Al and O substitutions in Ba S-phases, Ba2AlxSi12−xN16−xO2+x: A TEM, XRD and solid-state NMR study

In a series of Ba-based oxonitrido-silicate S-phases (Ba2AlxSi12−xN16−xO2+x) spanning a compositional range up to x ≈ 3, we examine the incorporation of Al and O by 29Si and 27Al magic-angle spinning (MAS) solid state nuclear magnetic resonance (NMR) and 27Al triple-quantum MAS (3QMAS). The 3QMAS spectra reveal 27Al signals from two distinct structural environments, assigned to AlN4 or AlN3O tetrahedra, respectively, and with their relative amounts depending on the S-phase substitution parameter x. 29Si NMR show variable fractions of SiN4 and SiN3O environments. The NMR results accord overall with a structural substitution model for which O enters at one crystallographic position (occupied according to N4−xOx), in conjunction with a random Al for Si substitution at two distinct crystallographic positions. This leads to S-phase frameworks built from SiN4, SiN3O, AlN4 and AlN3O tetrahedra.

The incorporation of Al and O is studied in a series of Ba S-phases.Figure optionsDownload as PowerPoint slide