Electronic structures of AgNi1-xCoxO2AgNi1-xCoxO2 delafossite oxides

Electronic structures of AgNi1-xCoxO2AgNi1-xCoxO2(0⩽x⩽1)(0⩽x⩽1) delafossite oxides have been investigated by using photoemission spectroscopy (PES) and soft X-ray absorption spectroscopy (XAS). T 2p XAS (T=CoT=Co, Ni) spectra of AgNi1-xCoxO2AgNi1-xCoxO2 show that the valence states of Co ions are trivalent and do not change with xx. In contrast, Ni ions are in the Ni2+–Ni3+Ni2+–Ni3+ mixed-valent states and the trivalent component increases with increasing xx. This finding suggests that the metallic nature of AgNi1-xCoxO2AgNi1-xCoxO2 for low values of xx arises from the divalent Ni ions. The valence-band PES study of AgNi1-xCoxO2AgNi1-xCoxO2 reveals that the Ni 3d states are more metallic like than the Co 3d states.