Promoted application potential of p-type Mg3Sb1.5Bi0.5 for the matched thermal expansion with its n-type counterpart

Recently, n-type Mg3Sb1.5Bi0.5-based thermoelectric materials have attracted considerable attention for their extraordinary thermoelectric performance. Ideally, thermoelectric generators should be made of the same material system to avoid thermal mismatch in the practical application. In this work, p-type Mg3Sb1.5Bi0.5 which has almost the same composition as the state-of-the-art n-type Mg3.2Sb1.5Bi0.49Te0.01Mn0.01 was synthesized by ball milling and spark plasma sintering, and then Na was chosen as an acceptor dopant to optimize the carrier concentration and further improve the thermoelectric performance. Na0.0075Mg2.9925Sb1.5Bi0.5 sample gets the highest ZT of ∼0.5 at 773 K. While Na0.005Mg2.995Sb1.5Bi0.5 sample shows the highest average ZT of ∼0.29 in the temperature range of 300–773 K and matched thermal expansion behavior with the state-of-the-art n-type Mg3.2Sb1.5Bi0.49Te0.01Mn0.01, which is of great significance for practical applications. Taking the Joule and Thompson heat into account, a high theoretical conversion efficiency (η) of ∼9.5% was calculated for the thermoelectric module consists of the present p-type Na0.005Mg2.995Sb1.5Bi0.5 and the state-of-the-art n-type Mg3.2Sb1.5Bi0.49Te0.01Mn0.01 with the leg length of 2 mm, and cold and hot side temperature of 300 K and 773 K, respectively, which shows a good potential for the use of this class of materials in the mid-temperature power generation applications.