Oxygen Vacancy Defect Engineering for Transverse Thermoelectric Enhancement: a Novel Extrinsic Pathway beyond Intrinsic Approaches

For efficient transverse thermoelectric (TE) generation, research has primarily focused on achieving high transverse TE conductivity by utilizing intrinsic material properties. While this approach remains fundamental, exploring extrinsic strategies, such as defect engineering, offers new opportunities to further enhance performance and expand the range of applicable materials. This study investigates the impact of oxygen vacancies-an extrinsic factor-on the anomalous Nernst effect, a key transverse TE mechanism, using disordered semiconducting Sr₃YCo₄O_11- _δ (δ = 0.02, 0.08 and 0.14) as a model system. The highest anomalous Nernst thermopower (S_ANE) occurs at δ = 0.14, showing a 44% increase compared to δ = 0.02. This enhancement arises from two synergistic effects: i) increased Co³⁺/Co⁴⁺ mixed valency, boosting entropy-driven charge transport and Seebeck thermopower, and ii) distortions in the Co-O-Co bond angle, elevating the local density of states and the anomalous Nernst angle. These findings establish oxygen vacancy defect engineering as a potent strategy for enhancing transverse TE performance, broadening the spectrum of viable TE materials for diverse engineering applications.