Vacancy-Induced Semiconductor–Insulator–Metal Transitions in Nonstoichiometric Nickel and Tungsten Oxides

Metal–insulator transitions in strongly correlated oxides induced by electrochemical charging have been attributed to formation of vacancy defects. However, the role of native defects in affecting these transitions is not clear. Here, we report a new type of phase transition in p-type, nonstoichiometric nickel oxide involving a semiconductor-to-insulator-to-metal transition along with the complete reversal of conductivity from p- to n-type at...