title: Superstructure of Mullite-type KAl9O14.
abstract: Large whiskers of a new KAl9O14polymorph 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 groupP21/n(a= 8.1880(8),b= 7.6760(7),c= 8.7944(9) Å, β = 110.570(8)°,V= 517.50(9) Å3,Z= 2). Crystals of KAl9O14exhibit a mullite-type structure with linear edge-sharing AlO6octahedral chains connected with groups of two AlO4tetrahedra and one AlO5trigonal bipyramid. Additionally, disproportionation of KAl9O14into K β-alumina and corundum was observed using in situ high-temperature optical microscopy and Raman spectroscopy.
authors.affiliation: Mineralogical Crystallography, Institute of Geological Sciences, University of Bern , Freiestrasse 3, 3012 Bern, Switzerland.
authors.forename: Biljana
authors.initials: B
authors.lastname: Lazic
authors.forename: Hannes
authors.initials: H
authors.lastname: Krüger
authors.forename: Reinhard
authors.initials: R
authors.lastname: Kaindl
authors.forename: Lukas
authors.initials: L
authors.lastname: Perfler
authors.forename: Aleksandar
authors.initials: A
authors.lastname: Kremenović
authors.forename: Vladica
authors.initials: V
authors.lastname: Cvetković
authors.forename: Ray L
authors.initials: RL
authors.lastname: Withers
keywords: diffuse scattering; mullite-type; stacking faults; superstructure; whiskers