Less-expensive and abundantly available Hf-free half-Heusler (HH) alloys are promising candidates for mid-temperature thermoelectric (TE). In the present work, we combine experimental outcomes with theoretical estimates to understand, design, and synthesize, Hf-free ZrNiSn_1–xGe_x based HH alloys with enhanced TE performance. A state-of-the-art TE figure-of-merit (ZT) ∼ 0.92 at around 873 K was achieved for the optimal ZrNiSn_0.97Ge_0.03 HH composition, wherein Ge atoms substitute Sn interstitial sites, as confirmed and understood by X-ray analysis and first-principles calculations, respectively. The isoelectronic Ge-doping improves electronic transport due to enhancement in carrier mobility. Concurrently, the reduction in thermal conductivity is attained by enhanced phonon scattering owing to mass fluctuation and strain field effects. The present work exhibits the efficacy of Ge as an effective dopant for HH alloys and strengthens the possibility of developing Hf-free cost-effective HH materials with high TE performance.

中文翻译：

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等电子锗掺杂对ZrNiSn热电性能的能带结构修饰和质量涨落效应

廉价且大量可用的无Hf半霍斯勒（HH）合金是中温热电（TE）的有前途的候选者。在目前的工作中，我们将实验结果与理论估算值结合起来，以理解，设计和合成具有增强的TE性能的无Hf ZrNiSn ₁ - _x Ge _x基HH合金。对于最佳ZrNiSn _0.97 Ge _0.03，在约873 K时获得了最先进的TE品质因数（ZT）〜0.92分别由X射线分析和第一性原理计算确认和理解的HH成分，其中Ge原子取代了Sn间隙位点。由于载流子迁移率的提高，等电子锗掺杂改善了电子传输。同时，由于质量波动和应变场效应，通过增强声子散射可以降低导热系数。本工作展示了Ge作为HH合金的有效掺杂剂的功效，并增强了开发具有高TE性能的无Hf低成本HH材料的可能性。