Optimization of thermoelectric properties of n-type Mn- and Te-doped Mg3Sb2-x Bi x phases

This study explores the effects of Mg and Bi amounts, ball milling duration, and sintering conditions on the purity and thermoelectric properties of the Mn- and Te-doped Mg3Sb2-x Bi x phases (Mg2.97+y Mn0.03Bi x Sb1.99-x Te0.01). We found that excess Mg is necessary to achieve phase pure samples, but too much Mg forms impurities that decrease thermoelectric efficiency. Increasing Bi content leads to lower phase stability and decomposition. There is also an optimal ball milling time, beyond which decomposition of the material occurs. The highest figure of merit, zT, of 1.44 was achieved for the Mg3.27Mn0.03Bi1.30Sb0.69Te0.01 sample at 623K, which is comparable to the performance of Bi2Te3. Our findings suggest that Mg3Sb2-x Bi x phases are promising low-cost and environmentally friendly thermoelectric materials mid-range temperature applications.