CHARACTERIZATION OF NONSTOICHIOMETRIC NICKEL-OXIDE THIN-FILM ELECTRODES

Thin-film nonstoichiometric nickel oxide is an interesting intercalation electrode with unique electrochemical and optical properties which can be successfully used for improved electrochromic displays and windows of relevant technological interest. However, the correlation between the intercalation process of lithium and the modifications of the physical properties of the host oxide are not yet fully understood. We attempt here to demonstrate that these modifications may be interpreted conveniently on the basis of a small polaron model. The results confirm that a model of this type can account for the observed electrochemical and electrochromic response of the nickel oxide electrode as a function of the injected charge, Q(Li). The model assumes that on charging the nickel oxide changes progressively from a degenerated metallike p-type semiconductor in the pristine state to a p-type semiconductor in the low intercalated state (i.e., for Q(Li) < 140 mC cm-2 mum-1), then to an n-type semiconductor in the high intercalated state (i.e., for Q(Li) > 140 mC cm-2 mum-1), and again to a degenerated, metallike material in the full intercalated state (i.e., for Q(Li) >> 140 mC cm 2 mum-1).