Intrinsically Ultra-low Lattice Thermal Conductivity and Excellent Thermoelectric Performance in Complex Layered Pb4In2.8Bi3.2Se13 Compound

The complex atomic structure of the Pb₄In_2.8Bi_3.2Se₁₃ compound has been investigated, crystallizing in orthorhombic Pbam (a = 22.093 Å, b = 27.398 Å, c = 4.1324 Å). Its crystal structure exhibits a 3D framework, wherein bicapped trigonal prisms of Pb²⁺ ions bridge InSe₄ tetrahedra and (Bi/In)Se₆ octahedra. This framework incorporates Z-shaped chains of distorted Bi³⁺ octahedra and linear chains of In³⁺ tetrahedra propagating along the c-axis. The synergistic effects of Pb/Bi s² lone-pair electron distortion-induced coordination environments and weak In–Se covalent bonds significantly suppress phonon propagation, resulting in intrinsically low v_a (1689 m s^–1) and ultra-low θ_D (86 K). These collectively enable intrinsically ultra-low κ_L (0.27 W m^–1 K^–1 at 723 K). Meanwhile, electronic transport properties were effectively optimized by doping with Cl, achieving a peak PF of 0.23 mW m^–1 K^–2 at 723 K. Consequently, the Cl-doped Pb₄In_2.8Bi_3.2Se_12.805Cl_0.195 compound reached ZT = 0.54 at 723 K, representing a 260% improvement over the undoped intrinsic sample.