Xanes study and valence states in (R1, R2-DCNQI)2Cu

Abstract

XANES (X-ray Absorption Near Edge Structure) measurement at Cu K-edge is reported in (R1, R2-DCNQI)2Cu (R1, R2 = CH3, CH3O, Cl, Br). The valence states of Cu are examined using XANES spectra. The arguments in the valence state using XPS (X-ray Photoelectron Spectroscopy) are reconsidered. XANES spectroscopy can give intrinsic information because it is bulk sensitive in contrast to the XPS which is surface sensitive. The two groups in DCNQI-Cu family are examined, and it is confirmed that the difference in the spectra exists between two groups. We observed clear change of valence state in group II materials which show metal-insulater(M-I) transition, where the Cu2+ contribution clearly increases below M-I transition temperature. Therefore it is confirmed that the Cu-site is related to the transport property. On the other hand we have seen no marked change in valence for group I materials which are metallic down to low temperatures. And the Cu2+ contribution at room temperature is markedly smaller than that of group II. The valence mixing extents are different between group I and group II even at room temperature.