Besides our latest results on the optimization of the performances of Bi₂Te₃ near room temperature, this contribution will discuss the potential of Mg₃X₂ compounds. Mg₃Sb₂ and derived stoichiometries are highly promising materials for thermoelectric applications in mid temperature range (below 550K). Its importance stems from its exceptional thermoelectric performance, with figures of merit (ZT) exceeding 1.5 when alloyed with Bi (e.g., Mg₃Sb₂₋ₓBiₓ), placing it on par with or better than traditional materials like Bi₂Te₃. Mg₃Sb₂ combines low lattice thermal conductivity—due to strong phonon scattering from point defects and intrinsic lattice anharmonicity—with high carrier mobility, making it ideal for efficient heat-to-electricity conversion. The compound has a CaAl₂Si₂-type layered Zintl structure featuring covalently bonded [Mg₂Sb₂]²⁻ slabs separated by electropositive Mg²⁺ cations, enabling both structural anisotropy and phonon-glass/electron-crystal behavior. Furthermore, Mg₃Sb₂ is composed of abundant, low-cost, and non-toxic elements, making it attractive for scalable, environmentally benign energy technologies. Its transport properties can be finely tuned through doping (e.g., with Te, Se, or rare earth elements), and its defect chemistry allows for precise control of carrier concentration. Recent research has also demonstrated the impact of alloy disorder and band structure tuning on enhancing its performance. Overall, its unique combination of high efficiency, low cost, and chemical versatility makes Mg₃Sb₂ a leading material in the development of next-generation thermoelectrics. This presentation will show our latest results, especially the impact of metallic inclusion during and after the synthesis of the active matrix.

Franck Gascoin,  Professor of Rensselaer Polytechnic Institute.

After attending the University of Sciences and Techniques of Nantes, I received a M.S. in advanced solid state chemistry from the Institute Jean Rouxel.

In 1999 I 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, I obtained my Ph.D. degree for research on synthesis and characterization of pnictogen-based Zintl Phases.

Also In 2003, I joined the Thermoelectric Team of CALTECH – NASA Jet Propulsion Laboratory, where I 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 I was appointed as an assistant professor in Montpellier France, where I work in Jean Claude Tedenac’s team on new thermoelectric materials as well as on new innovative processing techniques.

In 2009, I moved to CRISMAT laboratory for my research activities and I joined the University of Caen Normandy as an assistant professor. I am 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.

I am now full professor of chemistry, I have led several large research projects and my involvement and my activities in thermoelectricity have been such that I have 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).