Incorporation of chromium into aluminium borate 9Al2O3⋅ 2B2O3 (A9B2)
Garsche, Markus; Tillmanns, Ekkehart; Almen, Hartmut; Schneider, Hartmut; Kupčik, Vladimir
European Journal of Mineralogy Volume 3 Number 5 (1991), p. 793 - 808
published: Oct 2, 1991
manuscript accepted: Mar 8, 1991
manuscript received: Aug 30, 1990
ArtNo. ESP147050305002, Price: 29.00 €
Abstract Aluminium borate 9Al2O3-2B2O3 (A9B2) and Cr3+- rich A9B2 (≈ 10 wt % Cr2O3) were synthesized from oxide powders by solid state reactions. The fractional atomic coordinates determined from single crystal diffraction data agree comparatively well with those obtained by the Rietveld method using powder X-ray diffraction data. The crystal structure of A9B2 is similar to the structures of sillimanite, mullite and andalusite. The main structural units common to all four phases are the infinite chains of edge-sharing AlO6-octahedra running parallel to c. Chromium incorporation causes an expansion of the structure. Refinement of occupancy factors has shown the preference of Cr3+ for the octahedrally coordinated Al (1) -position.