Thermoelectric properties of Sb-doped Mg2(Si0.95Ge0.05) synthesized by spark plasma sintering

• We have studied influence of Sb-doping and Ge-doping for thermoelectric properties of Mg2Si.
• Mg2Si and Sb doped Mg2(Si0.95Ge0.05) were synthesized using spark plasma sintering equipment.
• The Mg2Si samples were analyzed by XRF, XRD, SEM and Hall measurement.
• The ZT value of Sb0.23 at%-doped Mg2(Si0.95Ge0.05) was 0.74 at 756 K.

Magnesium silicide (Mg2Si) has recently attracted much interest as an n-type thermoelectric (TE) material for converting waste heat into electric power. The objective of this work was to reveal a mechanism to increase the thermoelectric properties of Mg2Si by Sb-doping and Ge-doping. Generally, Mg2Si is synthesized by all-molten method. However, this synthesis method has some problems, for example, mass defects of Mg for Mg2Si composition caused because the melting point of Mg2Si is very close to the boiling point of Mg. In this study, we tried to synthesize high purity Mg2Si from Mg and Si alloyed with a dopant (Sb, Ge) by spark plasma sintering (SPS). The Ge-doped samples had a higher ZT value than the ZT value of the Sb-doped sample of the same concentration without Ge because the thermal conductivity of the former was lower. The maximum ZT value of Sb0.23 at%-doped Mg2(Si0.995Ge0.05) was 0.74 at 756 K.