Superstructure of Mullite-type KAl(9)O(14)

[Image: see text] Large whiskers of a new KAl(9)O(14) 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 P2(1)/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 KAl(9)O(14) exhibit a mullite-type structure with linear edge-sharing AlO(6) octahedral chains connected with groups of two AlO(4) tetrahedra and one AlO(5) trigonal bipyramid. Additionally, disproportionation of KAl(9)O(14) into K β-alumina and corundum was observed using in situ high-temperature optical microscopy and Raman spectroscopy.