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Title: Crystal-chemistry of mullite-type aluminoborates Al{sub 18}B{sub 4}O{sub 33} and Al{sub 5}BO{sub 9}: A stoichiometry puzzle

Orthorhombic Al{sub 2}O{sub 3}-rich aluminoborate is an important ceramic material for which two slightly different compositions have been assumed: Al{sub 5}BO{sub 9} (5Al{sub 2}O{sub 3}:B{sub 2}O{sub 3}) and Al{sub 18}B{sub 4}O{sub 33} (9Al{sub 2}O{sub 3}:2B{sub 2}O{sub 3}). The formula Al{sub 18}B{sub 4}O{sub 33} (=Al{sub 4.91}B{sub 1.09}O{sub 9}) was derived from results of chemical analyses when crystal structure data were not yet available. Subsequent structural investigations indicated Al{sub 5}BO{sub 9} composition. Nevertheless, Al{sub 18}B{sub 4}O{sub 33} was still accepted as the correct stoichiometry assuming that additional B replaces 9% Al. Powder samples of both compositions and ones with excess boron were prepared by solid state reactions between {alpha}-Al{sub 2}O{sub 3} and B{sub 2}O{sub 3}/H{sub 3}BO{sub 3} at temperatures above 1100 {sup o}C and single-crystals were grown from flux at 1100 and 1550 {sup o}C. Products were investigated by single-crystal and powder XRD, {sup 11}B and {sup 27}Al solid-state MAS-NMR, Raman and FTIR spectroscopy as well as Laser-ablation ICP-MS. No indication of the predicted 9% B{yields}Al substitution was found. LA ICP-MS indicated 12.36(27) wt% B{sub 2}O{sub 3} corresponding to Al{sub 4.97}B{sub 1.03}O{sub 9}. Hence, the suggested Al{sub 18}B{sub 4}O{sub 33} stoichiometry can be excluded for all synthesized samples. A very low amountmore » of Al vacancies at a five-fold coordinated site are likely, charge balanced by an additional nearby three-fold coordinated B site. All evidences indicate that the title compound should be reported as Al{sub 5-x}B{sub 1+x}O{sub 9} with x<0.038(6), which is close to Al{sub 5}BO{sub 9}. -- Graphical abstract: A chemical composition of Al{sub 18}B{sub 4}O{sub 33}=Al{sub 4.91}B{sub 1.09}O{sub 9}=9Al{sub 2}O{sub 3}:2B{sub 2}O{sub 3} has been assumed for mullite-type aluminoborate with Al{sub 5}BO{sub 9} structure. However, samples prepared by different routes showed compositions close to 5Al{sub 2}O{sub 3}:B{sub 2}O{sub 3}. Display Omitted« less
Authors:
 [1] ;  [1] ;  [2] ;  [3] ;  [4]
  1. Mineralogical Crystallography, Institute of Geological Sciences, University of Bern, Freiestrasse 3, CH-3012 Bern (Switzerland)
  2. EMPA, Swiss Federal Laboratories for Materials Science and Research, Laboratory for Functional Polymers, Uberlandstrasse 129, CH-8600 Duebendorf (Switzerland)
  3. Institut fuer Mineralogie und Kristallographie, Universitaet Wien - Geozentrum, Althanstrasse 14, A-1090 Wien (Austria)
  4. Rock-Water Interaction Group, Institute of Geological Sciences, University of Bern, Baltzerstrasse 1-3, CH-3012 Bern (Switzerland)
Publication Date:
OSTI Identifier:
21494176
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 184; Journal Issue: 1; Other Information: DOI: 10.1016/j.jssc.2010.10.032; PII: S0022-4596(10)00489-5; Copyright (c) 2010 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABLATION; ALUMINIUM OXIDES; BORATES; BORIC ACID; BORON OXIDES; CERAMICS; CHEMICAL ANALYSIS; CHEMICAL COMPOSITION; ICP MASS SPECTROSCOPY; INFRARED SPECTRA; MONOCRYSTALS; MULLITE; NMR SPECTRA; NUCLEAR MAGNETIC RESONANCE; ORTHORHOMBIC LATTICES; STOICHIOMETRY; TEMPERATURE RANGE 1000-4000 K; VACANCIES; X-RAY DIFFRACTION ALUMINIUM COMPOUNDS; BORON COMPOUNDS; CHALCOGENIDES; COHERENT SCATTERING; CRYSTAL DEFECTS; CRYSTAL LATTICES; CRYSTAL STRUCTURE; CRYSTALS; DIFFRACTION; HYDROGEN COMPOUNDS; INORGANIC ACIDS; INORGANIC COMPOUNDS; INORGANIC ION EXCHANGERS; ION EXCHANGE MATERIALS; MAGNETIC RESONANCE; MASS SPECTROSCOPY; MATERIALS; MINERALS; OXIDE MINERALS; OXIDES; OXYGEN COMPOUNDS; POINT DEFECTS; RESONANCE; SCATTERING; SPECTRA; SPECTROSCOPY; TEMPERATURE RANGE