Contrary to traditional approaches, high entropy oxides (HEOs) strategically employ cationic disorder to engineer tunable functionalities. This disorder, stemming from multiple elements at the same crystallographic site, disrupts local symmetry and induces local distortions. By investigating a series of single-crystalline $[{\mathrm{La}}_{0.2}{\mathrm{Pr}}_{0.2}{\mathrm{Nd}}_{0.2}{\mathrm{Sm}}_{0.2}{\mathrm{Eu}}_{0.2}{]\mathrm{NiO}}_{3-\delta }$ thin films, grown by pulsed laser deposition, we demonstrate herein that the creation of oxygen vacancies (OVs) further offers a powerful means of tailoring electronic behavior of HEOs by concurrently introducing disorder and doping electrons into the system. Increasing OV concentration via changing the oxygen partial pressure during the ablation leads to a monotonic increase in room-temperature sheet resistance. A striking feature is the Janus-faced response of the metal-insulator transition (MIT) due to the interplay among correlation energy scales, electron doping, and disorder. Unlike the monotonous influence of OV observed for the MIT in ${\mathrm{VO}}_2$ and ${\mathrm{V}}_2{\mathrm{O}}_3$, initial OV doping lowers the MIT temperature here, whereas higher OV levels completely suppress the metallic phase. Magnetotransport measurements further reveal weak localization, and strong localization as a function of relative change in $\delta$. Moreover, the disorder on both $RE$ and oxygen sublattices is responsible for the Mott-Anderson insulator state. These findings surpass the scope of the recently featured “electron antidoping” effect.

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• Electronic structure
• Oxides
• Thin films
• Physical deposition
• Resistivity measurements
• X-ray absorption spectroscopy