CAREER: Overcoming the trade-off between thermopower and conductivity in transition metal oxides

University Of South Carolina At Columbia, Columbia SC

Investigators

Abstract

Nontechnical Description Nearly two-thirds of the total energy generated by humanity is wasted as heat. In the face of growing concerns about climate change, efficient recycling of waste heat is an urgent significant scientific challenge. The thermoelectric (TE) conversion process transforms waste heat into usable electric power, providing a promising source of clean and sustainable energy. The efficiency of this process depends on the intrinsic properties of materials, particularly thermopower and electrical conductivity. Yet, current oxide material systems and engineering designs face challenges in achieving favorable TE properties. The discovery of new materials with good TE properties and designs to take advantage of them is therefore crucial for the development of high-performance TE devices. This project focuses on transition metal oxides, which are promising TE materials due to their non-toxic nature, abundance, and stability at high temperatures. This project aims to establish a novel approach for achieving large thermopower and high conductivity in transition metal oxides. This approach combines a new oxide heterostructure with columnar microstructures and vertical interfaces, along with the addition of metal nanoparticles. The PI is committed to elevating public awareness of the pivotal role of materials science and fostering the growth of future materials scientists and engineers. Towards this end, the PI plans to provide lectures and science demonstrations on oxides to high school students and teachers. Furthermore, hands-on research training and mentorship opportunities are provided for underrepresented undergraduate and graduate students to spark interest in materials science engineering studies and related careers. Technical Description To meet the growing demand for high-temperature TE devices capable of converting waste heat into electricity, it is indispensable to discover transition metal oxides (TMOs) with large thermopower and high electrical conductivity, enabling a substantial power factor. Nevertheless, due to the inherent trade-off relationship between enhancing conductivity and thermopower, achieving TMOs with simultaneously high values of both properties remains a formidable challenge. The overarching goal of this project is to overcome this trade-off by establishing a completely new approach that combines two emerging strategies: vertical strain and the unique redox defect chemistry of TMOs. The PI plans to explore the relationships between strain, redox defects, and TE properties in TMOs by synthesizing vertically aligned nanocomposites composed of two different perovskites through pulsed laser deposition in combination with the exsolution of metal nanoparticles. In perovskite materials with A-site deficiencies, metal exsolution occurs during reduction, leading to an energy filtering effect that enhances thermopower while preserving conductivity with minimal deterioration. Simultaneously, by maximizing tensile strain along the vertical interface in vertically aligned nanocomposites, the concentration of oxygen vacancies in electron-doped perovskites significantly increases, leading to an enhancement of conductivity. The fundamental knowledge gained on the relationships between strain, redox defects, and TE properties in this project provides unprecedented design freedom and facilitates the development of oxide TE materials with superior properties. In addition, this project benefits from the use of cutting-edge techniques in national laboratory user facilities, enhancing the precision and depth of the investigations. The innovative approach in this project can serve as a versatile architecture capable of accommodating a diverse array of functional properties, leading to advancements in a wide range of energy and electronic applications, ultimately benefiting the public. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.