Er10Ti6O27 crystallizes in the monoclinic Cm space group. There are seven inequivalent Er sites. In the first Er site, Er(1) is bonded to one O(1), one O(11), one O(12), one O(15), one O(17), one O(7), and one O(9) atom to form distorted ErO7 pentagonal bipyramids that share  a cornercorner with one Er(7)O6 octahedra,  a cornercorner with one Er(1)O7 pentagonal bipyramid, and  an edgeedge with one Er(1)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles are 71°. In the second Er site, Er(2) is bonded in a 6-coordinate geometry to one O(1), one O(10), one O(2), one O(3), one O(4), and one O(7) atom. In the third Er site, Er(3) is bonded in a 7-coordinate geometry to one O(11), one O(13), one O(17), one O(18), one O(19), one O(5), and one O(8) atom. In the fourth Er site, Er(4) is bonded in a 7-coordinate geometry to one O(3), one O(6), one O(9), two equivalent O(4), and two equivalent O(7) atoms. In the fifth Er site, Er(5) is bonded in a 3-coordinate geometry to one O(14), two equivalent O(10), and two equivalent O(5) atoms. In the sixth Er site, Er(6) is bonded in a 7-coordinate geometry to one O(12), one O(14), one O(18), two equivalent O(11), and two equivalent O(13) atoms. In the seventh Er site, Er(7) is bonded to one O(19), one O(8), two equivalent O(11), and two equivalent O(13) atoms to form distorted corner-sharing ErO6 octahedra. There are five inequivalent Ti sites. In the first Ti site, Ti(1) is bonded in a 6-coordinate geometry to one O(15), one O(8), two equivalent O(1), and two equivalent O(17) atoms. In the second Ti site, Ti(2) is bonded in a 7-coordinate geometry to one O(10), one O(13), one O(14), one O(16), one O(4), one O(5), and one O(6) atom. In the third Ti site, Ti(3) is bonded in a 5-coordinate geometry to one O(16), one O(19), one O(2), and two equivalent O(10) atoms. In the fourth Ti site, Ti(4) is bonded in a 6-coordinate geometry to one O(12), one O(18), one O(3), one O(9), and two equivalent O(17) atoms. In the fifth Ti site, Ti(5) is bonded in a 7-coordinate geometry to one O(15), one O(16), one O(2), two equivalent O(4), and two equivalent O(7) atoms. There are nineteen inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Er(1), one Er(2), and one Ti(1) atom. In the second O site, O(2) is bonded to two equivalent Er(2), one Ti(3), and one Ti(5) atom to form OEr2Ti2 tetrahedra that share  a cornercorner with one O(15)Er2Ti2 tetrahedra,  a cornercorner with one O(19)Er3Ti tetrahedra,  an edgeedge with one O(3)Er3Ti tetrahedra, and  an edgeedge with one O(16)Ti4 trigonal pyramid. In the third O site, O(3) is bonded to one Er(4), two equivalent Er(2), and one Ti(4) atom to form OEr3Ti tetrahedra that share  a cornercorner with one O(18)Er3Ti tetrahedra, corners with two equivalent O(17)Er2Ti2 tetrahedra,  a cornercorner with one O(12)Er3Ti trigonal pyramid,  an edgeedge with one O(2)Er2Ti2 tetrahedra, and  an edgeedge with one O(9)Er3Ti tetrahedra. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Er(2), one Er(4), one Ti(2), and one Ti(5) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Er(3), one Er(5), and one Ti(2) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Er(4) and two equivalent Ti(2) atoms. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Er(1), one Er(2), one Er(4), and one Ti(5) atom. In the eighth O site, O(8) is bonded to one Er(7), two equivalent Er(3), and one Ti(1) atom to form OEr3Ti tetrahedra that share  a cornercorner with one O(15)Er2Ti2 tetrahedra, corners with two equivalent O(18)Er3Ti tetrahedra, corners with three equivalent O(19)Er3Ti tetrahedra, corners with four equivalent O(11)Er4 tetrahedra, and edges with two equivalent O(17)Er2Ti2 tetrahedra. In the ninth O site, O(9) is bonded to one Er(4), two equivalent Er(1), and one Ti(4) atom to form OEr3Ti tetrahedra that share  a cornercorner with one O(18)Er3Ti tetrahedra, corners with two equivalent O(15)Er2Ti2 tetrahedra, corners with two equivalent O(11)Er4 tetrahedra, corners with three equivalent O(12)Er3Ti trigonal pyramids,  an edgeedge with one O(3)Er3Ti tetrahedra, and edges with two equivalent O(17)Er2Ti2 tetrahedra. In the tenth O site, O(10) is bonded in a 4-coordinate geometry to one Er(2), one Er(5), one Ti(2), and one Ti(3) atom. In the eleventh O site, O(11) is bonded to one Er(1), one Er(3), one Er(6), and one Er(7) atom to form OEr4 tetrahedra that share  a cornercorner with one O(14)Er2Ti2 tetrahedra,  a cornercorner with one O(15)Er2Ti2 tetrahedra,  a cornercorner with one O(9)Er3Ti tetrahedra, corners with two equivalent O(18)Er3Ti tetrahedra, corners with two equivalent O(8)Er3Ti tetrahedra, corners with two equivalent O(11)Er4 tetrahedra,  an edgeedge with one O(17)Er2Ti2 tetrahedra,  an edgeedge with one O(19)Er3Ti tetrahedra, and  an edgeedge with one O(12)Er3Ti trigonal pyramid. In the twelfth O site, O(12) is bonded to one Er(6), two equivalent Er(1), and one Ti(4) atom to form distorted OEr3Ti trigonal pyramids that share  a cornercorner with one O(14)Er2Ti2 tetrahedra,  a cornercorner with one O(3)Er3Ti tetrahedra, corners with three equivalent O(9)Er3Ti tetrahedra, corners with four equivalent O(17)Er2Ti2 tetrahedra,  an edgeedge with one O(15)Er2Ti2 tetrahedra,  an edgeedge with one O(18)Er3Ti tetrahedra, and edges with two equivalent O(11)Er4 tetrahedra. In the thirteenth O site, O(13) is bonded in a 4-coordinate geometry to one Er(3), one Er(6), one Er(7), and one Ti(2) atom. In the fourteenth O site, O(14) is bonded to one Er(5), one Er(6), and two equivalent Ti(2) atoms to form OEr2Ti2 tetrahedra that share  a cornercorner with one O(18)Er3Ti tetrahedra, corners with two equivalent O(11)Er4 tetrahedra,  a cornercorner with one O(12)Er3Ti trigonal pyramid, and  an edgeedge with one O(16)Ti4 trigonal pyramid. In the fifteenth O site, O(15) is bonded to two equivalent Er(1), one Ti(1), and one Ti(5) atom to form OEr2Ti2 tetrahedra that share  a cornercorner with one O(2)Er2Ti2 tetrahedra,  a cornercorner with one O(8)Er3Ti tetrahedra, corners with two equivalent O(9)Er3Ti tetrahedra, corners with two equivalent O(11)Er4 tetrahedra,  a cornercorner with one O(16)Ti4 trigonal pyramid, edges with two equivalent O(17)Er2Ti2 tetrahedra, and  an edgeedge with one O(12)Er3Ti trigonal pyramid. In the sixteenth O site, O(16) is bonded to one Ti(3), one Ti(5), and two equivalent Ti(2) atoms to form OTi4 trigonal pyramids that share  a cornercorner with one O(15)Er2Ti2 tetrahedra,  a cornercorner with one O(19)Er3Ti tetrahedra,  an edgeedge with one O(14)Er2Ti2 tetrahedra, and  an edgeedge with one O(2)Er2Ti2 tetrahedra. In the seventeenth O site, O(17) is bonded to one Er(1), one Er(3), one Ti(1), and one Ti(4) atom to form distorted OEr2Ti2 tetrahedra that share  a cornercorner with one O(19)Er3Ti tetrahedra,  a cornercorner with one O(3)Er3Ti tetrahedra, corners with two equivalent O(17)Er2Ti2 tetrahedra, corners with two equivalent O(12)Er3Ti trigonal pyramids,  an edgeedge with one O(15)Er2Ti2 tetrahedra,  an edgeedge with one O(18)Er3Ti tetrahedra,  an edgeedge with one O(8)Er3Ti tetrahedra,  an edgeedge with one O(9)Er3Ti tetrahedra, and  an edgeedge with one O(11)Er4 tetrahedra. In the eighteenth O site, O(18) is bonded to one Er(6), two equivalent Er(3), and one Ti(4) atom to form OEr3Ti tetrahedra that share  a cornercorner with one O(14)Er2Ti2 tetrahedra,  a cornercorner with one O(3)Er3Ti tetrahedra,  a cornercorner with one O(9)Er3Ti tetrahedra, corners with two equivalent O(8)Er3Ti tetrahedra, corners with four equivalent O(11)Er4 tetrahedra,  an edgeedge with one O(19)Er3Ti tetrahedra, edges with two equivalent O(17)Er2Ti2 tetrahedra, and  an edgeedge with one O(12)Er3Ti trigonal pyramid. In the nineteenth O site, O(19) is bonded to one Er(7), two equivalent Er(3), and one Ti(3) atom to form distorted OEr3Ti tetrahedra that share  a cornercorner with one O(2)Er2Ti2 tetrahedra, corners with two equivalent O(17)Er2Ti2 tetrahedra, corners with three equivalent O(8)Er3Ti tetrahedra,  a cornercorner with one O(16)Ti4 trigonal pyramid,  an edgeedge with one O(18)Er3Ti tetrahedra, and edges with two equivalent O(11)Er4 tetrahedra.
Er10Ti6O27 crystallizes in the monoclinic Cm space group. There are seven inequivalent Er sites. In the first Er site, Er(1) is bonded to one O(1), one O(11), one O(12), one O(15), one O(17), one O(7), and one O(9) atom to form distorted ErO7 pentagonal bipyramids that share  a cornercorner with one Er(7)O6 octahedra,  a cornercorner with one Er(1)O7 pentagonal bipyramid, and  an edgeedge with one Er(1)O7 pentagonal bipyramid. The corner-sharing octahedral tilt angles are 71°. The Er(1)-O(1) bond length is 2.31 Å. The Er(1)-O(11) bond length is 2.28 Å. The Er(1)-O(12) bond length is 2.41 Å. The Er(1)-O(15) bond length is 2.38 Å. The Er(1)-O(17) bond length is 2.32 Å. The Er(1)-O(7) bond length is 2.41 Å. The Er(1)-O(9) bond length is 2.17 Å. In the second Er site, Er(2) is bonded in a 6-coordinate geometry to one O(1), one O(10), one O(2), one O(3), one O(4), and one O(7) atom. The Er(2)-O(1) bond length is 2.22 Å. The Er(2)-O(10) bond length is 2.36 Å. The Er(2)-O(2) bond length is 2.22 Å. The Er(2)-O(3) bond length is 2.17 Å. The Er(2)-O(4) bond length is 2.21 Å. The Er(2)-O(7) bond length is 2.13 Å. In the third Er site, Er(3) is bonded in a 7-coordinate geometry to one O(11), one O(13), one O(17), one O(18), one O(19), one O(5), and one O(8) atom. The Er(3)-O(11) bond length is 2.25 Å. The Er(3)-O(13) bond length is 2.40 Å. The Er(3)-O(17) bond length is 2.28 Å. The Er(3)-O(18) bond length is 2.15 Å. The Er(3)-O(19) bond length is 2.46 Å. The Er(3)-O(5) bond length is 2.26 Å. The Er(3)-O(8) bond length is 2.40 Å. In the fourth Er site, Er(4) is bonded in a 7-coordinate geometry to one O(3), one O(6), one O(9), two equivalent O(4), and two equivalent O(7) atoms. The Er(4)-O(3) bond length is 2.18 Å. The Er(4)-O(6) bond length is 2.26 Å. The Er(4)-O(9) bond length is 2.28 Å. Both Er(4)-O(4) bond lengths are 2.73 Å. Both Er(4)-O(7) bond lengths are 2.09 Å. In the fifth Er site, Er(5) is bonded in a 3-coordinate geometry to one O(14), two equivalent O(10), and two equivalent O(5) atoms. The Er(5)-O(14) bond length is 2.14 Å. Both Er(5)-O(10) bond lengths are 2.61 Å. Both Er(5)-O(5) bond lengths are 2.12 Å. In the sixth Er site, Er(6) is bonded in a 7-coordinate geometry to one O(12), one O(14), one O(18), two equivalent O(11), and two equivalent O(13) atoms. The Er(6)-O(12) bond length is 2.44 Å. The Er(6)-O(14) bond length is 2.31 Å. The Er(6)-O(18) bond length is 2.14 Å. Both Er(6)-O(11) bond lengths are 2.25 Å. Both Er(6)-O(13) bond lengths are 2.50 Å. In the seventh Er site, Er(7) is bonded to one O(19), one O(8), two equivalent O(11), and two equivalent O(13) atoms to form distorted corner-sharing ErO6 octahedra. The Er(7)-O(19) bond length is 2.18 Å. The Er(7)-O(8) bond length is 2.32 Å. Both Er(7)-O(11) bond lengths are 2.38 Å. Both Er(7)-O(13) bond lengths are 2.23 Å. There are five inequivalent Ti sites. In the first Ti site, Ti(1) is bonded in a 6-coordinate geometry to one O(15), one O(8), two equivalent O(1), and two equivalent O(17) atoms. The Ti(1)-O(15) bond length is 2.07 Å. The Ti(1)-O(8) bond length is 1.93 Å. Both Ti(1)-O(1) bond lengths are 1.87 Å. Both Ti(1)-O(17) bond lengths are 2.26 Å. In the second Ti site, Ti(2) is bonded in a 7-coordinate geometry to one O(10), one O(13), one O(14), one O(16), one O(4), one O(5), and one O(6) atom. The Ti(2)-O(10) bond length is 2.23 Å. The Ti(2)-O(13) bond length is 1.85 Å. The Ti(2)-O(14) bond length is 2.33 Å. The Ti(2)-O(16) bond length is 2.18 Å. The Ti(2)-O(4) bond length is 2.15 Å. The Ti(2)-O(5) bond length is 2.01 Å. The Ti(2)-O(6) bond length is 2.07 Å. In the third Ti site, Ti(3) is bonded in a 5-coordinate geometry to one O(16), one O(19), one O(2), and two equivalent O(10) atoms. The Ti(3)-O(16) bond length is 2.06 Å. The Ti(3)-O(19) bond length is 1.89 Å. The Ti(3)-O(2) bond length is 2.06 Å. Both Ti(3)-O(10) bond lengths are 1.89 Å. In the fourth Ti site, Ti(4) is bonded in a 6-coordinate geometry to one O(12), one O(18), one O(3), one O(9), and two equivalent O(17) atoms. The Ti(4)-O(12) bond length is 1.98 Å. The Ti(4)-O(18) bond length is 2.07 Å. The Ti(4)-O(3) bond length is 2.02 Å. The Ti(4)-O(9) bond length is 2.20 Å. Both Ti(4)-O(17) bond lengths are 1.93 Å. In the fifth Ti site, Ti(5) is bonded in a 7-coordinate geometry to one O(15), one O(16), one O(2), two equivalent O(4), and two equivalent O(7) atoms. The Ti(5)-O(15) bond length is 2.05 Å. The Ti(5)-O(16) bond length is 2.09 Å. The Ti(5)-O(2) bond length is 1.93 Å. Both Ti(5)-O(4) bond lengths are 1.89 Å. Both Ti(5)-O(7) bond lengths are 2.52 Å. There are nineteen inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Er(1), one Er(2), and one Ti(1) atom. In the second O site, O(2) is bonded to two equivalent Er(2), one Ti(3), and one Ti(5) atom to form OEr2Ti2 tetrahedra that share  a cornercorner with one O(15)Er2Ti2 tetrahedra,  a cornercorner with one O(19)Er3Ti tetrahedra,  an edgeedge with one O(3)Er3Ti tetrahedra, and  an edgeedge with one O(16)Ti4 trigonal pyramid. In the third O site, O(3) is bonded to one Er(4), two equivalent Er(2), and one Ti(4) atom to form OEr3Ti tetrahedra that share  a cornercorner with one O(18)Er3Ti tetrahedra, corners with two equivalent O(17)Er2Ti2 tetrahedra,  a cornercorner with one O(12)Er3Ti trigonal pyramid,  an edgeedge with one O(2)Er2Ti2 tetrahedra, and  an edgeedge with one O(9)Er3Ti tetrahedra. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Er(2), one Er(4), one Ti(2), and one Ti(5) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Er(3), one Er(5), and one Ti(2) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Er(4) and two equivalent Ti(2) atoms. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Er(1), one Er(2), one Er(4), and one Ti(5) atom. In the eighth O site, O(8) is bonded to one Er(7), two equivalent Er(3), and one Ti(1) atom to form OEr3Ti tetrahedra that share  a cornercorner with one O(15)Er2Ti2 tetrahedra, corners with two equivalent O(18)Er3Ti tetrahedra, corners with three equivalent O(19)Er3Ti tetrahedra, corners with four equivalent O(11)Er4 tetrahedra, and edges with two equivalent O(17)Er2Ti2 tetrahedra. In the ninth O site, O(9) is bonded to one Er(4), two equivalent Er(1), and one Ti(4) atom to form OEr3Ti tetrahedra that share  a cornercorner with one O(18)Er3Ti tetrahedra, corners with two equivalent O(15)Er2Ti2 tetrahedra, corners with two equivalent O(11)Er4 tetrahedra, corners with three equivalent O(12)Er3Ti trigonal pyramids,  an edgeedge with one O(3)Er3Ti tetrahedra, and edges with two equivalent O(17)Er2Ti2 tetrahedra. In the tenth O site, O(10) is bonded in a 4-coordinate geometry to one Er(2), one Er(5), one Ti(2), and one Ti(3) atom. In the eleventh O site, O(11) is bonded to one Er(1), one Er(3), one Er(6), and one Er(7) atom to form OEr4 tetrahedra that share  a cornercorner with one O(14)Er2Ti2 tetrahedra,  a cornercorner with one O(15)Er2Ti2 tetrahedra,  a cornercorner with one O(9)Er3Ti tetrahedra, corners with two equivalent O(18)Er3Ti tetrahedra, corners with two equivalent O(8)Er3Ti tetrahedra, corners with two equivalent O(11)Er4 tetrahedra,  an edgeedge with one O(17)Er2Ti2 tetrahedra,  an edgeedge with one O(19)Er3Ti tetrahedra, and  an edgeedge with one O(12)Er3Ti trigonal pyramid. In the twelfth O site, O(12) is bonded to one Er(6), two equivalent Er(1), and one Ti(4) atom to form distorted OEr3Ti trigonal pyramids that share  a cornercorner with one O(14)Er2Ti2 tetrahedra,  a cornercorner with one O(3)Er3Ti tetrahedra, corners with three equivalent O(9)Er3Ti tetrahedra, corners with four equivalent O(17)Er2Ti2 tetrahedra,  an edgeedge with one O(15)Er2Ti2 tetrahedra,  an edgeedge with one O(18)Er3Ti tetrahedra, and edges with two equivalent O(11)Er4 tetrahedra. In the thirteenth O site, O(13) is bonded in a 4-coordinate geometry to one Er(3), one Er(6), one Er(7), and one Ti(2) atom. In the fourteenth O site, O(14) is bonded to one Er(5), one Er(6), and two equivalent Ti(2) atoms to form OEr2Ti2 tetrahedra that share  a cornercorner with one O(18)Er3Ti tetrahedra, corners with two equivalent O(11)Er4 tetrahedra,  a cornercorner with one O(12)Er3Ti trigonal pyramid, and  an edgeedge with one O(16)Ti4 trigonal pyramid. In the fifteenth O site, O(15) is bonded to two equivalent Er(1), one Ti(1), and one Ti(5) atom to form OEr2Ti2 tetrahedra that share  a cornercorner with one O(2)Er2Ti2 tetrahedra,  a cornercorner with one O(8)Er3Ti tetrahedra, corners with two equivalent O(9)Er3Ti tetrahedra, corners with two equivalent O(11)Er4 tetrahedra,  a cornercorner with one O(16)Ti4 trigonal pyramid, edges with two equivalent O(17)Er2Ti2 tetrahedra, and  an edgeedge with one O(12)Er3Ti trigonal pyramid. In the sixteenth O site, O(16) is bonded to one Ti(3), one Ti(5), and two equivalent Ti(2) atoms to form OTi4 trigonal pyramids that share  a cornercorner with one O(15)Er2Ti2 tetrahedra,  a cornercorner with one O(19)Er3Ti tetrahedra,  an edgeedge with one O(14)Er2Ti2 tetrahedra, and  an edgeedge with one O(2)Er2Ti2 tetrahedra. In the seventeenth O site, O(17) is bonded to one Er(1), one Er(3), one Ti(1), and one Ti(4) atom to form distorted OEr2Ti2 tetrahedra that share  a cornercorner with one O(19)Er3Ti tetrahedra,  a cornercorner with one O(3)Er3Ti tetrahedra, corners with two equivalent O(17)Er2Ti2 tetrahedra, corners with two equivalent O(12)Er3Ti trigonal pyramids,  an edgeedge with one O(15)Er2Ti2 tetrahedra,  an edgeedge with one O(18)Er3Ti tetrahedra,  an edgeedge with one O(8)Er3Ti tetrahedra,  an edgeedge with one O(9)Er3Ti tetrahedra, and  an edgeedge with one O(11)Er4 tetrahedra. In the eighteenth O site, O(18) is bonded to one Er(6), two equivalent Er(3), and one Ti(4) atom to form OEr3Ti tetrahedra that share  a cornercorner with one O(14)Er2Ti2 tetrahedra,  a cornercorner with one O(3)Er3Ti tetrahedra,  a cornercorner with one O(9)Er3Ti tetrahedra, corners with two equivalent O(8)Er3Ti tetrahedra, corners with four equivalent O(11)Er4 tetrahedra,  an edgeedge with one O(19)Er3Ti tetrahedra, edges with two equivalent O(17)Er2Ti2 tetrahedra, and  an edgeedge with one O(12)Er3Ti trigonal pyramid. In the nineteenth O site, O(19) is bonded to one Er(7), two equivalent Er(3), and one Ti(3) atom to form distorted OEr3Ti tetrahedra that share  a cornercorner with one O(2)Er2Ti2 tetrahedra, corners with two equivalent O(17)Er2Ti2 tetrahedra, corners with three equivalent O(8)Er3Ti tetrahedra,  a cornercorner with one O(16)Ti4 trigonal pyramid,  an edgeedge with one O(18)Er3Ti tetrahedra, and edges with two equivalent O(11)Er4 tetrahedra.