Ba2EuTi2Ta3O15 crystallizes in the orthorhombic Pbam space group. Ba(1) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(2), and two equivalent O(7) atoms. Eu(1) is bonded to two equivalent O(5), two equivalent O(6), four equivalent O(3), and four equivalent O(4) atoms to form EuO12 cuboctahedra that share faces with two equivalent Eu(1)O12 cuboctahedra, faces with four equivalent Ti(1)O6 octahedra, and faces with four equivalent Ta(1)O6 octahedra. Ti(1) is bonded to one O(2), one O(3), one O(4), one O(7), and two equivalent O(5) atoms to form TiO6 octahedra that share  a cornercorner with one Ta(2)O6 octahedra, corners with two equivalent Ti(1)O6 octahedra, corners with three equivalent Ta(1)O6 octahedra, and faces with two equivalent Eu(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 6-36°. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(1), one O(3), one O(4), one O(7), and two equivalent O(6) atoms to form TaO6 octahedra that share  a cornercorner with one Ta(2)O6 octahedra, corners with two equivalent Ta(1)O6 octahedra, corners with three equivalent Ti(1)O6 octahedra, and faces with two equivalent Eu(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 6-36°. In the second Ta site, Ta(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(8) atoms to form TaO6 octahedra that share corners with two equivalent Ti(1)O6 octahedra, corners with two equivalent Ta(1)O6 octahedra, and corners with two equivalent Ta(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-35°. There are eight inequivalent O sites. In the first O site, O(5) is bonded in a 2-coordinate geometry to one Eu(1) and two equivalent Ti(1) atoms. In the second O site, O(6) is bonded in a 2-coordinate geometry to one Eu(1) and two equivalent Ta(1) atoms. In the third O site, O(7) is bonded in a 4-coordinate geometry to two equivalent Ba(1), one Ti(1), and one Ta(1) atom. In the fourth O site, O(8) is bonded in a linear geometry to two equivalent Ta(2) atoms. In the fifth O site, O(1) is bonded in a distorted bent 150 degrees geometry to two equivalent Ba(1), one Ta(1), and one Ta(2) atom. In the sixth O site, O(2) is bonded in a distorted bent 150 degrees geometry to two equivalent Ba(1), one Ti(1), and one Ta(2) atom. In the seventh O site, O(3) is bonded in a distorted linear geometry to two equivalent Eu(1), one Ti(1), and one Ta(1) atom. In the eighth O site, O(4) is bonded in a distorted linear geometry to two equivalent Eu(1), one Ti(1), and one Ta(1) atom.
Ba2EuTi2Ta3O15 crystallizes in the orthorhombic Pbam space group. Ba(1) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(2), and two equivalent O(7) atoms. Both Ba(1)-O(1) bond lengths are 2.85 Å. Both Ba(1)-O(2) bond lengths are 2.90 Å. Both Ba(1)-O(7) bond lengths are 2.80 Å. Eu(1) is bonded to two equivalent O(5), two equivalent O(6), four equivalent O(3), and four equivalent O(4) atoms to form EuO12 cuboctahedra that share faces with two equivalent Eu(1)O12 cuboctahedra, faces with four equivalent Ti(1)O6 octahedra, and faces with four equivalent Ta(1)O6 octahedra. Both Eu(1)-O(5) bond lengths are 2.60 Å. Both Eu(1)-O(6) bond lengths are 2.65 Å. All Eu(1)-O(3) bond lengths are 2.73 Å. All Eu(1)-O(4) bond lengths are 2.74 Å. Ti(1) is bonded to one O(2), one O(3), one O(4), one O(7), and two equivalent O(5) atoms to form TiO6 octahedra that share  a cornercorner with one Ta(2)O6 octahedra, corners with two equivalent Ti(1)O6 octahedra, corners with three equivalent Ta(1)O6 octahedra, and faces with two equivalent Eu(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 6-36°. The Ti(1)-O(2) bond length is 1.90 Å. The Ti(1)-O(3) bond length is 1.99 Å. The Ti(1)-O(4) bond length is 2.01 Å. The Ti(1)-O(7) bond length is 1.99 Å. Both Ti(1)-O(5) bond lengths are 1.99 Å. There are two inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(1), one O(3), one O(4), one O(7), and two equivalent O(6) atoms to form TaO6 octahedra that share  a cornercorner with one Ta(2)O6 octahedra, corners with two equivalent Ta(1)O6 octahedra, corners with three equivalent Ti(1)O6 octahedra, and faces with two equivalent Eu(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 6-36°. The Ta(1)-O(1) bond length is 1.97 Å. The Ta(1)-O(3) bond length is 2.00 Å. The Ta(1)-O(4) bond length is 1.97 Å. The Ta(1)-O(7) bond length is 1.98 Å. Both Ta(1)-O(6) bond lengths are 1.99 Å. In the second Ta site, Ta(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(8) atoms to form TaO6 octahedra that share corners with two equivalent Ti(1)O6 octahedra, corners with two equivalent Ta(1)O6 octahedra, and corners with two equivalent Ta(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-35°. Both Ta(2)-O(1) bond lengths are 1.99 Å. Both Ta(2)-O(2) bond lengths are 1.98 Å. Both Ta(2)-O(8) bond lengths are 1.98 Å. There are eight inequivalent O sites. In the first O site, O(5) is bonded in a 2-coordinate geometry to one Eu(1) and two equivalent Ti(1) atoms. In the second O site, O(6) is bonded in a 2-coordinate geometry to one Eu(1) and two equivalent Ta(1) atoms. In the third O site, O(7) is bonded in a 4-coordinate geometry to two equivalent Ba(1), one Ti(1), and one Ta(1) atom. In the fourth O site, O(8) is bonded in a linear geometry to two equivalent Ta(2) atoms. In the fifth O site, O(1) is bonded in a distorted bent 150 degrees geometry to two equivalent Ba(1), one Ta(1), and one Ta(2) atom. In the sixth O site, O(2) is bonded in a distorted bent 150 degrees geometry to two equivalent Ba(1), one Ti(1), and one Ta(2) atom. In the seventh O site, O(3) is bonded in a distorted linear geometry to two equivalent Eu(1), one Ti(1), and one Ta(1) atom. In the eighth O site, O(4) is bonded in a distorted linear geometry to two equivalent Eu(1), one Ti(1), and one Ta(1) atom.