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. δ₁-MoN is best described by the WC-type structure with stacking faults due to nitrogen atom disorder. Ordering of nitrogen atoms results in δ₂-MoN with the NiAs-type structure. Formation of trigonal molybdenum clusters in δ₃-MoN is responsible for the doubling of the unit cell in a and b directions compared to δ₂-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.