Nanostructured Ferecrystal\nIntergrowths with TaSe<sub>2</sub> Unveiled High Thermoelectric Performance\nin <i>n</i>‑Type SnSe

Ferecrystals, a distinctive class of misfit layered compounds,\nhold significant promise in manipulating the phonon transport owing\nto their two-dimensional (2D) natural superlattice-type structure\nand turbostratic (rotational) disorder present between the constituent\nlayers. Integrating these 2D intergrowth structures as nanodomains\nembedded in a bulk thermoelectric matrix is a formidable challenge\nin synthetic chemistry, yet offers groundbreaking opportunities for\nefficient thermoelectrics. Here, we have achieved an exceptionally\nhigh thermoelectric figure of merit, <i>zT</i> ∼\n2.2, at 823 K in <i>n</i>-type Ta and Br-codoped SnSe, by\nsuccessfully incorporating [(SnSe)<sub>1.15</sub>]<sub>7</sub>(TaSe<sub>2</sub>)<sub>1</sub> ferecrystals with [110] SnSe//[100] TaSe<sub>2</sub> orientation, as nanostructures with modulations in few nm\nin bulk SnSe solid-state matrix. While the presence of ferecrystal\nnanostructures induces strong scattering of heat-carrying phonons\nresulting in an ultralow lattice thermal conductivity (κ<sub>L</sub>) of ∼0.18 W m<sup>–1</sup> K<sup>–1</sup> at 773 K, the Ta and Br codoping strategy increases the concentration\nof <i>n</i>-type charge carriers for enhanced electrical\nconductivity. Our approach provides a new pathway for damping the\nphonon transport and enhancing the thermoelectric performance in 2D\nlayered materials.