A crystal-chemical analysis was made of the possible positions of interstitial Fe3+ cations. It was shown that the geometrically preferred position had the coordinates: (0.25, 0.35, 0.125). This was close to a position that had been predicted on the basis of EXAFS data. The incorporation of the impurity cation was expected to be accompanied by the formation of one H atom and two K vacancies.

T.A.Eremina, V.A.Kuznetsov, T.M.Okhrimenko, N.G.Furmanova: Kristallografiya, 1996, 41[4], 717-21 (Crystallography Reports, 1996, 41[4], 680-4)