Strong anharmonic phonon scattering induced giant reduction of thermal conductivity in PbTe nanotwin boundary

YG Zhou and JY Yang and L Cheng and M Hu, PHYSICAL REVIEW B, 97, 085304 (2018).

DOI: 10.1103/PhysRevB.97.085304

Lead telluride (PbTe) is a renowned thermoelectric material with high energy conversion efficiency in medium to high temperature range. However, the performance of PbTe at room temperature is poor due to its relatively high lattice thermal conductivity, which is difficult to be engineered due to its intrinsic very short phonon mean-free path. By performing systematic first-principles and molecular-dynamics simulations, we report that the room-temperature lattice thermal conductivity of PbTe can be reduced by almost one order of magnitude (86%) using the recent experimentally observed nanotwin structure. The mechanism responsible for the dramatic decrease of thermal conductivity strongly depends on the type and mass of atoms at the twin boundary. For PbTe nanotwinned structures with Te at the twin boundary, phonon transport is dominated by the phonon confinement effect and phonon-twin boundary scattering, and the thermal conductivity converges to the bulk value when half of the periodic length is larger than the dominant phonon mean-free path. The same phenomenon is found in another comparison system of KCl nanotwinned structures. However, when Pb is present at the twin boundary, a scattering mechanism occurs: anharmonicity induced by the twin boundary. Due to the mass difference between Pb and Te, the thermal resistance for Pb residing at the twin boundary is found to be one order of magnitude larger than the case with Te at the twin boundary, which results in much stronger phonon-twin boundary scattering. Consequently, the lowest thermal conductivity of such PbTe nanotwinned structure is only 0.4 W/mK, which is reduced by about sevenfold compared to the bulk value of 2.85W/mK; finally, the converged thermal conductivity cannot restore the bulk value even when half of the periodic length is much larger than the dominant mean-free path. These results offer useful guidance for the development of PbTe- based thermoelectrics and also suggest that nanotwins are excellent building blocks for enhancing the performance of existing thermoelectrics.

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