Simultaneously achieving high ZT and mechanical hardness in highly alloyed GeTe with symmetric nanodomains

For the application of thermoelectric materials, high figure-of-merit, ZT, endows them high energy conversion efficiency, while robust mechanical hardness makes them tolerable to a large thermal stress and elongates their service life. Hence, both high ZT and high mechanical hardness are necessary for the application of thermoelectric materials. Here, we report the simultaneous achievement of high ZT and robust mechanical hardness in highly alloyed GeTe with symmetric nanodomains. By proper structural symmetry engineering via Mn-substitution at Ge site, highly symmetric cubic GeTe nanodomains have formed, which strengthens phonon scattering together with dense point defects, and correspondingly approaches the amorphous limit of lattice thermal conductivity. Simultaneously, the optimized carrier concentration and additional band convergence lead to high electrical performance. Correspondingly, an enhanced ZT of ∼ 2.3 in Ge_0.82Pb_0.1Bi_0.04Mn_0.04Te at 573 K with an average ZT of ∼ 1.6 (300 K to 723 K) is achieved, which refers to a maximum energy conversion efficiency of ∼ 17 % at temperature difference of 400 K. Moreover, the hierarchical structure features results in high Vickers hardness up to ∼ 207 Kgf mm⁻² in the Ge_0.82Pb_0.1Bi_0.04Mn_0.04Te. Our study indicates that structural symmetry engineering in highly alloyed GeTe can simultaneously approach significantly increased ZT and mechanical hardness, which can inspire new exploration and application of GeTe-based materials.