Remarkable Thermoelectric Performance in K₂CdPb Crystals with 1D Building Blocks via Structure Particularity and Bond Heterogeneity

Identifying approaches that reduce thermal conductivity with little impact on electrical transport performance remains a central challenge for the thermoelectric community. Here, we use density functional theory calculations to demonstrate that K₂CdX (XSn, Pb), with a crystal structure composed of a one-dimensional zigzag Cd-X chain sublattice and an isolated alkali metal K atom, exhibits favorable electronic and phonon transport as well as superior thermoelectric conversion efficiency. We reveal that the presence of a long-range ionic bond and multiple band characteristics lead to “electron crystal”-like electrical transport performance. On the other hand, the ultralow lattice thermal conductivity (κ_L) of the K₂CdX compound mainly originates from the strong structural anharmonicity, which is caused by a low-dimensional sublattice combined with the heterogeneity of a weak chemical bond and the rattling vibration of K atoms in a crystal matrix. As a result, high average carrier mobility (>20 cm² V^–1 S^–1), low lattice thermal conductivity below 0.4 W/mK, and spectacularly high average zT larger than 2.0 predicted for the K₂CdPb system highlight the direction for identifying compounds with potential thermoelectric performance in this crystal family.