A Simple Chemical Guide for Finding Novel n-type Dopable Zintl Pnictide Thermoelectric Materials

Computations have predicted good thermoelectric performance for a number of Zintl phases when doped <i>n</i>-type. Combined with the successful experimental realization of <i>n</i>-type KGaSb<sub>4</sub>, KAlSb<sub>4</sub>, and Mg<sub>3</sub>Sb<sub>2</sub> with zT>1, this has fueled efforts to discover novel <i>n</i>-type dopable Zintl phases. However, a majority of Zintl phases exhibit strong proclivity toward <i>p</i>-type doping and prior successes in finding <i>n</i>-type dopable Zintls were largely serendipitous. Herein we use modern first-principles defect calculations to study trends in the dopability of Zintl pnictides and find that the average oxidation state of the anion is a useful chemical guide to identify novel <i>n</i>-type dopable phases. Specifically, we observe that Zintl pnictides with average oxidation of the anion near -1 are<i> n</i>-type dopable. The trend is mainly a consequence of the high formation energy of native acceptor defects (<i>e.g.</i> cation vacancies) and the resulting absence of charge (electron) compensation. Using the oxidation state guide in conjunction with a descriptor of thermoelectric performance, we conduct a large-scale materials search and identify promising candidates that are <i>n</i>-type dopable.