Abstract
The crystal structure of calzirtite, Ca2Zr5 (Ti1.5Nbo.29Fe0.18)O16, a = 15.094(2), c = 10.043(2) Å, space group I41/acd, Z = 8 has been refined by the method of least-squares using 1327 reflections to an R index of 0.040 (Rw = 0.047). The data were collected on a four-circle diffractometer using graphite-monochromated MoKα radiation. The cations occupy fluorite-type positions in the tetragonal cell. They are ordered into planes parallel to (010) and form two layers containing Ti, Ca, and Zr sandwiched between layers of 7- and 8-coordinated Zr. At the 8-coordinate site, Zr shows a statistical displacement off special position 8(b). Corner-linked TiO6 octahedra form chains that zig-zag parallel to c. The results are in agreement with those obtained from a powder refinement of synthetic calzirtite by Rossell (1982, Acta Crystallographica, B38, 593-595).