The complex coupling between thermoelectric parameters makes it extremely challenging to improve the performance of materials. Typically, the reduction of thermal conductivity by incorporating porous structures often leads to a compromise in electrical conductivity. Herein, we present high-ion-conductive zeolite X (including Na-, Ca-, and Li-low silica type-X (LSX)) as the subnanoporous additive in the Bi_0.4Sb_1.6Te₃ (BST) matrix. Owing to the high pore charge density of zeolite X, the decrease in conductivity is effectively suppressed while maintaining a low thermal conductivity. Positively charged metal cation (M⁺) and valence electron of oxygen atom in aluminum-oxide tetrahedron of zeolite X achieve charge balance. Cationic with different electronegativity regulated electrons of oxygen atom transferred from the oxygen atoms to the BST matrix. The lower electronegativity of Na⁺ leads to a higher electron density surrounding oxygen atoms in Na-LSX. Thus, more electrons are transferred to the BST matrix from the oxygen atoms in Na-LSX and form Te–O bonds. Ultimately, the figure-of-merit (ZT) peak of BST/0.8 wt.% Na-LSX nanocomposites reached 1.47 at 373 K, with a huge cooling temperature difference of 69.4 K and an excellent thermoelectric conversion efficiency of 6.95%. This work exploits the stable and unique three-dimensional pore structure of X-type molecular sieves, broadening their potential application in the thermoelectric medium temperature range.

Metastable materials offer a broad and novel platform for the development of next-generation science and technology. Phase engineering including synthesis of materials with unconventional phases and phase transition of metastable materials has been explored in layered materials but has not tackled their anisotropy issue yet. The high anisotropy in layered materials further adds the cost of orientation screening of materials. Herein, we report the effect of Ag doping on facilitating the formation of metastable π-cubic phase SnS during the solvothermal synthesis process. On this basis, we construct cubic-to-orthorhombic (CTO) samples and elucidate the intrinsic mechanisms of its nearly isotropic thermoelectric properties by characterizing the texturing information and analyzing the valence charge density calculated by density functional theory (DFT). This work demonstrates a convenient approach to synthesize layered materials with isotropic electrical and thermal transport behaviors through a precursor of metastable phase.

PbS-based thermoelectric materials have attracted extensive attention in recent years for the advantages of earth abundancy and low cost, which is considered to be a substitute for traditional PbTe material. However, their high thermal conductivity restricts its development. Hence, in order to improve their thermoelectric performance from reducing the thermal conductivity, a kind of dendritic PbS with controlled crystal grain and morphology are obtained by solution synthesis. By adjusting the amount of surfactant (CTAB), the specific formation process of dendrites is regulated. After sintering, the dendritic PbS nanoparticles are easy to form porous structure due to the overlapping and staggered arrangement of dendritic branches. For comparison, we also prepare a kind of regular octahedral PbS and a dense packing arrangement is formed because of the integrity of the octahedral structure. DFT-based Boltzmann transport equation is used to prove the crucial role of porous structure in scattering phonon. Finally, a maximum zT = 1.0 at 773 K in n-type PbS is obtained, which still keep a high-speed growth and is expected to get higher zT value in a higher temperature region. Our work may shed light to other thermoelectric materials from the formation of porous structure to reduce the thermal conductivity.