Intrinsically Minimal Thermal Conductivity in Cubic<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="normal">I</mml:mi><mml:mtext mathvariant="normal">−</mml:mtext><mml:mi mathvariant="normal">V</mml:mi><mml:mtext mathvariant="normal">−</mml:mtext><mml:msub><mml:mi>VI</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>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.