The thermoelectric performance of Mg3+xSb1.5Bi0.49Te0.01 was improved by reducing the amount of excess Mg (x = 0.01-0.2). A 20% reduction in effective lattice thermal conductivity at 600 K was observed by decreasing the nominal x from 0.2 to 0.01 in Mg3+xSb1.5Bi0.49Te0.01, leading to a 20% improvement in the figure-of-merit zT. Since materials with different amounts of Mg have similar electronic properties, the enhancement is attributed primarily to the reduction in thermal conductivity. It is known that excess Mg is required to make n-type Mg3+xSb1.5Bi0.49Te0.01; however, too much excess Mg in the material increases the thermal conductivity and is therefore detrimental for the overall thermoelectric performance of the material.
