Structural and physical properties of Mg3−xZnxSb2 (x=0–1.34)

The Mg3−xZnxSb2 phases with x=0–1.34 were prepared by direct reactions of the elements in tantalum tubes. According to the X-ray single crystal and powder diffraction, the Mg3−xZnxSb2 phases crystallize in the same P3¯m1 space group as the parent Mg3Sb2 phase. The Mg3−xZnxSb2 structure is different from the other substituted structures of Mg3Sb2, such as (Ca, Sr, Ba) Mg2Sb2 or Mg5.23Sm0.77Sb4, in a way that in Mg3−xZnxSb2 the Mg atoms on the tetrahedral sites are replaced, while in the other structures Mg on the octahedral sites is replaced. Thermoelectric performance for the two members of the series, Mg3Sb2 and Mg2.36Zn0.64Sb2, was evaluated from low to room temperatures through resistivity, Seebeck coefficient and thermal conductivity measurements. In contrast to Mg3Sb2 which is a semiconductor, Mg2.36Zn0.64Sb2 is metallic and exhibits an 18-times larger dimensionless figure-of-merit, ZT, at room temperature. However, thermoelectric performance of Mg2.36Zn0.64Sb2 is still poor and it is mostly due to its large electrical resistivity.

The Mg atoms in Mg3Sb2 were successfully substituted with Zn, with Zn going exclusively into the tetrahedral sites. Zn substitution increases the electrical conductivity in Mg2.36Zn0.64Sb2 by closing the band gap. This change combined with a decrease in the thermal conductivity improves the ZT value.Figure optionsDownload as PowerPoint slide