Oxygen–nitrogen ordering in yttrium nitrogen melilite

Abstract

Nitrogen-15 NMR studies of yttrium nitrogen melilite (Y₂Si₃O₃N₄) show that, contrary to previous work based only on ²⁹Si 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 Si₂(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.