Phase Boundary Mapping of Tin‐Doped ZnSb Reveals Thermodynamic Route to High Thermoelectric Efficiency

Abstract The thermoelectric material ZnSb utilizes elements that are inexpensive, abundant, and viable for mass production. While a high thermoelectric figure of merit zT, is difficult to achieve in Sn‐doped ZnSb, it is shown that this obstacle is primarily due to shortcomings in reaching high enough carrier concentrations. Sn‐doped samples prepared in different equilibrium phase spaces in the ternary Zn‐Sb‐Sn system are investigated using phase boundary mapping, and a range of achievable carrier concentrations is found in the doped samples. The sample with the highest zT in this study, which is obtained with a carrier concentration of 2 × 10¹⁹ cm⁻³ when the material is in equilibrium with Zn₄Sb₃ and Sn, confirms that the doping efficiency can be controlled by preparing the doped sample in a particular region of the thermodynamic phase diagram. Moreover, density functional theory calculations suggest that the doping efficiency is limited by the solubility of Sn in ZnSb, as opposed to compensation from native defects. Cognizance of thermodynamic conditions is therefore crucial for rationally tuning the carrier concentration, a quantity that is significant for many areas of semiconductor technologies.