High performance of eco-friendly magnesium system thermoelectric material by the controlled defect and composition.

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Mg_2SiSn system thermoelectric semiconductor, which introduced the schottky defect or the Fraenkel defect, changed the conduction type by those defects. Those causes were 1) an electron as a donor was produced by the Fraenkel defect of Mg atom, 2) a hole as an acceptor was produced by the schottky defect of the interstitial Mg atom.The electron concentration of Mg2SiSn with the grain boundary defect was decreased remarkably, this is, the electronic trap-level was formed by the grain boundary defect. Therefore, a hole became dominant and p-type conduction was shown.The controlling of carrier concentration by these defects was possible.The performance of p-type Mg2SiSn by the controlling of defect and composition was improved about 3 times.