Electronic Structure of Substoichiometric Tantalum Nitrides Studied by the XES Method

The X-ray emission spectroscopy (XES) method has been used to study the electronic structure of substoichiometric tantalum mononitrides. Both the Ta Lβ 5 and N Kα X-ray emission spectra of cubic nitrides TaN x (Nacl structure, 0.81 ≤ x ≤ 1.172), hexagonal nitrides TaN 0.99 (CoSn structure) and TaN 0.90 (WC structure) have been derived and compared on a common energy scale. In the sequence TaN (CoSn structure) → TaN (WC structure) → TaN (NaCl structure) a decrease of the N Kα band halfwidth was observed. In most substoichiometric cubic tantalum mononitrides with vacancies on the metal sublattice (1.134 ≤ x ≤ 1.172) a subband of non-bonding N 2p-like states appeared in the energy region between the Ta 5d-N 2p- and Ta Sd-like bands. In all tantalum nitrides studied the Ta 5d-like and N 2p-like states are strongly hybridized, and a charge transfer occurs from Ta to N atoms.