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A2: Medium temperature materials

Enhanced thermoelectric figure-of-merit in spark plasma sintered nanostructured p-type Mg3Sb2-based Zintl phase compounds

A. Bhardwaj, D. K. Misra* and A. Dhar
CSIR-Network of Institutes for Solar Energy, Materials Physics & Engineering Division, CSIR-National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi-110012, India.

Mg3Sb2-based Zintl phase compounds are known to be cost effective and environmental friendly due to which they are potential materials for thermoelectric devices in the intermediate temperature range. Recently, we had reported a thermoelectric figure of merit (ZT) ~ 0.60 at 750 K in single phase p-type Mg3Sb1.8Bi0.2 Zintl compound, synthesized directly using spark plasma sintering. In this study, nanostructuring of p-type Mg3Sb2 and Mg3Sb1.8Bi0.2 have been performed employing high energy ball milling followed by their rapid heating using spark plasma sintering technique. The rapid-heating rates, used in spark plasma sintering leads to high density, while maintaining the nanostructural features introduced during ball-milling. More than 50% enhancement in ZT over their bulk counterparts values was observed for both, nanostructured Mg3Sb2 (ZT~ 0.4) and Mg3Sb1.8Bi02 (ZT~ 0.94) alloys. The improved ZT in these nanostructured alloys is due to drastic reduction in thermal conductivity coupled with a simultaneous enhancement in the Seebeck coefficient. The measured thermal and electrical transport in these synthesized thermoelectric nanostructured alloys is discussed in the light of observed microstructures investigated by high resolution transmission electron microscopy.

*Corresponding author: E-mail address: misradk@nplindia.org OR dakkmisra@gmail.com (DKM)