Synthesis and characterisation of hexagonal molybdenum nitrides

Four hexagonal molybdenum nitrides-three modifications of δ-MoN and Mo5N6-were prepared by the plasma-enhanced chemical vapour deposition (PECVD) method and ammonolysis of MoCl5 and MoS2. The nitrides were structurally characterised by X-ray diffraction, high-resolution transmission electron microscopy, and selected area electron diffraction. δ 1-MoN is best described by the WC-type structure with stacking faults due to nitrogen atom disorder. Ordering of nitrogen atoms results in δ 2-MoN with the NiAs-type structure. Formation of trigonal molybdenum clusters in δ 3-MoN is responsible for the doubling of the unit cell in a and b directions compared to δ 2-MoN. Mo5N6 can be viewed as an intergrowth structure of the WC- and NiAs-type building blocks, accompanied by vacancies on Mo sites. Influence of reaction conditions on the formation of the four nitrides is discussed; their magnetic properties are presented. - Graphical abstract: Hexagonal δ 2-MoN with the NiAs-type crystal structure