Fig. 1: Nanotwin architecture and ultra-high valley degeneracy leads to high thermoelectric performance and mechanical properties.

a Modulation mechanism of nanotwins, ordered vacancy arrays, and point defects on phonon transport. b CuBiS2 alloying leads to band alignment and ultra-high valley degeneracy (Nv) of 22. c Comparison of thermoelectric performance and mechanical properties between pristine GeTe and (GeTe)0.93(CuBiS2)0.07 sample.