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 has been studied by X-ray and ultraviolet photoelectron spectroscopy and by LMTO band structure calculations. Improved methods for the synthesis of several of the materials are described. The electronic structure of compounds with discrete clusters (Na22Ba14SrN6) or Ba3N chains (Ba3N, NaBa3N, Na5Ba3N) in the crystal structure 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 ionic bonding between N3- ions and surrounding partly oxidized alkaline earth metal atoms. The N-2p regions in valence band spectra and density-of-states curves of Ca2N, Sr2N and 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 spectra 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 electrons from the metal valence band or from N-2p levels. (C) 1998 Elsevier Science Ltd. All rights reservedThe electronic structure of various alkaline earth metal subnitrides has been studied by X-ray and ultraviolet photoelectron spectroscopy and by LMTO band structure calculations. Improved methods for the synthesis of several of the materials are described. The electronic structure of compounds with discrete clusters (Na22Ba14SrN6) or Ba3N chains (Ba3N, NaBa3N, Na5Ba3N) in the crystal structure 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 ionic bonding between N3- ions and surrounding partly oxidized alkaline earth metal atoms. The N-2p regions in valence band spectra and density-of-states curves of Ca2N, Sr2N and 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 HeI, NeII and HeII spectra 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 electrons from the metal valence band or from N-2p levels. (C) 1998 Elsevier Science Ltd. All rights reserved.