NRCN, P.O. Box 9001, Beer-Sheva 84190, Israel.
Phys Chem Chem Phys. 2019 Apr 3;21(14):7524-7533. doi: 10.1039/c9cp00764d.
Half-Heusler, HH, alloys are widely used n-type materials in thermoelectric applications. Today, there is a shortage in p-type HH based materials, which may have an inherent compatibility with the HH n-type pair. Al is a good candidate as an acceptor doping element for this purpose, and the results on alloying of TiNiSn-based HH with Al are reported in details. Combination of CALPHAD and ab initio DFT calculations with an experimental validation was carried out. It is demonstrated that low level Al doping leads to p-type conductivity of the material. The solubility of Al was predicted by calculations and experimentally confirmed. The stable phases with compositions above the solubility limit of Al were determined, including an assessment of the maximal Al solubility in the HH (Ti1-cAlc)NiSn phase up to 1400 K. In addition, a Scheil solidification simulation with the known TiNiSn CALPHAD database was used, in order to further understand the as-cast phase structure. It is shown that beyond the solubility limit the stable phases at room temperature are TiNiSn(HH), Sn(BCT) and NiAl(B2). The maximal solubility of Al in the HH phase is estimated as ∼1 at% at 1400 K. These results give the basic route for designing of (Ti1-cAlc)NiSn as a p-type thermoelectric element.
半 Heusler（HH）合金是热电应用中广泛使用的 n 型材料。如今，p 型 HH 基材料短缺，这可能与其 HH n 型对具有内在兼容性。Al 是作为施主掺杂元素的一个很好的候选者，本文详细报道了 TiNiSn 基 HH 与 Al 的合金化结果。通过实验验证，结合 CALPHAD 和从头算 DFT 计算进行了组合。结果表明，低水平的 Al 掺杂会导致材料呈现 p 型导电性。通过计算预测了 Al 的溶解度，并通过实验进行了验证。确定了超过 Al 溶解度极限的稳定相，包括评估 HH（Ti1-cAlc）NiSn 相中的最大 Al 溶解度可达 1400 K。此外，还使用了已知的 TiNiSn CALPHAD 数据库进行 Scheil 凝固模拟，以便进一步了解铸态相结构。结果表明，超过溶解度极限，室温下的稳定相为 TiNiSn（HH）、Sn（BCT）和 NiAl（B2）。在 1400 K 时，HH 相中 Al 的最大溶解度估计约为 1%。这些结果为设计（Ti1-cAlc）NiSn 作为 p 型热电元件提供了基本途径。
