Acta Crystallographica Section B

Structural Science

Volume 55, Part 3 (June 1999)

research papers

Acta Cryst. (1999). B55, 313-320 [ doi:10.1107/S0108768198014268 ]

The crystal structure of Ca₇Zr₇Ta₆O₃₆ refined using synchrotron-radiation data

S. Schmid, J. G. Thompson, R. L. Withers, C. D. Ling, N. Ishizawa and S. Kishimoto

Abstract: Single-crystal X-ray diffraction data [synchrotron radiation; [lambda] = 1.2682 (4) Å] are used to solve and refine the crystal structure of heptacalcium hexatantalum heptazirconium hexatriacontaoxide, Ca₇Zr₇Ta₆O₃₆. The structure adopts space group Fddd with cell dimensions a = 36.394 (1), b = 7.3674 (5), c = 31.006 (2) Å. The structure was solved by direct methods. Refinement using 1299 unique reflections leads to final values of R = 0.031 and wR = 0.034. The refined metal-atom ordering scheme is far from fully ordered and reminiscent of the A/B metal-atom ordering characteristic of the pyrochlore structure type. Bond-valence sums are calculated to confirm the plausibility of the crystal chemistry of Ca₇Zr₇Ta₆O₃₆.