Mg(Sn,Si) and Mg(Sn,Ge) are promising n-type thermoelectric materials with good thermoelectric properties in the temperature range of 300e800 K. For power generation, similar thermoelectric performance of p-type materials is equally important. However, p-type material performance is much worse than the n-type, because achieving optimized carrier concentration has been difficult for the p-type Mg2X (X ¼ Sn, Si). In this study we systematically compared the effect of the dopants Li, Na, and Ga and found that the highest carrier concentrations are achievable in Li-doped samples. Due to the relatively high content of Sn, carrier concentration of > 5 � 1019 cm�3 were achieved for all dopants. Analysis of the transport data in the framework of a single parabolic band model showed similar and carrier concentration independent effective masses for all dopants. Our results therefore indicate a rigid band structure for p-type Mg2X for the studied dopants, in contrast to previous reports. Higher carrier mobilities have been achieved for Li-doped samples compared to the previous reports. Larger Hall mobilities leads to a higher peak power factor. Due to the higher carrier concentration, the onset of intrinsic excitations (bipolar effect) effectively shifts to higher temperature compared to the other two dopants, which results in a peak figure of merit of ~0.5 at 723 K for Li doped samples.

中文翻译：

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锂、钠、镓掺杂p型Mg 2 Sn 0.75 Ge 0.25的热电性能对比研究

Mg(Sn,Si) 和 Mg(Sn,Ge) 是很有前途的 n 型热电材料，在 300e800 K 的温度范围内具有良好的热电性能。对于发电，类似 p 型材料的热电性能同样重要。然而，p 型材料的性能比 n 型差得多，因为对于 p 型 Mg2X (X ¼ Sn, Si) 来说，实现优化的载流子浓度一直很困难。在这项研究中，我们系统地比较了掺杂剂 Li、Na 和 Ga 的影响，发现在 Li 掺杂的样品中可以获得最高的载流子浓度。由于 Sn 的含量相对较高，所有掺杂剂的载流子浓度都达到了 > 5 1019 cm 3。在单个抛物线带模型框架内对传输数据的分析表明，所有掺杂剂的有效质量相似且与载流子浓度无关。因此，与之前的报告相反，我们的结果表明所研究的掺杂剂的 p 型 Mg2X 具有刚性带结构。与之前的报告相比，锂掺杂的样品实现了更高的载流子迁移率。更大的霍尔迁移率导致更高的峰值功率因数。由于载流子浓度更高，与其他两种掺杂剂相比，本征激发（双极效应）的开始有效地转移到更高的温度，这导致 Li 掺杂样品在 723 K 时的峰值品质因数约为 0.5。与之前的报告相比，锂掺杂的样品实现了更高的载流子迁移率。更大的霍尔迁移率导致更高的峰值功率因数。由于更高的载流子浓度，与其他两种掺杂剂相比，本征激发（双极效应）的开始有效地转移到更高的温度，这导致 Li 掺杂样品在 723 K 时的峰值品质因数约为 0.5。与之前的报告相比，锂掺杂的样品实现了更高的载流子迁移率。更大的霍尔迁移率导致更高的峰值功率因数。由于更高的载流子浓度，与其他两种掺杂剂相比，本征激发（双极效应）的开始有效地转移到更高的温度，这导致 Li 掺杂样品在 723 K 时的峰值品质因数约为 0.5。