XPS studies of the intermediate valence state of Yb in (YbS)1.25CrS2

This paper presents clear evidences for valence fluctuation of Yb in (YbS)(1.25)CrS2. The X-ray photoelectron spectroscopy (XPS) spectra of Yb 4f, 5p, 4d and 4p have been measured. They reveal the multiplet structures of Yb2+ and Yb3+, indicating that it is a homogeneous mixed-valence misfit-layer compound like (EuS)(1.173)NbS2 while keeping non-metallic properties. Yb 4f, 4d and 4p spectra are deconvoluted into the components of Yb2+ and Yb3+, from the relative areal intensities of which an intermediate valence has been estimated to be 2.89 in average. This result indicates that about 1.11 electrons per chemical formula are transferred from a YbS layer. On the other hand, the Cr 2p spectrum shows the spin-orbit (s.o.)-split peaks of Cr3+, implying that an electron per Cr is transferred to a CrS2 layer. An apparent contradiction in the transferred electrons may arise from metal deficiency within a YbS layer. (C0 2008 Elsevier B.V. All rights reserved.