Zintl phases for thermoelectric applications

Zintl phases have been recognized as an important class of materials that have good properties for thermoelectric applications. Zintl phases are intermetallic compounds that are semiconductors with complex structures and a mix of ionic and covalent bonding. These structure types are composed of elements that display ionic bonding or covalent bonding and can be tuned in multiple fashions to provide efficient thermoelectric materials. The covalent bonding provides unique 0D clusters, 1D chains, 2D layers, and 3D frameworks that are interspersed and valence satisfied with alkaline earth, alkali metal, or rare earth cations. Because both the anionic framework and the cations can be alio- or isovalently substituted, a vast array of new compounds can be synthesized, and precise tuning of properties can be achieved. The combination of both ionic and covalent bonding within a semiconducting structure makes this an ideal phonon-glass electron-crystal class of compounds. This chapter will outline some of the most recent successes for thermoelectrics and suggest directions for new endeavors.