David S. Bem

Synthesis of New Nitrides Using Solid State Oxide Precursors

Several novel transition metal nitrides were synthesized via ammonolysis of solid state oxide precursors at temperatures ranging from 700°C-900°C and reaction times ranging from 12 hours to 4 days. Both intermetallic nitrides, Fe 3 Mo 3 N and Co 3 Mo 3 N, and ionic/covalent nitrides, FeWN 2 , MnWN 2 , Ta 5 N 6 and Nb 5 N 6 , were prepared by this method. The products were characterized by powder X-ray diffraction and their structures were determined by powder X-ray Rietveld refinement. The intermetallic nitrides were found to be isostructural with the eta-carbide structure, Fe 3 W 3 C, while the ionic/covalent nitrides have layered structures, with metals in octahedral and trigonal prismatic coordination environments. Two polymorphs of the MnWN 2 composition, α-MnWN 2 and β-MnWN 2 , were isolated after ammonolysis at 700°C and 800°C, respectively. While the alpha phase can be converted into the beta phase by heating to 800°C under ammonia, annealing the beta phase at 700°C did not result in a structural transformation. Magnetic measurements show that FeWN 2 orders antiferromagnetically at 45K. The magnetic ordering temperature was confirmed by M6ssbauer spectroscopy. All the other nitrides were paramagnetic down to 5K. Conductivity measurements show that FeWN 2 and MnWN 2 are metallic.

Recent developments in ternary nitride chemistry

Recent developments in the synthesis, structures, and properties of ionic/covalent ternary nitrides are reviewed. A description, including synthetic conditions, is given of preparative methods reported in the literature. Solid state synthetic reactions from binary nitrides as well as novel synthetic approaches such as amide synthesis and ammonolysis of ternary oxides are described. Examples of common structure types as well as electronic and magnetic properties are discussed.

Structures of new nitrides prepared using solid oxide precursors

Several novel transition metal nitrides and oxynitrides were synthesized via ammonolysis of solid state oxide precursors at temperatures ranging from 700 C--900 C and reaction times ranging from 12 hours to 4 days. The products were characterized by powder X-ray diffraction and their structures were determined by powder X-ray Rietveld refinement. The relationships between the structures of these nitrides and oxynitrides, and their similarity to the structures of the transition metal dichalcogenides, is discussed.

Synthesis and Characterization of a New Ternary Transition Metal Nitride, FeWN 2 , from the Transition Metal Oxide Precursor, FeWO 4

The ternary nitride, FeWN2, has been synthesized via ammonolysis of the transition metal tungstate, FeWO4. FeWN2 is hexagonal with a unit cell of a = 2.8724(1) A and c =10.973(4) A. Rietveld refinements were performed in the space group P3–1C with Rwp=9.91%, and Rp=7.23%. The structure consist of alternating octahedrally coordinated iron-nitrogen layers and trigonal prismatically coordinated tungsten-nitrogen layers. Mossbauer data at 250K indicates an isomer shift δ=0.85 and shows no quadrupole splitting, which is consistent with the octahedral iron coordination in the proposed structure.