Recent predictions highlight that the exponential increase of computational operation could present a major share of energy consumption by 2050. To overcome this problem, new and energy efficient computing elements and logics must be developed. The possibility of changing the properties of materials by voltage-driven ion migration represents a promising approach to reach ultralow-power in storage and computing devices. An excellent example of the modulability of functional properties can be found in hole-doped perovskite ferrites, La_1-xSr_xFeO_3-δ (LSF) thin films. Control on their properties is usually achieved either by A-side doping (x) or change of the oxygen vacancy concentration (δ) ^{[1, 2]}. In order for these materials to be implemented in next-generation devices, however, a detailed understanding and control of the underlying mechanisms controlling the stoichiometry-functionality relationship is of outmost importance.

In this work, we present the tuning of the oxygen vacancy concentration δ as a powerful tool for the careful control of electrical conductivity and related properties in the La_1-xSr_xFeO_3-δ  (LSF) family. This effect is achieved by voltage-driven (de)intercalation of oxygen ions in a robust, fast, and reversible way in highly oriented LSF films deposited on a solid electrolyte. Two exemplary materials in this family were chosen for a comparative study: SFO (SrFeO_3-δ) and LSF50 (La_0.5Sr_0.5FeO_3-δ). We show that potentially infinite intermediate states, characterized by different electronic conductivity, can be stabilized by changing the oxygen content in a continuous and controlled way (from a conductivity of 10^-3Scm^-1 to an increase of up to 5 orders of magnitude for both LSF50 and SFO measured at 50°C, and a measurable change as low as 2·10^-3Scm^-1). This holds true for both SFO – which presents a metal-to-insulator transition based on its topotactic transformation from a perovskite to a stabilized brownmillerite depending on δ – but also for LSF, i.e. within the single-phase domain. This represents a remarkable step forward with respect to the state of the art, where for example SFO is usually treated as a simple binary system, and make the SFO-LSF family a potential candidate e.g. for optical-based devices and analog memories. A smart experimental design allowed for the simultaneous characterization of structural, optical, electrical, and magnetic properties of the films, shedding light on the mechanisms that correlate such properties with the oxygen content and temperature. These results reveal clear trends that can serve as a guide for the implementation of future devices based on the LSF group materials.