Intrinsically Ultra-low Lattice Thermal Conductivity and Excellent Thermoelectric Performance in Complex Layered Pb₄In_2.8Bi_3.2Se₁₃ Compound

The complex atomic structure of the Pb4In2.8Bi3.2Se13 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 va (1689 m s–1) and ultra-low θD (86 K). These collectively enable intrinsically ultra-low κL (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 Pb4In2.8Bi3.2Se12.805Cl0.195 compound reached ZT = 0.54 at 723 K, representing a 260% improvement over the undoped intrinsic sample.