Recent progress and future challenges on thermoelectric Zintl materials

Thermoelectric materials have attracted extensive interest in the last two decades due to their potential applications in waste-heat recovery from industrial processes, automobiles, and renewable energy sources. Among the various candidate materials, Zintls have recently gained significant interest because of their high thermoelectric figure of merit (ZT) for potential use in thermoelectric power generation. In this review, we first briefly summarize some of the most intensely studied Zintl families with unique and diverse anionic frameworks, ranging from isolated moieties to one-dimensional (1D) chains of tetrahedra or frames of ribbons to 2D layered structures, along with discussion of their challenges and possibilities for further improvements. Second, the 2D layered CaAl2Si2-type Zintl phases are discussed in more detail, from fundamental crystal structure and electronic band structure to the approaches that have been successfully used to enhance the thermoelectric performance. Finally, we provide an overview of the recent progress in thermoelectric Zintl materials, particularly the most recent exciting development in achieving high ZTs in n-type Zintls, and what can be realistically expected for advancing this class of materials into practical applications. (c) 2017 Published by Elsevier Ltd.