THE STRUCTURE OF La₂₆(BO₃)₈O_27. E. Schweda,^a K. Wurst, ^b J.H. Lin, ^c M.Z. Su ^aInstitut fur Anorganische Chemie, Universität Tübingen, Germany ^bInst. für Allg. und Anorg. Chemie, Universität Innsbruck, Austria ^cDept. of Materials Chemistry, Peking University, Beijing 100871, China

Previously La₂₆(BO₃)₈O₂₇ was described as La₃BO₆ with the remark that the samples contain a small amount of unreacted oxide [1]. Very small colourless crystals of La₂₆(BO₃)₈O₂₇ were grown from La₂O₃ and H₃BO₃. La₂₆(BO₃)₈O₂₇ crystallizes in the monoclinic space group P2₁/c with the lattice constants a = 692.0(1) pm, b = 1292.3(1) pm, c = 1457.1(1) pm and [[beta]] = 99.41(1)deg..

A close inspection of this structure reveals a certain relationship to the (CaF₂) fluorite structure, both from the structure and the composition point of view. At a first sight, neglecting the boron atoms in the structure, the composition will be close to "LaO₂" (La₂₆O_52-xB₈). Furthermore the structure of La₂₆(BO₃)₈O₂₇ can be considered as a distorted version of the fluorite structure. To emphasize this feature one of the "fluorite" layers with a stacking sequence O-La-O is presented in fig. 1. The sheets are oriented perpendicular to the [101] lattice direction.

Acknowledgments

Financial support for this work was received from Fonds der Chemischen Industrie.

References

1. Gmelin Handbook RE Main Vol.C 11b, p.390