Anomalous Thermal Conductivity and High Thermoelectric Performance of Cubic Antiperovskites K₃IX(Se & Te)

The performance of thermoelectric (TE) materials is restricted by the coupling between electronic and phonon transport. On the basis of first-principles calculations, self-consistent phonon theory, and the Boltzmann transport equation, this study proposes a novel class of cubic weak-bonding antiperovskites, K 3 IX(Se & Te), which has not been synthesized thus far. These materials exhibit strong lattice anharmonicity and enable the separation of electronic and phonon transport at the atomic level. With quartic anharmonicity correction, antiperovskites K 3 I(Se & Te) are predicted to exhibit remarkably low lattice thermal conductivities κ L . At room temperature, the calculated κ L values of K 3 ISe and K 3 ITe are only 0.60 and 0.18 W m –1 K –1, respectively. Additionally, these types of materials demonstrate an anomalously weak temperature dependence of κ L, approximately conforming to a power-law relationship where κ L ∼ T –0.3 for K 3 ITe. Simultaneously, the high degeneracy and nearly flat band structure endow K 3 IX(Se & Te) with large power factors when doped. At 800 K, under p-type doping, the calculated ZT values of K 3 ISe and K 3 ITe can reach 1.33 and 2.61, respectively, surpassing those of the leading traditional TE materials. The results have revealed that K 3 IX(Se & Te) represent a promising class of TE materials exhibiting excellent performance, and the structural features that effectively decouple phonon and electron transport also offer novel perspectives for the investigation of high-performance TE materials.