Enhancement of p-type thermoelectric properties in an Mg2Sn system

In order to investigate the effect of both composition and the Ag-doping on the thermoelectric properties of Mg2Sn, samples with molar-ratio (Mg:Sn) range from 65:35 to 71:29 were synthesized using a vacuum melting process. For undoped specimens all the samples showed p-type characteristics at room temperature. As the temperature was increased, the Seebeck coefficients of all the samples were converted into n-type. The transition of the Seebeck coefficient from p- to n-type starts at lower temperatures for Mg-excess compositions than for Sn-excess compositions. Ag atoms were doped into the Mg2Sn in order to retain the p-type thermoelectric properties at high temperatures. The microstructures, as well as the thermoelectric properties, were also investigated. As a result, Ag-doping brought about a p-type power factor much higher than that for an undoped sample, especially for Sn-excess Mg2Sn compositions. The highest value of the figure of merit (0.18) was obtained from a 3-mol%Ag-doped Mg2Sn at 600 K, which resulted from the increase in the power factor and the decrease in lattice thermal conductivity.