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2005
Structure
D 2000
37- 007
Ca1-xNa2x Al2B2O7: A Structure with Tunable Density of Na+ Vacancies. —
Samples of composition Ca1-xNa2xAl 2B2O7 (0 < x ≤ 1) are prepared by solid state reaction of appropriate amounts of CaCO3, Na2CO3, Al2O3, and H3BO3 (1. 500 °C, 20 h;
2. 900 °C, 4 d). The compounds crystallize in the hexagonal space group P63/m with
Z = 2, as revealed by powder XRD and single crystal XRD for the samples with
x = 0.32 and 0.95. The structure consists of ∞2[Al2B2 O27 ] lamellae stacked along the
c axis, as in CaAl2B2O7 and Na2Al2B2O7, but with different stacking sequence. The Ca2+
and half of the Na+ cations (Na1) statistically occupy the same crystallographic site
+
between the [Al2B2 O27 ] lamellae, while the other Na cations (Na2) are located in the
planes bisecting the lamellae. Depending on the composition, the site occupation factor
of the Na2 site can vary in the same range as x, leading to a tunable density of Na+ vacancies in the structure. — (HE*, M.; OKUDERA, H.; SIMON, A.; Inorg. Chem. 44
(2005) 12, 4421-4426; MPI Festkoerperforsch., D-70569 Stuttgart, Germany; Eng.)
— Schramke
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