Mixed valent niobium nitrides and oxynitrides resulting from ammonolysis of alkaline niobates

Nitridation of alkaline niobates MNbO3 and MNb3O8 (M = Li, Na, K) in flowing ammonia leads to different reaction products depending on the temperature and the considered niobate. Two series of mixed valent NaCl-type oxynitrides are formed in the Li-Nb-O-N system. A complete nitrogen/oxygen substitution can be obtained since the ternary oxide LiNb3O8 is transformed, without lithium evaporation, into a ternary nitride LiNb3N4 which has a filled up MoS2-type structure. Reaction of sodium or potassium niobates with NH3 results in a total evaporation of sodium or potassium and formation of the binary nitride Nb4N5 closely related to the NaCl structure. (C) 1997 Elsevier Science S.A.