry to one Sr(1), one Sr(2), one Sr(4), one Sr(8), and one Nb(1) atom. In the seventh O site, O(7) is bonded to one Sr(3), one Sr(4), one Sr(6), and one Nb(2) atom to form a mixture of distorted corner and edge-sharing OSr3Nb trigonal pyramids. In the eighth O site, O(8) is bonded to one Sr(3), one Sr(6), one Sr(7), and one Nb(2) atom to form a mixture of distorted corner and edge-sharing OSr3Nb trigonal pyramids. In the ninth O site, O(9) is bonded in a 1-coordinate geometry to one Sr(5), one Sr(6), two equivalent Sr(7), and one Nb(3) atom. In the tenth O site, O(10) is bonded in a 4-coordinate geometry to one Sr(7), two equivalent Sr(5), one Nb(3), and one Nb(4) atom. In the eleventh O site, O(11) is bonded in a 4-coordinate geometry to one Sr(5), one Sr(6), one Sr(7), and one Nb(3) atom. In the twelfth O site, O(12) is bonded in a 5-coordinate geometry to one Sr(2), one Sr(3), one Sr(4), one Sr(6), and one Nb(2) atom. In the thirteenth O site, O(13) is bonded in a 1-coordinate geometry to one Sr(3), one Sr(5), one Sr(6), one Sr(7), and one Nb(3) atom. In the fourteenth O site, O(14) is bonded in a 2-coordinate geometry to one Sr(7), one Sr(8), two equivalent Sr(5), one Nb(3), and one Nb(4) atom. In the fifteenth O site, O(15) is bonded in a 2-coordinate geometry to one Sr(1), one Sr(5), one Sr(8), one Nb(1), and one Nb(4) atom. In the sixteenth O site, O(16) is bonded in a 2-coordinate geometry to one Sr(1), one Sr(5), one Sr(8), one Nb(1), and one Nb(4) atom. In the seventeenth O site, O(17) is bonded in a 5-coordinate geometry to one Sr(7), one Sr(8), two equivalent Sr(5), one Nb(3), and one Nb(4) atom. In the eighteenth O site, O(18) is bonded in a 2-coordinate geometry to one Sr(1), one Sr(5), one Sr(8), one Nb(1), and one Nb(4) atom.
Sr4Nb2O9 is Pb (Zr_0.50 Ti_0.48) O_3-like structured and crystallizes in the triclinic P1 space group. There are eight inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 10-coordinate geometry to one O(15), one O(16), one O(18), one O(3), one O(5), one O(6), two equivalent O(1), and two equivalent O(2) atoms. The Sr(1)-O(15) bond length is 3.10 Å. The Sr(1)-O(16) bond length is 2.99 Å. The Sr(1)-O(18) bond length is 2.94 Å. The Sr(1)-O(3) bond length is 2.39 Å. The Sr(1)-O(5) bond length is 2.52 Å. The Sr(1)-O(6) bond length is 2.58 Å. There is one shorter (2.67 Å) and one longer (3.22 Å) Sr(1)-O(1) bond length. There is one shorter (2.81 Å) and one longer (3.16 Å) Sr(1)-O(2) bond length. In the second Sr site, Sr(2) is bonded in a 6-coordinate geometry to one O(1), one O(12), one O(2), one O(3), one O(5), and one O(6) atom. The Sr(2)-O(1) bond length is 2.53 Å. The Sr(2)-O(12) bond length is 2.52 Å. The Sr(2)-O(2) bond length is 2.77 Å. The Sr(2)-O(3) bond length is 2.60 Å. The Sr(2)-O(5) bond length is 2.32 Å. The Sr(2)-O(6) bond length is 2.52 Å. In the third Sr site, Sr(3) is bonded in a 5-coordinate geometry to one O(12), one O(13), one O(4), one O(7), and one O(8) atom. The Sr(3)-O(12) bond length is 2.47 Å. The Sr(3)-O(13) bond length is 2.60 Å. The Sr(3)-O(4) bond length is 2.44 Å. The Sr(3)-O(7) bond length is 2.47 Å. The Sr(3)-O(8) bond length is 2.50 Å. In the fourth Sr site, Sr(4) is bonded in a 8-coordinate geometry to one O(1), one O(12), one O(2), one O(3), one O(4), one O(5), one O(6), and one O(7) atom. The Sr(4)-O(1) bond length is 2.87 Å. The Sr(4)-O(12) bond length is 2.57 Å. The Sr(4)-O(2) bond length is 3.03 Å. The Sr(4)-O(3) bond length is 2.31 Å. The Sr(4)-O(4) bond length is 2.85 Å. The Sr(4)-O(5) bond length is 2.35 Å. The Sr(4)-O(6) bond length is 3.11 Å. The Sr(4)-O(7) bond length is 2.44 Å. In the fifth Sr site, Sr(5) is bonded in a 12-coordinate geometry to one O(11), one O(13), one O(15), one O(16), one O(18), one O(9), two equivalent O(10), two equivalent O(14), and two equivalent O(17) atoms. The Sr(5)-O(11) bond length is 2.64 Å. The Sr(5)-O(13) bond length is 2.98 Å. The Sr(5)-O(15) bond length is 2.83 Å. The Sr(5)-O(16) bond length is 3.08 Å. The Sr(5)-O(18) bond length is 2.98 Å. The Sr(5)-O(9) bond length is 2.75 Å. There is one shorter (2.68 Å) and one longer (3.21 Å) Sr(5)-O(10) bond length. There is one shorter (2.73 Å) and one longer (3.22 Å) Sr(5)-O(14) bond length. There is one shorter (2.68 Å) and one longer (3.22 Å) Sr(5)-O(17) bond length. In the sixth Sr site, Sr(6) is bonded to one O(11), one O(12), one O(13), one O(4), one O(7), one O(8), and one O(9) atom to form distorted SrO7 pentagonal bipyramids that share corners with three equivalent Nb(3)O6 octahedra, corners with two equivalent Nb(2)O6 pentagonal pyramids, and  an edgeedge with one Nb(2)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 17-33°. The Sr(6)-O(11) bond length is 2.53 Å. The Sr(6)-O(12) bond length is 2.74 Å. The Sr(6)-O(13) bond length is 2.82 Å. The Sr(6)-O(4) bond length is 2.60 Å. The Sr(6)-O(7) bond length is 2.47 Å. The Sr(6)-O(8) bond length is 2.41 Å. The Sr(6)-O(9) bond length is 2.56 Å. In the seventh Sr site, Sr(7) is bonded in a 8-coordinate geometry to one O(10), one O(11), one O(13), one O(14), one O(17), one O(8), and two equivalent O(9) atoms. The Sr(7)-O(10) bond length is 2.76 Å. The Sr(7)-O(11) bond length is 2.57 Å. The Sr(7)-O(13) bond length is 2.59 Å. The Sr(7)-O(14) bond length is 2.85 Å. The Sr(7)-O(17) bond length is 2.84 Å. The Sr(7)-O(8) bond length is 2.35 Å. There is one shorter (2.81 Å) and one longer (3.13 Å) Sr(7)-O(9) bond length. In the eighth Sr site, Sr(8) is bonded in a 8-coordinate geometry to one O(1), one O(14), one O(15), one O(16), one O(17), one O(18), one O(2), and one O(6) atom. The Sr(8)-O(1) bond length is 2.77 Å. The Sr(8)-O(14) bond length is 3.00 Å. The Sr(8)-O(15) bond length is 2.70 Å. The Sr(8)-O(16) bond length is 2.67 Å. The Sr(8)-O(17) bond length is 2.94 Å. The Sr(8)-O(18) bond length is 2.69 Å. The Sr(8)-O(2) bond length is 2.62 Å. The Sr(8)-O(6) bond length is 2.72 Å. There are four inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(15), one O(16), one O(18), one O(2), and one O(6) atom to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 16-17°. The Nb(1)-O(1) bond length is 1.94 Å. The Nb(1)-O(15) bond length is 2.20 Å. The Nb(1)-O(16) bond length is 2.18 Å. The Nb(1)-O(18) bond length is 2.23 Å. The Nb(1)-O(2) bond length is 1.88 Å. The Nb(1)-O(6) bond length is 1.90 Å. In the second Nb site, Nb(2) is bonded to one O(12), one O(3), one O(4), one O(5), one O(7), and one O(8) atom to form distorted NbO6 pentagonal pyramids that share corners with two equivalent Sr(6)O7 pentagonal bipyramids and  an edgeedge with one Sr(6)O7 pentagonal bipyramid. The Nb(2)-O(12) bond length is 2.02 Å. The Nb(2)-O(3) bond length is 2.03 Å. The Nb(2)-O(4) bond length is 2.01 Å. The Nb(2)-O(5) bond length is 2.09 Å. The Nb(2)-O(7) bond length is 2.00 Å. The Nb(2)-O(8) bond length is 2.08 Å. In the third Nb site, Nb(3) is bonded to one O(10), one O(11), one O(13), one O(14), one O(17), and one O(9) atom to form NbO6 octahedra that share corners with three equivalent Nb(4)O6 octahedra and corners with three equivalent Sr(6)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 13-18°. The Nb(3)-O(10) bond length is 2.18 Å. The Nb(3)-O(11) bond length is 1.94 Å. The Nb(3)-O(13) bond length is 1.92 Å. The Nb(3)-O(14) bond length is 2.17 Å. The Nb(3)-O(17) bond length is 2.21 Å. The Nb(3)-O(9) bond length is 1.90 Å. In the fourth Nb site, Nb(4) is bonded to one O(10), one O(14), one O(15), one O(16), one O(17), and one O(18) atom to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 13-18°. The Nb(4)-O(10) bond length is 2.07 Å. The Nb(4)-O(14) bond length is 2.05 Å. The Nb(4)-O(15) bond length is 2.03 Å. The Nb(4)-O(16) bond length is 2.00 Å. The Nb(4)-O(17) bond length is 2.04 Å. The Nb(4)-O(18) bond length is 2.02 Å. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded in a 1-coordinate geometry to one Sr(2), one Sr(4), one Sr(8), two equivalent Sr(1), and one Nb(1) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to one Sr(2), one Sr(4), one Sr(8), two equivalent Sr(1), and one Nb(1) atom. In the third O site, O(3) is bonded to one Sr(1), one Sr(2), one Sr(4), and one Nb(2) atom to form a mixture of distorted corner and edge-sharing OSr3Nb trigonal pyramids. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Sr(3), one Sr(4), one Sr(6), and one Nb(2) atom. In the fifth O site, O(5) is bonded to one Sr(1), one Sr(2), one Sr(4), and one Nb(2) atom to form a mixture of corner and edge-sharing OSr3Nb tetrahedra. In the sixth O site, O(6) is bonded in a 1-coordinate geometry to one Sr(1), one Sr(2), one Sr(4), one Sr(8), and one Nb(1) atom. In the seventh O site, O(7) is bonded to one Sr(3), one Sr(4), one Sr(6), and one Nb(2) atom to form a mixture of distorted corner and edge-sharing OSr3Nb trigonal pyramids. In the eighth O site, O(8) is bonded to one Sr(3), one Sr(6), one Sr(7), and one Nb(2) atom to form a mixture of distorted corner and edge-sharing OSr3Nb trigonal pyramids. In the ninth O site, O(9) is bonded in a 1-coordinate geometry to one Sr(5), one Sr(6), two equivalent Sr(7), and one Nb(3) atom. In the tenth O site, O(10) is bonded in a 4-coordinate geometry to one Sr(7), two equivalent Sr(5), one Nb(3), and one Nb(4) atom. In the eleventh O site, O(11) is bonded in a 4-coordinate geometry to one Sr(5), one Sr(6), one Sr(7), and one Nb(3) atom. In the twelfth O site, O(12) is bonded in a 5-coordinate geometry to one Sr(2), one Sr(3), one Sr(4), one Sr(6), and one Nb(2) atom. In the thirteenth O site, O(13) is bonded in a 1-coordinate geometry to one Sr(3), one Sr(5), one Sr(6), one Sr(7), and one Nb(3) atom. In the fourteenth O site, O(14) is bonded in a 2-coordinate geometry to one Sr(7), one Sr(8), two equivalent Sr(5), one Nb(3), and one Nb(4) atom. In the fifteenth O site, O(15) is bonded in a 2-coordinate geometry to one Sr(1), one Sr(5), one Sr(8), one Nb(1), and one Nb(4) atom. In the sixteenth O site, O(16) is bonded in a 2-coordinate geometry to one Sr(1), one Sr(5), one Sr(8), one Nb(1), and one Nb(4) atom. In the seventeenth O site, O(17) is bonded in a 5-coordinate geometry to one Sr(7), one Sr(8), two equivalent Sr(5), one Nb(3), and one Nb(4) atom. In the eighteenth O site, O(18) is bonded in a 2-coordinate geometry to one Sr(1), one Sr(5), one Sr(8), one Nb(1), and one Nb(4) atom.