Electronic structures of AgNi1-xCoxO2 delafossite oxides

Electronic structures of AgNi1-xCoxO2 (0 <= x <= 1) delafossite oxides have been investigated by using photoemission spectroscopy (PES) and soft X-ray absorption spectroscopy (XAS). T 2p XAS (T = Co, Ni) spectra of AgNi1-xCoxO2 show that the valence states of Co ions are trivalent and do not change with x. In contrast, Ni ions are in the Ni2+-Ni3+ mixed-valent states and the trivalent component increases with increasing x. This finding suggests that the metallic nature of AgNi1-xCoxO2 for low values of x arises from the divalent Ni ions. The valence-band PES study of AgNi1-xCoxO2 reveals that the Ni 3d states are more metallic like than the Co 3d states. (c) 2006 Elsevier B.V. All rights reserved.