CAREER: Heteroanionicity by Design: Developing Complex Narrow-Bandgap Oxypnictide Semiconducting Materials for Thermoelectric Applications

PART 1. NON-TECHNICAL SUMMARY

The development of novel, efficient functional materials for energy applications is essential for addressing global energy challenges, promoting sustainability, and driving economic growth. With this project, supported by the Solid State and Materials Chemistry Program in the Division of Materials Research, the Prof. Baranets and his research group at Louisiana State University design and create new semiconducting materials with potential for thermoelectric applications - specifically, converting waste heat into electricity.

The researchers focus on a unique class of compounds known as charge-balanced heteroanionic oxypnictides. These materials incorporate multiple anionic (negatively charged) species, such as oxides and pnictides (e.g. phosphorus, arsenic, antimony, bismuth), with different ionic sizes and charges into their crystal structures. This approach enhances compositional and structural diversity, functionality, tunability of properties, such as thermoelectric performance.

By integrating experimental techniques and computational tools, the research project uncovers the rational principles underpinning the targeted design of heteroanionic compounds, discovers novel semiconductors with unique atomic arrangements and functionality, and paves the way for advanced materials with enhanced thermoelectric efficiency. In addition, this research addresses the national need to improve STEM education.

It offers mentorship and interdisciplinary training opportunities for graduate and undergraduate students, equipping them with skills critical to addressing future energy and technology challenges. This project actively engages students from diverse backgrounds in hands-on research, enhances learning via cutting-edge virtual reality tools, and fosters collaboration with local high schools to improve chemistry education through coaching sessions for the US National Chemistry Olympiad K-12 students and workshops for local high-school teachers.

PART 2: TECHNICAL SUMMARY

The primary objective of this project is to establish rational principles for the strategic synthesis and design of novel multinary Zintl-like heteroanionic oxypnictide semiconductors with narrow band gaps. These materials, featuring separated pnictide, Pn3− (Pn = P, As, Sb, Bi), and oxide, O2−, anions, exhibit significant potential for high- and mid-temperature range thermoelectric applications.

Narrow-gap Zintl semiconductors are particularly promising due to their desirable combination of tunable transport properties (e.g., Seebeck coefficient, electrical and thermal conductivity, charge carrier concentration), making them ideal candidates for thermoelectric applications. Heteroanionic oxypnictides possess extraordinarily rich and complex structural chemistry due to the presence of multiple anions with varied ionic sizes, charges, and coordination environments.

This complexity facilitates the tunability of transport properties through a balance of ionic and covalent bonding, characteristic of Zintl phases. By leveraging this structural versatility, the principal investigator and his research group investigate novel functional materials. The research integrates (i) a blend of traditional and modern approaches to solid-state synthesis; (ii) predictive methodologies, such as empirical Zintl counting, structural relationships, and comprehensive high-throughput computational discovery coupled with electronic structure analysis; (iii) a fundamental understanding of the impact of anion ordering effects on structure-property correlations and suitability of Zintl oxypnictides for narrow-gap semiconducting applications; and (iv) development of traditional (band engineering, doping) and non-traditional (high-pressure) tunability approaches to investigate thermoelectric properties.

This project advances the landscape of novel compositions and structures, developes a broader understanding of heteroanionic materials chemistry, but also establishes foundational design principles for the potential development of high-performance thermoelectric materials. These efforts promote the discovery of unique and attractive chemical and physical properties and innovative applications.

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.