Crystal-chemistry of mullite-type aluminoborates Al18B4O33 and Al5BO9: A stoichiometry puzzle
- Author(s)
- Martin Fisch, Thomas Armbruster, Daniel Rentsch, Eugen Libowitzky, Thomas Pettke
- Abstract
Orthorhombic Al2O3-rich aluminoborate is an important ceramic material for which two slightly different compns. have been assumed: Al5BO9 (5Al2O3:B2O3) and Al18B4O33 (9Al2O3:2B2O3). The formula Al18B4O33 (=Al4.91B1.09O9) was derived from results of chem. analyses when crystal structure data were not yet available. Subsequent structural investigations indicated Al5BO9 compn. Nevertheless, Al18B4O33 was still accepted as the correct stoichiometry assuming that addnl. B replaces 9% Al. Powder samples of both compns. and ones with excess boron were prepd. by solid state reactions between .alpha.-Al2O3 and B2O3/H3BO3 at temps. above 1100 C and single-crystals were grown from flux at 1100 and 1550 C. Products were investigated by single-crystal and powder XRD, 11B and 27Al solid-state MAS-NMR, Raman and FTIR spectroscopy as well as Laser-ablation ICP-MS. No indication of the predicted 9% BAl substitution was found. LA ICP-MS indicated 12.36(27) wt% B2O3 corresponding to Al4.97B1.03O9. Hence, the suggested Al18B4O33 stoichiometry can be excluded for all synthesized samples. A very low amt. of Al vacancies at a five-fold coordinated site are likely, charge balanced by an addnl. nearby three-fold coordinated B site. All evidences indicate that the title compd. should be reported as Al5-xB1+xO9 with x
- Organisation(s)
- Department of Mineralogy and Crystallography
- External organisation(s)
- Universität Bern, Eidgenössische Materialprüfungs- und Forschungsanstalt
- Journal
- Journal of Solid State Chemistry
- Volume
- 184
- Pages
- 70-80
- No. of pages
- 11
- ISSN
- 0022-4596
- Publication date
- 2011
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 105113 Crystallography
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/33132d0c-bbee-4663-83cc-2d93b1cb9734