Polar intermetallics: Fundamentals and Opportunities for Thermoelectric Materials
Guest Speaker：Prof. Franck GASCOIN, University of Caen Normandy, France
Inviter: Prof. Tianran Wei
Date&Time: Wednesday, 22 April, 15:00-17:00
Venue: Room 2000A/B, Xu Zuyao Building
Biography:
Dr. Franck GASCOIN is now full professor of chemistry in the University of Caen Normandy, France. After attending the University of Sciences and Techniques of Nantes, he received a M.S. in advanced solid-state chemistry from the Institute Jean Rouxel. In 1999, he entered the graduate school of Notre Dame University (Indiana, USA) and joined Prof. S.C. Sevov’s group performing “hard core” solid state chemistry. In 2003, He obtained his Ph.D. degree for research on synthesis and characterization of pnictogen-based Zintl Phases. Also in 2003, he joined the Thermoelectric Team of CALTECH – NASA Jet Propulsion Laboratory, where he worked on high temperature thermoelectric materials within the framework of the Segmented Thermoelectric Multicouple Converters NASA program with mentors like Jeff Snyder and Thierry Caillat. Two years later he was appointed as an assistant professor in Montpellier France, where He work in Jean Claude Tedenac’s team on new thermoelectric materials as well as on new innovative processing techniques. In 2009, he moved to CRISMAT laboratory for his research activities and he joined the University of Caen Normandy as an assistant professor. He was leading research on thermoelectric materials form exploratory research of new compounds to optimization of known thermoelectric materials through various methods including microwave synthesis and sintering, SPS reactive sintering, microstructure engineering, composites etc.
He has led several large research projects and actively involved in the community of thermoelectrics. He has been elected in the board of the International Thermoelectric Society in 2013, served as secretary and eventually became the President of the International thermoelectric society (2018-2023).
Abstract:
Polar intermetallics occupy a unique position at the crossroads of solid-state chemistry, electronic structure, and materials design. Built upon valence-precise combinations of electropositive cations and polyanionic frameworks, these compounds bridge ionic and covalent bonding regimes, offering an exceptional playground to understand how structure dictates electronic properties. This talk will introduce the foundational concepts that define Zintl chemistry—electron counting rules, cation–anion electron transfer, bonding motifs ranging from chains to complex 3D networks, and the structural flexibility that arises from these principles. Building on these fundamentals, we will explore why Zintl phases have emerged as a privileged class of thermoelectric materials. Their intrinsically low lattice thermal conductivity, tunable carrier concentrations, and rich structural chemistry allow simultaneous control of electrical and thermal transport—key ingredients for high performance. Examples from classic and emerging systems will illustrate strategies for optimizing thermoelectric efficiency, including band engineering, alloying, defect design, and the exploitation of complex or anharmonic frameworks. By the end of the presentation, attendees will gain a clear understanding of how Zintl concepts guide the discovery of new compounds, deepen our insight into structure–property relationships, and open avenues for the development of next-generation energy conversion materials. Specifically, I will exemplify the potential of Zintl phases as thermoelectric materials with the compounds Yb14MnSb11, CaZn2Sb2 and Mg3(Sb,Bi)2 amongst others.