Superstructure of Mullite-type KAl₉O₁₄

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) Å3, 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.

Oxo- and Oxofluoroaluminates in the RbF–Al2O3 System: Synthesis and Structural Characterization

“…This has led to the synthesis of numerous solid electrolytes with high conductivity linked to various ions, in particular to monovalent alkali-metal cations . Until now, many investigations have been focused on the structure and nonstoichiometry of oxoaluminate compounds (known as β-aluminas) containing a monovalent cation, especially Na and K. − They exhibit a “mullite” type structure, where Si 4+ cations substitute Al 3+ to induce oxygen vacancies which are required to retain the charge balance . The vacant sites in mullite type structures produce an extreme mobility of the monovalent ions, bringing high ionic conduction.…”

“…1 Until now, many investigations have been focused on the structure and nonstoichiometry of oxoaluminate compounds (known as β-aluminas) containing a monovalent cation, especially Na and K. 2−8 They exhibit a "mullite" type structure, where Si 4+ cations substitute Al 3+ to induce oxygen vacancies which are required to retain the charge balance. 9 The vacant sites in mullite type structures produce an extreme mobility of the monovalent ions, bringing high ionic conduction. Moreover, these materials demonstrate excellent stability at high temperature.…”

Breakdown mechanism of γ-Al2O3 on Ni2Al3 coatings exposed in a biomass fired power plant

“…Potassium aluminate such as KAl9O14 does not have the close packed structure of alumina [36] and presumably would allow for easier penetration of corrosive species such as Cl. In the presence of a KCl-AlCl3 molten salt, the corrosive species would be likely to be chlorine.…”

Diffuse scattering and partial disorder in complex structures

“…High-temperature ceramics such as cubic zirconias (Gallardo-Ló pez et al, 2001;Frey et al, 2005) and mullite (Lazic et al, 2013). Cubic zirconia has a simple cubic average, but the arrays of oxygen atoms contain vacancies and the metal atoms relax around these (Welberry et al, 1995).…”