Over the last few decades, the blooming interest on n‐type Mg 3 Sb 2 ‐based alloys in the room‐temperature regime is of utmost importance owing to its properties capable of replacing the widely studied as well as commercialized Bi 2 Te 3 ‐based alloys. This alternate hunt is to overcome the dependency on the one of the rarest elements on earth's crust, i.e., Te. In this regard, an in‐depth understanding of the role of dopants to achieve n‐type conduction is paramount significance as the aforementioned alloy in stoichiometric amount is highly vulnerable toward p‐type conduction with extremely low carrier concentration owing to the loss of Mg during the synthetic step. To avert the situation, over stoichiometric state of Mg is crucial; however, an arbitrary increase in the Mg content may lead to the undesired phase and subsequently the chemistry of the alloy may differ. The present study unleashes the two chemical conditions for economically efficient room‐temperature‐based n‐type Mg 3 Sb 2 alloy, viz. (i) cationic self‐doping in the presence of anionic external dopant and (ii) cationic self‐doping and external doping in the absence of anionic dopant. Extensive investigation unveils that Mg‐rich condition is the prerequisite condition for n‐type conduction; however, the addition of excess Mg should be within the solubility—limit of Mg in the presence of Te. Thus, a systematic and detailed experiment was carried out to arrive at the solubility limit of Mg in Mg 3 Sb 2 ‐based alloys for enhanced thermoelectric performance. Nonetheless, to forestall the problems associated with excess Mg, cationic substitution with group‐3 elements was carried out. However, the study divulges that the ionic radii of the dopants are crucial for effective n‐type dopant. Here, the concentrations of yttrium under study is found to be an effective cationic dopant under Mg‐rich condition, whereas indium with ionic radii comparable to that of Mg both in four‐ and six‐coordinate geometries showed that it can substitute both Mg (1) and Mg (2) along with Sb site under Mg‐rich condition and eventually cause electron compensation defect. Surprisingly, In Mg(1) being acceptor defect and In Sb being electron compensation defect cause p‐type conduction in Mg 3 Sb 2 and thus not effective for high performance considering the concentrations under study. Among all the compositions studied, Mg 3.2 Sb 1.49 Bi 0.49 Te 0.02 was found to exhibit a peak ZT of 1.7 at 623 K (350°C). However, we have considered Mg 3.3 Sb 1.49 Bi 0.49 Te 0.02 to be more suitable from device viewpoint owing to have appreciably good average ZT .
Mohanty et al. (Sun,) studied this question.