ELECTRONIC-STRUCTURE AND CHEMICAL BONDING IN ALKALINE-EARTH METAL SUBNITRIDES - PHOTOEMISSION-STUDIES AND BAND-STRUCTURE CALCULATIONS

The electronic structure of various alkaline earth metal subnitrides h as been studied by X-ray and ultraviolet photoelectron spectroscopy an d by LMTO band structure calculations. Improved methods for the synthe sis of several of the materials are described. The electronic structur e of compounds with discrete clusters (Na22Ba14SrN6) or Ba3N chains (B a3N, NaBa3N, Na5Ba3N) in the crystal structure is characterized by a n arrow atomic-like N-2p band occurring between 2 and 2.5 eV in the phot oemission spectra. The spectra and the results from the band structure calculations support the idea of ionic bonding between N3- ions and s urrounding partly oxidized alkaline earth metal atoms. The N-2p region s in valence band spectra and density-of-states curves of Ca2N, Sr2N a nd Ba2N, which have layered crystal structures, extend over a broader energy range, suggesting a more pronounced dispersion of the N-2p band in these compounds. Several feature seen in NeI Hel, NeII and HeII sp ectra of the series M2N are assigned to Anger transitions involving a primary hole in a shallow core level (N-2s or M-np) and either electro ns from the metal valence band or from N-2p levels. (C) 1998 Elsevier Science Ltd. All rights reservedThe electronic structure of various al kaline earth metal subnitrides has been studied by X-ray and ultraviol et photoelectron spectroscopy and by LMTO band structure calculations. Improved methods for the synthesis of several of the materials are de scribed. The electronic structure of compounds with discrete clusters (Na22Ba14SrN6) or Ba3N chains (Ba3N, NaBa3N, Na5Ba3N) in the crystal s tructure is characterized by a narrow atomic-like N-2p band occurring between 2 and 2.5 eV in the photoemission spectra. The spectra and the results from the band structure calculations support the idea of ioni c bonding between N3- ions and surrounding partly oxidized alkaline ea rth metal atoms. The N-2p regions in valence band spectra and density- of-states curves of Ca2N, Sr2N and Ba2N, which have layered crystal st ructures, extend over a broader energy range, suggesting a more pronou nced dispersion of the N-2p band in these compounds. Several feature s een in NeI HeI, NeII and HeII spectra of the series M2N are assigned t o Anger transitions involving a primary hole in a shallow core level ( N-2s or M-np) and either electrons from the metal valence band or from N-2p levels. (C) 1998 Elsevier Science Ltd. All rights reserved.