ELECTRONIC-STRUCTURE OF SUBSTOICHIOMETRIC TANTALUM NITRIDES STUDIED BY THE XES METHOD

The X-ray emission spectroscopy (XES) method has been used to study th e electronic structure of substoichiometric tantalum mononitrides. Bot h the Ta L beta(5) and N K alpha X-ray emission spectra of cubic nitri des TaNx (NaCl structure, 0.81 less than or equal to x less than or eq ual to 1.172), hexagonal nitrides TaN0.99 (CoSn structure) and TaN0.90 (WC structure) have been derived and compared on a common energy scal e. In the sequence TaN (CoSn structure) --> TaN (WC structure) --> TaN (NaCl structure) a decrease of the N Ka band halfwidth was observed. In most substoichiometric cubic tantalum mononitrides with vacancies o n the metal sublattice (1.134 less than or equal to x less than or equ al to 1.172) a subband of non-bonding N 2p-like states appeared in the energy region between the Ta 5d-N 2p- and Ta 5d-like bands. In all ta ntalum nitrides studied the Ta Sd-like and N 2p-like states are strong ly hybridized, and a charge transfer occurs from Ta to N atoms.