Doping effects on thermoelectric properties in the Mg 2Sn system

A weak point of Mg 2X thermoelectrics is the absence of a p-type composition, which motivates research into the Mg 2Sn system. Mg 2Sn thermoelectrics were fabricated by a vacuum melting method and a spark plasma sintering process. As a result, Mg 2Sn single phases were acquired in a wide range of Mg-to-Sn atomic ratios (67:33 to 71:29), showing slightly different thermoelectric characteristics. However, the thermoelectric properties of the undoped system were not sufficient for application in commercial production. To maximize the p-type characteristics, many atoms [Ni (VIIIA), Cu (IB), Ag (IB), Zn (IIB), and In (IIIB)] were doped into the Mg 2Sn phase. Among them, the power factor values increased only in the Ag-doped case. Ag-doping resulted in a power factor that was more than 10 times larger than the value in the undoped case. This result could be important for developing p-type polycrystalline thermoelectrics in the Mg 2X (X = Si, Sn) system. However, other atoms [Ni (VIIIA), Cu (IB), Zn (IIB), and In (IIIB)] were not determined to act as acceptor atoms. The maximum ZT value for the Ag-doped Mg 2Sn thermoelectric was more than 0.18, which is comparable to the value for the n-type Mg 2Si system. © 2012 TMS.