Advancing Nontoxic, Antimony-based 1–2–2-type Thermoelectric Zintls
We contributed to the advances of nontoxic, antimony-based 1–2–2-type Zintl thermoelectric materials from three aspects. Firstly, p-type CaMg2Sb2 has not been favorably considered a promising thermoelectric material in comparison to other Zintl phases. However, a series of meticulously designed tactics is successfully implemented here to analyze and improve the thermoelectric performance of a CaMg2Sb2-based material. As a result, a 20-fold-higher peak zT of ~0.85 at 773 K and an average zT value of ~0.50 from 298 K to 773 K are achieved, both values among the highest reported for strictly AMg2Sb2-based (A = Ca, Mg, Eu, Yb, or any combination thereof) materials reported to date. Secondly, contrary to the similar thermoelectric performance among both AZn2Sb2 and AMg2Bi2 compounds, their isostructural counterparts, AMg2Sb2, can exhibit thermoelectric figure of merit values that vary by orders of magnitude with different A elements. Here, we reveal physical origins accounting for the significantly differing performance among AMg2Sb2-based compounds (A = Ca, Sr, Sm, Yb, and Mg) through exhaustive analyses, where it is shown that the disparities in performance at the macroscale essentially originate from the widely varying activation energies that equal amounts of dopant can induce. Meanwhile, a few unusual transport behaviors regarding electrical conductivity, carrier concentration, or lattice thermal conductivity among these compounds have been identified, and we also present their rationales in depth. Thirdly, we conceived a new method to design a series of 1–2–2-type Zintl compositions with an effect beneficial to thermoelectric performance at one time, which will be elaborated in the main text of this dissertation. This dissertation showcases a full-scale advancement of nontoxic, antimony-based 1–2–2-type thermoelectric Zintls from fundamentals to applications.
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