The crystal structure of mayenite (ideal composition: Ca12Al14O33) consists of a (disordered) calcium-aluminate framework comprising 32 of the 33 oxygen anions. It contains large open cages, 1/6 of them being filled randomly by the remaining “free” O which was available for diffusion and very high ionic conductivities. This extra-framework O could be replaced by N; opening up possibilities for a pure N ionic conductor. From high-temperature neutron powder diffraction experiments, data analysis employing difference Fourier methods and anharmonic Debye-Waller factors and comparing pure O-mayenite with partly exchanged N/O-mayenite it was concluded that O diffusion proceeded via jump-like processes, intimately coupled to

relaxations of Ca and involving exchange of the so-called free O with framework O, while N diffusion appeared to proceed via an interstitial process.

Anion Diffusion Processes in O- and N-Mayenite Investigated by Neutron Powder Diffraction. H.Boysen, I.Kaiser-Bischoff, M.Lerch: Diffusion Fundamentals, 2008, 8, 8.1