High-symmetry thermoelectric materials usually have the advantage of very high band degeneracy, while low-symmetry thermoelectrics have the advantage of very low lattice thermal conductivity. If the symmetry breaking of band degeneracy is small, both effects may be realized simultaneously. Here we demonstrate this principle in rhombohedral GeTe alloys, having a slightly reduced symmetry from its cubic structure, to realize a record figure of merit (zT ∼ 2.4) at 600 K. This is enabled by the control of rhombohedral distortion in crystal structure for engineering the split low-symmetry bands to be converged and the resultant compositional complexity for simultaneously reducing the lattice thermal conductivity. Device ZT as high as 1.3 in the rhombohedral phase and 1.5 over the entire working temperature range of GeTe alloys make this material the most efficient thermoelectric to date. This work paves the way for exploring low-symmetry materials as efficient thermoelectrics.

高对称热电材料通常具有非常高的带简并性的优势，而低对称热电材料具有非常低的晶格热导率的优势。如果频带简并性的对称破坏较小，则可以同时实现两种效果。在这里，我们在菱面体GeTe合金中展示了这一原理，该合金的立方结构的对称性略有降低，从而在600 K时实现了创纪录的品质因数（zT〜2.4）。这可以通过控制工程中晶体结构中的菱面体畸变来实现分裂的低对称带将被收敛，以及同时降低晶格热导率的合成复杂性。设备ZT在菱面体相中高达1.3，在GeTe合金的整个工作温度范围内高达1.5，使该材料成为迄今为止最有效的热电材料。这项工作为探索低对称材料作为有效的热电学铺平了道路。