Photoelectron spectra and surface valence fluctuation of Eu in the misfit-layer compound {(EuS) 1.15} 1.5NbS 2

Abstract

The 1.5Q/1 H type of the misfit layer compound {(EuS) 1.15} 1.5NbS 2 has been studied by X-ray photoelectron spectroscopy. Eu 3d, 4d, 4f and 5p spectra are measured with Al and MgKα radiation. Their intensities are analyzed, taking the escape depth of photoelectrons emitted from the core levels into account. The results indicate that valence transfer of nearly-half Eu 2+ ions to Eu 3+ happens in the outermost surface layer and a reduced Eu–S distance brings about surface rearrangement. It is confirmed that Eu 2+ and Eu 3+ coexist in a bulk, in consistency with bond valence calculations and Mössbauer spectra. The XPS spectra are well interpreted in terms of the multiplet structures of Eu 2+ and Eu 3+.