Structure of Tantalum Nitrides

The crystal structure of tantalum nitrides is examined by X-ray and electron diffraction techniques and the following seven phases are identified: TaN ∼0.05 (cubic, β-phase), Ta 2 N (hexagonal, γ-phase), δ-TaN (hexagonal), ε -TaN (hexagonal), Ta 5 N 6 (hexagonal), Ta 4 N 5 (tetragonal) and Ta 3 N 5 (tetragonal or monoclinic). Thin films of Ta nitrides for electron diffraction study were prepared by nitriding thin evaporated films of tantalum in ammonia and nitrogen. By heating thin films of Ta 3 N 5 in vacuum, the phase transformations occur successively as follows: Ta 3 N 5 →Ta 4 N 5 →Ta 5 N 6 → ε -TaN→Ta 2 N. The stucture of each nitride form is discussed.