Oxide-based valence-change memristors are promising nonvolatile memories for future electronics that operate on valence-change reactions to modulate their electrical resistance. The memristance is associated with the movement of oxygen ionic carriers through oxygen vacancies at high electric field strength via structural defect modifications that are still poorly understood. This study employs a Ce1-xGdxO2-y solid solution model to probe the role of oxygen vacancies either set as "free" or as "immobile and clustered" for the resistive switching performance. The experiments, together with the defect chemical model, show that when the vacancies are set as "free", a maximum in memristance is found for 20 mol % of GdO1.5 doping, which clearly coincides with the maximum in ionic conductivity. In contrast, for higher gadolinia concentration, the oxide exhibits only minor memristance, which originates from the decrease in structural symmetry, leading to the formation of "immobile" oxygen defect clusters, thereby reducing the density of mobile ionic carriers available for resistive switching. The research demonstrates guidelines for engineering of the oxide's solid solution series to set the configuration of its oxygen vacancy defects and their mobility to tune the resistive switching for nonvolatile memory and logic applications.
Keywords: Raman; ceria; memristor; oxygen vacancies; resistive switching.