Intrinsically Minimal Thermal Conductivity in Cubic I-V-VI₂ Semiconductors

We report measurements of the thermal conductivity of high-quality crystals of the cubic I-V-VI₂ semiconductors AgSbTe₂ and AgBiSe₂. The thermal conductivity is temperature independent from 80 to 300 K at a value of approximately 0.70  W/mK. Heat conduction is dominated by the lattice term, which we show is limited by umklapp and normal phonon-phonon scattering processes to a value that corresponds to the minimum possible, where the phonon mean free path equals the interatomic distance. Minimum thermal conductivity in cubic I-V-VI₂ semiconductors is due to an extreme anharmonicity of the lattice vibrational spectrum that gives rise to a high Grüneisen parameter and strong phonon-phonon interactions. Members of this family of compounds are therefore most promising for thermoelectric applications, particularly as p-type materials.