The crystal structure of highly nonstoichiometric potassium β-alumina, K1.50Al11.0O17.25

Abstract The crystal structure and cation distribution of highly nonstoichiometric potassium β-alumina K 1.50 Al 11.0 O 17.25 have been studied by single-crystal X-ray diffraction. The single crystal was obtained by ion exchange from barium β-alumina (Ba 0.75 Al 11.0 O 17.25 ) and the least-squares refinement was accomplished with a final R value of 0.029. The occupation of K ion in the mirror plane ( z = 0.25) was explained by assuming three types of cells: singlet cell (KAl 11 O 17 ), KKK triplet cell (K 3 Al 11 O 17 ), and KKOi triplet cell (K 2 O · Al 11 O 17 ) where Oi stands for interstitial oxygen. This model was shown to be applicable to the ordinary potassium β-alumina (K 1.30 Al 11.0 O 17.15 ).