Oxygen-nitrogen ordering in yttrium nitrogen melilite

Nitrogen-15 NMR studies of yttrium nitrogen melilite (Y2Si3O3N4) show that, contrary to previous work based only on Si-29 NMR results, the oxygen and nitrogen atoms are ordered in a way that is entirely consistent with Pauling's rules. Nitrogen atoms occupy bridging sites and oxygen atoms occupy terminal sites in the Si-2(O,N)(7) units, while for the remaining two tetrahedra in the unit cell, oxygen and nitrogen atoms are disordered but with an overall composition of three nitrogens and one oxygen in each tetrahedron. This type of ordering behaviour is consistent with O/N ordering observed in other crystalline Y-Si-O-N ceramics.