The crystal structure of α-K3AIF6: Elpasolites and double perovskites with broken corner-sharing connectivity of the octahedral framework

Artem M. Abakumov, Graham King, Veronika K. Laurinavichute, Marina G. Rozova, Patrick M. Woodward, Evgeny V. Antipov

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26 Citations (Scopus)

Abstract

The crystal structure of α-K3AIF6 was solved and refined from a combination of powder X-ray and neutron diffraction data (a = 18.8385(3)Å, c = 33.9644(6)Å, S.G. /41 Z= 80, R P(X-ray) = 0.037, Rp(neutron) = 0.053). The crystal structure is of the A2BB′X6 elpasolite type with the a = b ≈ ae√5, c = 4ae superstructure (a e, parameter of the elpasolite subcell) and rock-salt-type ordering of the K and Al cations over the B and B′ positions, respectively. The remarkable feature of α-K3AIF6 Is a rotation of 2/5 of the AIF6 octahedra by ∼π/4 around one of the crystal axes of the elpasollte subcell, coinciding with the 4-fold symmetry axes of the AIF6 octahedra. The rotation of the AIF6 octahedra replaces the corner-sharing between the K and AI polyhedra by edge-sharing, resulting In an increase of coordination numbers of the K cations at the B positions up to 7 and 8. Due to significant deformations of the K polyhedra, the corner-sharing connectivity of the octahedral elpasolite framework Is broken and the rotations of the AIF6 octahedra do not have a cooperative character. Elpasolites and double perovskites with similar structural organization are discussed. The difference in ionic radii of the B and B′ cations as well as the tolerance factor are proposed to be the parameters governing the formation of elpasolites and double perovskites with broken corner-sharing connectivity of the octahedral framework.

Original languageEnglish
Pages (from-to)9336-9344
Number of pages9
JournalInorganic Chemistry
Volume48
Issue number19
DOIs
Publication statusPublished - 2009
Externally publishedYes

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