Enhanced Thermoelectric Properties in One-Dimensional Mg/Ge Nanostructures

Abstract

High figure-of-merit (ZT) thermoelectric (TE) materials that efficiently convert heat into electricity have attracted great attention for providing a promising solution to sustainable energy technology. For a high performance TE material, the concurrent of low thermal conductivity (κ) and high electrical conductivity (σ) is essential since ZT increases linearly with σ and is inversely proportional to κ. Nanostructuring TE materials that effectively reduces lattice conductivity in conjunction with no apparent influence on electrical properties, has been recognized as the most effective approach for increasing the ZT. Therefore, it has been demonstrated that one-dimensional nanostructures could reduce the κ by hindering the carrier transport and phonon scattering, thereby leading to the enhancement of ZT. Mg2X-based (where X can be Si, Ge, Sn, or Pb) compounds are cost-effective and eco-friendly candidates for commercial applications in mid-temperature thermoelectric power generation. More importantly, these material systems have the advantage of integrating with existing Si-based integrated circuits. Recently, bulk state of Mg2Ge with ZT=0.3 at 700K has been reported. In this study, we utilize electrospinning method combining with thin-film deposition technique to fabricate one-dimensional Mg/Ge nanostructures with different composition ratios. We also fabricate suspended micro-fabricated devices for measuring thermal and electrical transport in these one-dimensional Mg/Ge nanostructures. It was found that the (Mg2Ge+Ge) sample has the highest ZT value of 0.45 at 600K among all one-dimensional Mg/Ge nanostructures. This ZT enhancement can be attributed to the lower κ, which results from the enhanced phonon scattering in one-dimensional nanostructures.