Novel synthesis recipes boosting thermoelectric study of A₂Q (A  =  Cu, Ag; Q  =  S, Se, Te)

Discovering new materials and developing novel synthesis techniques are like two wheels of a cart in materials-based science and technology. As is often the case, innovative synthesis recipe can rejuvenate the research landscape of a material that is otherwise thought to be matured. A good example of such is the narrow band gap semiconductor/semimetal family of A₂Q (A  =  Cu, Ag; Q  =  S, Se, Te). Here we briefly review the recent development of synthesis recipes and the impact on the thermoelectric study of A₂Q. While the mixed ionic electronic conduction in A₂Q promises advantages in thermoelectricity, it poses challenges in material synthesis and applications. The concepts, approaches, and strategies embodied in these novel synthesis recipes of A₂Q can be extended to other materials in diverse regimes of fundamental research and technical applications beyond thermoelectrics. (topical review)