Preparation and characterization of NaInO2 and NaInS2

NaInO2 and NaInS2 with alpha-NaFeO2 layer type structure have been prepared and characterized by X-ray photoelectron spectroscopy to clarify the role of the anions in the electronic structures of the compounds. The In 3d(5/2) binding energy for both compounds was the same, though the Na 1s binding e nergy of NaInO2 was larger than that of NaInS2 by 0.4 eV. The change in the Na Auger parameter, defined as the sum of Na 1s binding energy and KLL Aug er kinetic energy, suggests that the difference in extra-atomic relaxation energy between the compounds causes the Na 1s binding energy shift. Discret e variational-X alpha model cluster calculations for NaInO2 and NaInS2 mirr ored the experimental valence band spectra and the difference of 0.5 eV in optical absorption energy of the compounds. The cluster calculation reveale d that in NaInO2 the highest occupied level is formed by an antibonding Na- O bond, whereas that in NaInS2 is formed by a bonding Na-S bond. The covale nt Na-S bond decreases the extra-atomic relaxation energy for Na 1s electro n emission from NaInS2.