Na3Ca is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to eight Na(1,1) and four equivalent Ca(1) atoms to form NaNa8Ca4 cuboctahedra that share corners with four equivalent Ca(1)Na12 cuboctahedra; corners with fourteen Na(1,1)Na8Ca4 cuboctahedra; edges with six equivalent Ca(1)Na12 cuboctahedra; edges with twelve Na(1,1)Na8Ca4 cuboctahedra; faces with four equivalent Ca(1)Na12 cuboctahedra; and faces with sixteen Na(1,1)Na8Ca4 cuboctahedra. In the second Na site, Na(1) is bonded to eight Na(1,1) and four equivalent Ca(1) atoms to form NaNa8Ca4 cuboctahedra that share corners with four equivalent Ca(1)Na12 cuboctahedra; corners with fourteen Na(1,1)Na8Ca4 cuboctahedra; edges with six equivalent Ca(1)Na12 cuboctahedra; edges with twelve Na(1,1)Na8Ca4 cuboctahedra; faces with four equivalent Ca(1)Na12 cuboctahedra; and faces with sixteen Na(1,1)Na8Ca4 cuboctahedra. Ca(1) is bonded to twelve Na(1,1) atoms to form CaNa12 cuboctahedra that share corners with six equivalent Ca(1)Na12 cuboctahedra; corners with twelve equivalent Na(1)Na8Ca4 cuboctahedra; edges with eighteen Na(1,1)Na8Ca4 cuboctahedra; faces with eight equivalent Ca(1)Na12 cuboctahedra; and faces with twelve Na(1,1)Na8Ca4 cuboctahedra.
Na3Ca is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to eight Na(1,1) and four equivalent Ca(1) atoms to form NaNa8Ca4 cuboctahedra that share corners with four equivalent Ca(1)Na12 cuboctahedra; corners with fourteen Na(1,1)Na8Ca4 cuboctahedra; edges with six equivalent Ca(1)Na12 cuboctahedra; edges with twelve Na(1,1)Na8Ca4 cuboctahedra; faces with four equivalent Ca(1)Na12 cuboctahedra; and faces with sixteen Na(1,1)Na8Ca4 cuboctahedra. There are a spread of Na(1)-Na(1,1) bond distances ranging from 3.72-3.90 Å. There are two shorter (3.81 Å) and two longer (3.82 Å) Na(1)-Ca(1) bond lengths. In the second Na site, Na(1) is bonded to eight Na(1,1) and four equivalent Ca(1) atoms to form NaNa8Ca4 cuboctahedra that share corners with four equivalent Ca(1)Na12 cuboctahedra; corners with fourteen Na(1,1)Na8Ca4 cuboctahedra; edges with six equivalent Ca(1)Na12 cuboctahedra; edges with twelve Na(1,1)Na8Ca4 cuboctahedra; faces with four equivalent Ca(1)Na12 cuboctahedra; and faces with sixteen Na(1,1)Na8Ca4 cuboctahedra. All Na(1)-Na(1) bond lengths are 3.76 Å. There are two shorter (3.81 Å) and two longer (3.82 Å) Na(1)-Ca(1) bond lengths. Ca(1) is bonded to twelve Na(1,1) atoms to form CaNa12 cuboctahedra that share corners with six equivalent Ca(1)Na12 cuboctahedra; corners with twelve equivalent Na(1)Na8Ca4 cuboctahedra; edges with eighteen Na(1,1)Na8Ca4 cuboctahedra; faces with eight equivalent Ca(1)Na12 cuboctahedra; and faces with twelve Na(1,1)Na8Ca4 cuboctahedra.