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Superstructure of Mullite-type KAl9O14.

Research paper by Biljana B Lazic, Hannes H Krüger, Reinhard R Kaindl, Lukas L Perfler, Aleksandar A Kremenović, Vladica V Cvetković, Ray L RL Withers

Indexed on: 19 Mar '13Published on: 19 Mar '13Published in: Chemistry of Materials



Abstract

Large whiskers of a new KAl9O14 polymorph with mullite-type structure were synthesized. The chemical composition of the crystals was confirmed by energy-dispersive X-ray spectroscopy, and the structure was determined using single-crystal X-ray diffraction. Nanosized twin domains and one-dimensional diffuse scattering were observed utilizing transmission electron microscopy. The compound crystallizes in space group P21/n (a = 8.1880(8), b = 7.6760(7), c = 8.7944(9) Å, β = 110.570(8)°, V = 517.50(9) Å(3), Z = 2). Crystals of KAl9O14 exhibit a mullite-type structure with linear edge-sharing AlO6 octahedral chains connected with groups of two AlO4 tetrahedra and one AlO5 trigonal bipyramid. Additionally, disproportionation of KAl9O14 into K β-alumina and corundum was observed using in situ high-temperature optical microscopy and Raman spectroscopy.