Na3Ca2TaO6 is Caswellsilverite-derived structured and crystallizes in the orthorhombic Fddd space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form NaO6 octahedra that share corners with two equivalent Ta(1)O6 octahedra, corners with four equivalent Ca(1)O6 octahedra, edges with two equivalent Ta(1)O6 octahedra, edges with four equivalent Ca(1)O6 octahedra, and edges with six equivalent Na(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-16°. In the second Na site, Na(2) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form NaO6 octahedra that share corners with two equivalent Na(2)O6 octahedra, corners with two equivalent Ca(1)O6 octahedra, corners with two equivalent Ta(1)O6 octahedra, edges with two equivalent Na(2)O6 octahedra, edges with two equivalent Ta(1)O6 octahedra, edges with three equivalent Na(1)O6 octahedra, and edges with five equivalent Ca(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 3-17°. Ca(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form CaO6 octahedra that share corners with two equivalent Na(1)O6 octahedra, corners with two equivalent Na(2)O6 octahedra, corners with two equivalent Ca(1)O6 octahedra, edges with two equivalent Na(1)O6 octahedra, edges with two equivalent Ca(1)O6 octahedra, edges with three equivalent Ta(1)O6 octahedra, and edges with five equivalent Na(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 14-18°. Ta(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form TaO6 octahedra that share corners with two equivalent Na(1)O6 octahedra, corners with four equivalent Na(2)O6 octahedra, edges with two equivalent Na(1)O6 octahedra, edges with four equivalent Na(2)O6 octahedra, and edges with six equivalent Ca(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-3°. There are two inequivalent O sites. In the first O site, O(1) is bonded to one Na(1), two equivalent Na(2), two equivalent Ca(1), and one Ta(1) atom to form a mixture of distorted corner and edge-sharing ONa3Ca2Ta octahedra. The corner-sharing octahedral tilt angles range from 0-12°. In the second O site, O(2) is bonded to one Na(1), two equivalent Na(2), two equivalent Ca(1), and one Ta(1) atom to form a mixture of distorted corner and edge-sharing ONa3Ca2Ta octahedra. The corner-sharing octahedral tilt angles range from 2-12°.
Na3Ca2TaO6 is Caswellsilverite-derived structured and crystallizes in the orthorhombic Fddd space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form NaO6 octahedra that share corners with two equivalent Ta(1)O6 octahedra, corners with four equivalent Ca(1)O6 octahedra, edges with two equivalent Ta(1)O6 octahedra, edges with four equivalent Ca(1)O6 octahedra, and edges with six equivalent Na(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-16°. Both Na(1)-O(1) bond lengths are 2.76 Å. All Na(1)-O(2) bond lengths are 2.39 Å. In the second Na site, Na(2) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form NaO6 octahedra that share corners with two equivalent Na(2)O6 octahedra, corners with two equivalent Ca(1)O6 octahedra, corners with two equivalent Ta(1)O6 octahedra, edges with two equivalent Na(2)O6 octahedra, edges with two equivalent Ta(1)O6 octahedra, edges with three equivalent Na(1)O6 octahedra, and edges with five equivalent Ca(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 3-17°. Both Na(2)-O(1) bond lengths are 2.41 Å. There are two shorter (2.46 Å) and two longer (2.60 Å) Na(2)-O(2) bond lengths. Ca(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form CaO6 octahedra that share corners with two equivalent Na(1)O6 octahedra, corners with two equivalent Na(2)O6 octahedra, corners with two equivalent Ca(1)O6 octahedra, edges with two equivalent Na(1)O6 octahedra, edges with two equivalent Ca(1)O6 octahedra, edges with three equivalent Ta(1)O6 octahedra, and edges with five equivalent Na(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 14-18°. Both Ca(1)-O(1) bond lengths are 2.33 Å. There are two shorter (2.37 Å) and two longer (2.38 Å) Ca(1)-O(2) bond lengths. Ta(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form TaO6 octahedra that share corners with two equivalent Na(1)O6 octahedra, corners with four equivalent Na(2)O6 octahedra, edges with two equivalent Na(1)O6 octahedra, edges with four equivalent Na(2)O6 octahedra, and edges with six equivalent Ca(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-3°. Both Ta(1)-O(1) bond lengths are 2.03 Å. All Ta(1)-O(2) bond lengths are 2.04 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded to one Na(1), two equivalent Na(2), two equivalent Ca(1), and one Ta(1) atom to form a mixture of distorted corner and edge-sharing ONa3Ca2Ta octahedra. The corner-sharing octahedral tilt angles range from 0-12°. In the second O site, O(2) is bonded to one Na(1), two equivalent Na(2), two equivalent Ca(1), and one Ta(1) atom to form a mixture of distorted corner and edge-sharing ONa3Ca2Ta octahedra. The corner-sharing octahedral tilt angles range from 2-12°.