Nd2Ti2O7 crystallizes in the monoclinic P2_1 space group. There are four inequivalent Nd sites. In the first Nd site, Nd(1) is bonded in a 9-coordinate geometry to one O(3), one O(4), one O(5), one O(6), one O(9), two equivalent O(1), and two equivalent O(2) atoms. In the second Nd site, Nd(2) is bonded in a 8-coordinate geometry to one O(1), one O(10), one O(2), one O(4), one O(5), one O(6), one O(7), and one O(8) atom. In the third Nd site, Nd(3) is bonded in a 7-coordinate geometry to one O(11), one O(14), one O(9), two equivalent O(12), and two equivalent O(13) atoms. In the fourth Nd site, Nd(4) is bonded in a 8-coordinate geometry to one O(10), one O(11), one O(12), one O(13), one O(7), one O(8), and two equivalent O(14) atoms. There are four inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(3), one O(4), one O(5), one O(7), and two equivalent O(2) atoms to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 19-44°. In the second Ti site, Ti(2) is bonded to one O(3), one O(4), one O(6), one O(8), and two equivalent O(1) atoms to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 19-39°. In the third Ti site, Ti(3) is bonded to one O(10), one O(11), one O(14), one O(5), one O(7), and one O(9) atom to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 24-44°. In the fourth Ti site, Ti(4) is bonded to one O(10), one O(12), one O(13), one O(6), one O(8), and one O(9) atom to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 24-39°. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Nd(2), two equivalent Nd(1), and two equivalent Ti(2) atoms. In the second O site, O(2) is bonded in a 5-coordinate geometry to one Nd(2), two equivalent Nd(1), and two equivalent Ti(1) atoms. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Nd(1), one Ti(1), and one Ti(2) atom. In the fourth O site, O(4) is bonded to one Nd(1), one Nd(2), one Ti(1), and one Ti(2) atom to form a mixture of distorted corner and edge-sharing ONd2Ti2 tetrahedra. In the fifth O site, O(5) is bonded to one Nd(1), one Nd(2), one Ti(1), and one Ti(3) atom to form distorted ONd2Ti2 tetrahedra that share  a cornercorner with one O(4)Nd2Ti2 tetrahedra,  a cornercorner with one O(14)Nd3Ti tetrahedra, corners with two equivalent O(6)Nd2Ti2 tetrahedra, and  an edgeedge with one O(4)Nd2Ti2 tetrahedra. In the sixth O site, O(6) is bonded to one Nd(1), one Nd(2), one Ti(2), and one Ti(4) atom to form distorted ONd2Ti2 tetrahedra that share  a cornercorner with one O(4)Nd2Ti2 tetrahedra,  a cornercorner with one O(12)Nd3Ti tetrahedra,  a cornercorner with one O(13)Nd3Ti tetrahedra, corners with two equivalent O(5)Nd2Ti2 tetrahedra, and  an edgeedge with one O(4)Nd2Ti2 tetrahedra. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Nd(2), one Nd(4), one Ti(1), and one Ti(3) atom. In the eighth O site, O(8) is bonded in a 4-coordinate geometry to one Nd(2), one Nd(4), one Ti(2), and one Ti(4) atom. In the ninth O site, O(9) is bonded in a 4-coordinate geometry to one Nd(1), one Nd(3), one Ti(3), and one Ti(4) atom. In the tenth O site, O(10) is bonded in a 4-coordinate geometry to one Nd(2), one Nd(4), one Ti(3), and one Ti(4) atom. In the eleventh O site, O(11) is bonded in a 3-coordinate geometry to one Nd(3), one Nd(4), and one Ti(3) atom. In the twelfth O site, O(12) is bonded to one Nd(4), two equivalent Nd(3), and one Ti(4) atom to form distorted ONd3Ti tetrahedra that share  a cornercorner with one O(6)Nd2Ti2 tetrahedra, corners with two equivalent O(12)Nd3Ti tetrahedra, corners with four equivalent O(14)Nd3Ti tetrahedra, and edges with three equivalent O(13)Nd3Ti tetrahedra. In the thirteenth O site, O(13) is bonded to one Nd(4), two equivalent Nd(3), and one Ti(4) atom to form distorted ONd3Ti tetrahedra that share  a cornercorner with one O(6)Nd2Ti2 tetrahedra, corners with two equivalent O(13)Nd3Ti tetrahedra, corners with two equivalent O(14)Nd3Ti tetrahedra,  an edgeedge with one O(14)Nd3Ti tetrahedra, and edges with three equivalent O(12)Nd3Ti tetrahedra. In the fourteenth O site, O(14) is bonded to one Nd(3), two equivalent Nd(4), and one Ti(3) atom to form distorted ONd3Ti tetrahedra that share  a cornercorner with one O(5)Nd2Ti2 tetrahedra, corners with two equivalent O(13)Nd3Ti tetrahedra, corners with two equivalent O(14)Nd3Ti tetrahedra, corners with four equivalent O(12)Nd3Ti tetrahedra, and  an edgeedge with one O(13)Nd3Ti tetrahedra.
Nd2Ti2O7 crystallizes in the monoclinic P2_1 space group. There are four inequivalent Nd sites. In the first Nd site, Nd(1) is bonded in a 9-coordinate geometry to one O(3), one O(4), one O(5), one O(6), one O(9), two equivalent O(1), and two equivalent O(2) atoms. The Nd(1)-O(3) bond length is 2.44 Å. The Nd(1)-O(4) bond length is 2.40 Å. The Nd(1)-O(5) bond length is 2.33 Å. The Nd(1)-O(6) bond length is 2.36 Å. The Nd(1)-O(9) bond length is 2.80 Å. There is one shorter (2.61 Å) and one longer (2.74 Å) Nd(1)-O(1) bond length. There is one shorter (2.60 Å) and one longer (2.71 Å) Nd(1)-O(2) bond length. In the second Nd site, Nd(2) is bonded in a 8-coordinate geometry to one O(1), one O(10), one O(2), one O(4), one O(5), one O(6), one O(7), and one O(8) atom. The Nd(2)-O(1) bond length is 2.43 Å. The Nd(2)-O(10) bond length is 2.46 Å. The Nd(2)-O(2) bond length is 2.41 Å. The Nd(2)-O(4) bond length is 2.36 Å. The Nd(2)-O(5) bond length is 2.46 Å. The Nd(2)-O(6) bond length is 2.51 Å. The Nd(2)-O(7) bond length is 2.58 Å. The Nd(2)-O(8) bond length is 2.56 Å. In the third Nd site, Nd(3) is bonded in a 7-coordinate geometry to one O(11), one O(14), one O(9), two equivalent O(12), and two equivalent O(13) atoms. The Nd(3)-O(11) bond length is 2.32 Å. The Nd(3)-O(14) bond length is 2.42 Å. The Nd(3)-O(9) bond length is 2.46 Å. There is one shorter (2.42 Å) and one longer (2.43 Å) Nd(3)-O(12) bond length. Both Nd(3)-O(13) bond lengths are 2.42 Å. In the fourth Nd site, Nd(4) is bonded in a 8-coordinate geometry to one O(10), one O(11), one O(12), one O(13), one O(7), one O(8), and two equivalent O(14) atoms. The Nd(4)-O(10) bond length is 2.58 Å. The Nd(4)-O(11) bond length is 2.39 Å. The Nd(4)-O(12) bond length is 2.44 Å. The Nd(4)-O(13) bond length is 2.50 Å. The Nd(4)-O(7) bond length is 2.60 Å. The Nd(4)-O(8) bond length is 2.69 Å. There is one shorter (2.50 Å) and one longer (2.52 Å) Nd(4)-O(14) bond length. There are four inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(3), one O(4), one O(5), one O(7), and two equivalent O(2) atoms to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 19-44°. The Ti(1)-O(3) bond length is 1.97 Å. The Ti(1)-O(4) bond length is 2.00 Å. The Ti(1)-O(5) bond length is 1.92 Å. The Ti(1)-O(7) bond length is 1.83 Å. There is one shorter (1.96 Å) and one longer (2.28 Å) Ti(1)-O(2) bond length. In the second Ti site, Ti(2) is bonded to one O(3), one O(4), one O(6), one O(8), and two equivalent O(1) atoms to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 19-39°. The Ti(2)-O(3) bond length is 1.96 Å. The Ti(2)-O(4) bond length is 2.00 Å. The Ti(2)-O(6) bond length is 1.93 Å. The Ti(2)-O(8) bond length is 1.83 Å. There is one shorter (1.95 Å) and one longer (2.23 Å) Ti(2)-O(1) bond length. In the third Ti site, Ti(3) is bonded to one O(10), one O(11), one O(14), one O(5), one O(7), and one O(9) atom to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 24-44°. The Ti(3)-O(10) bond length is 1.99 Å. The Ti(3)-O(11) bond length is 1.77 Å. The Ti(3)-O(14) bond length is 1.90 Å. The Ti(3)-O(5) bond length is 2.04 Å. The Ti(3)-O(7) bond length is 2.28 Å. The Ti(3)-O(9) bond length is 1.98 Å. In the fourth Ti site, Ti(4) is bonded to one O(10), one O(12), one O(13), one O(6), one O(8), and one O(9) atom to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 24-39°. The Ti(4)-O(10) bond length is 2.01 Å. The Ti(4)-O(12) bond length is 1.86 Å. The Ti(4)-O(13) bond length is 1.85 Å. The Ti(4)-O(6) bond length is 1.99 Å. The Ti(4)-O(8) bond length is 2.22 Å. The Ti(4)-O(9) bond length is 1.95 Å. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Nd(2), two equivalent Nd(1), and two equivalent Ti(2) atoms. In the second O site, O(2) is bonded in a 5-coordinate geometry to one Nd(2), two equivalent Nd(1), and two equivalent Ti(1) atoms. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Nd(1), one Ti(1), and one Ti(2) atom. In the fourth O site, O(4) is bonded to one Nd(1), one Nd(2), one Ti(1), and one Ti(2) atom to form a mixture of distorted corner and edge-sharing ONd2Ti2 tetrahedra. In the fifth O site, O(5) is bonded to one Nd(1), one Nd(2), one Ti(1), and one Ti(3) atom to form distorted ONd2Ti2 tetrahedra that share  a cornercorner with one O(4)Nd2Ti2 tetrahedra,  a cornercorner with one O(14)Nd3Ti tetrahedra, corners with two equivalent O(6)Nd2Ti2 tetrahedra, and  an edgeedge with one O(4)Nd2Ti2 tetrahedra. In the sixth O site, O(6) is bonded to one Nd(1), one Nd(2), one Ti(2), and one Ti(4) atom to form distorted ONd2Ti2 tetrahedra that share  a cornercorner with one O(4)Nd2Ti2 tetrahedra,  a cornercorner with one O(12)Nd3Ti tetrahedra,  a cornercorner with one O(13)Nd3Ti tetrahedra, corners with two equivalent O(5)Nd2Ti2 tetrahedra, and  an edgeedge with one O(4)Nd2Ti2 tetrahedra. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Nd(2), one Nd(4), one Ti(1), and one Ti(3) atom. In the eighth O site, O(8) is bonded in a 4-coordinate geometry to one Nd(2), one Nd(4), one Ti(2), and one Ti(4) atom. In the ninth O site, O(9) is bonded in a 4-coordinate geometry to one Nd(1), one Nd(3), one Ti(3), and one Ti(4) atom. In the tenth O site, O(10) is bonded in a 4-coordinate geometry to one Nd(2), one Nd(4), one Ti(3), and one Ti(4) atom. In the eleventh O site, O(11) is bonded in a 3-coordinate geometry to one Nd(3), one Nd(4), and one Ti(3) atom. In the twelfth O site, O(12) is bonded to one Nd(4), two equivalent Nd(3), and one Ti(4) atom to form distorted ONd3Ti tetrahedra that share  a cornercorner with one O(6)Nd2Ti2 tetrahedra, corners with two equivalent O(12)Nd3Ti tetrahedra, corners with four equivalent O(14)Nd3Ti tetrahedra, and edges with three equivalent O(13)Nd3Ti tetrahedra. In the thirteenth O site, O(13) is bonded to one Nd(4), two equivalent Nd(3), and one Ti(4) atom to form distorted ONd3Ti tetrahedra that share  a cornercorner with one O(6)Nd2Ti2 tetrahedra, corners with two equivalent O(13)Nd3Ti tetrahedra, corners with two equivalent O(14)Nd3Ti tetrahedra,  an edgeedge with one O(14)Nd3Ti tetrahedra, and edges with three equivalent O(12)Nd3Ti tetrahedra. In the fourteenth O site, O(14) is bonded to one Nd(3), two equivalent Nd(4), and one Ti(3) atom to form distorted ONd3Ti tetrahedra that share  a cornercorner with one O(5)Nd2Ti2 tetrahedra, corners with two equivalent O(13)Nd3Ti tetrahedra, corners with two equivalent O(14)Nd3Ti tetrahedra, corners with four equivalent O(12)Nd3Ti tetrahedra, and  an edgeedge with one O(13)Nd3Ti tetrahedra.