Glassy ZIF-62 compositing induces ultralow lattice thermal conductivity in GeTe

A glassy zeolitic imidazolate framework-62 (g-ZIF-62) is used to composite with GeTe for effectively enhancing the mid-frequency phonon scattering to decrease the thermal conductivity of GeTe. After compositing, g-ZIF-62 distributes at the grain boundary of GeTe, leading to reduced lattice thermal conductivity (κ_l) of 0.31 W m^–1 K^–1 at 673 K, which is close to the theoretical amorphous limit of GeTe. Meanwhile, the introduction of g-ZIF-62 refrains the hall mobility and electrical conductivity, thus leading to minimized electrical thermal conductivity (κ_e). Accordingly, such g-ZIF-62 compositing can solely increase the ZT (dimensionless figure of merit) of GeTe of around 32 % at 723 K, even though the other parameters are not technically optimized for improving thermoelectric properties of GeTe. This study suggests that compositing g-ZIF-62 with GeTe can effectively strengthen the mid-frequency phonon scattering to decrease κ_l and κ_e of GeTe, providing a reasonable way to enhance the ZT of the thermoelectric materials.