Australian Institute for Innovative Materials (AIIM), Innovation Campus, University of Wollongong, Wollongong, NSW 2500, Australia.
Electron Microscopy Centre (EMC), Innovation Campus, University of Wollongong, Wollongong, NSW 2500, Australia.
Sci Rep. 2017 Jun 21;7(1):3988. doi: 10.1038/s41598-017-04348-7.
Magnesium-based thermoelectric materials (MgX, X = Si, Ge, Sn) have received considerable attention due to their availability, low toxicity, and reasonably good thermoelectric performance. The synthesis of these materials with high purity is challenging, however, due to the reactive nature and high vapour pressure of magnesium. In the current study, high purity single phase n-type MgGe has been fabricated through a one-step reaction of MgH and elemental Ge, using spark plasma sintering (SPS) to reduce the formation of magnesium oxides due to the liberation of hydrogen. We have found that Bi has a very limited solubility in MgGe and results in the precipitation of MgBi. Bismuth doping increases the electrical conductivity of MgGe up to its solubility limit, beyond which the variation is minimal. The main improvement in the thermoelectric performance is originated from the significant phonon scattering achieved by the MgBi precipitates located mainly at grain boundaries. This reduces the lattice thermal conductivity by ~50% and increases the maximum zT for n-type MgGe to 0.32, compared to previously reported maximum value of 0.2 for Sb-doped MgGe.
镁基热电材料（MgX，X = Si、Ge、Sn）由于其可用性、低毒性和相当好的热电性能而受到广泛关注。然而，由于镁的反应性和高蒸气压，这些材料的高纯度合成具有挑战性。在当前的研究中，通过 MgH 和元素 Ge 的一步反应，使用火花等离子烧结（SPS）来减少由于氢气释放而形成的氧化镁，制备出了高纯度单相 n 型 MgGe。我们发现 Bi 在 MgGe 中的溶解度非常有限，导致 MgBi 的沉淀。Bi 掺杂将 MgGe 的电导率提高到其溶解度极限，超过此极限，变化很小。热电性能的主要改善源于主要位于晶界处的 MgBi 沉淀物对声子散射的显著影响。这将晶格热导率降低了约 50%，并将 n 型 MgGe 的最大 zT 值提高到 0.32，相比之下，之前报道的 Sb 掺杂 MgGe 的最大 zT 值为 0.2。
