Oxide-based thermoelectric materials have the advantages of high temperature stability, low toxicity and low processing cost comparted to other metal-based systems. However, achieving ZT>1 remain elusive especially for n-type bulk oxide thermoelectrics. Here, we report the experimental demonstration of ZT>1 in n-type oxides by synthesizing composites of Nb-doped SrTiO₃ (STN) with natural graphite. Introduction of conductive graphite inclusions in STN matrix has led to a surge in electrical conductivity due to 21-times increase in weighted mobility (${\mu }_w)$ of electrons resulting in high thermoelectric power factor ~5400 $\frac{\mathit{\mu W}}{m{K}^2}$, which is ~16-times higher than that of pure STN. Furthermore, we could restrain the increase in thermal conductivity by attaining enhanced Umklapp scattering along with phonon-glass-like temperature-independent phonon mean-free-path above Debye temperature. We have achieved the maximum ZT ~1.42 in STN+0.5 wt% G composite, which is 15-times enhancement compared to STN. Our proposed way of designing rare-earth-free composites with graphite can potentially open up the possibility of fabricating novel high-temperature thermoelectric generators.

与其他基于金属的系统相比，基于氧化物的热电材料具有高温稳定性，低毒性和低加工成本的优势。然而，尤其对于n型体氧化物热电而言，实现ZT＞ 1仍然是遥不可及的。在这里，我们通过合成Nb掺杂SrTiO ₃（STN）与天然石墨的复合材料，报告了n型氧化物中ZT> 1的实验演示。在STN基质中引入导电石墨夹杂物导致了电导率的激增，这是由于加权迁移率提高了21倍（${\mu }_w）$ 电子导致高的热电功率因数〜5400 $\frac{\mathit{微瓦}}{米{ķ}^2}$，比纯STN高约16倍。此外，我们可以通过获得增强的Umklapp散射以及高于Debye温度的类似于声子玻璃的温度独立声子平均自由程，来抑制热导率的增加。我们在STN + 0.5  wt％G复合材料中实现了最高ZT〜1.42 ，是STN的15倍。我们提出的用石墨设计无稀土复合材料的方法可能会潜在地制造新型高温热电发电机。