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Journal of materials chemistry / A 10(3), 1473 - 1480 (2022). doi:10.1039/D1TA09489K, In recent years hierarchical thermoelectric materials have been engineered to reach record breaking thermoelectric figures-of-merit (zT) making them attractive in green transition energy conversion applications. PbTe constitutes an archetypical example, where PbS nanoinclusions presumably scatter phonons, while leaving the electrical properties intact. For widespread use of such materials, their structural integrity and chemical stability are equally important to the thermoelectric performance. Here, we show by operando X-ray diffraction and physical property measurements that PbS nanoinclusions in PbTe are not stable at operating conditions. The PbS nanoinclusions grow in size, but surprisingly this does not diminish the thermoelectric performance. Comparison with samples without nanostructures reveals that the PbS inclusions primarily affect the electrical properties at elevated temperatures, and to a lesser degree the lattice thermal conductivity. Nanostructured materials have significantly moved thermoelectric performance limits, but if we are to develop materials by design rather than trial-and-error, it is important that the nature, effect and stability of nanoinclusions are characterized under operating conditions., Published by RSC, London [u.a.]

The discovery of novel materials for thermoelectric energy conversion has potential to be accelerated by data-driven screening combined with high-throughput calculations. One way to increase the efficacy of successfully choosing a candidate material is through its evaluation using transport descriptors. Using a data-driven screening, we selected 12 potential candidates in the trigonal ABX2 family, followed by charge transport property simulations from first principles. The results suggest that carrier scattering processes in these materials are dominated by ionised impurities and polar optical phonons, contrary to the oft-assumed acoustic-phonon-dominated scattering. Using these data, we further derive ground-state transport descriptors for the carrier mobility and the thermoelectric powerfactor. In addition to low carrier mass, high dielectric constant was found to be an important factor towards high carrier mobility. A quadratic correlation between dielectric constant and transport performance was established and further validated with literature. Looking ahead, dielectric constant can potentially be exploited as an independent criterion towards improved thermoelectric performance. Combined with calculations of thermal conductivity including Peierls and inter-branch coherent contributions, we conclude that the trigonal ABX2 family has potential as high performance thermoelectrics in the intermediate temperature range for low grade waste heat harvesting. Agency for Science, Technology and Research (A*STAR) National Research Foundation (NRF) T. D., M. B. S., G. W., and S.-W. Y. acknowledge the support of Agency for Science, Technology and Research (A*STAR) of Singapore (Grant No. 1527200024). J. R.-G., D. V. M. R., P. K., A. A., and K. H. would like to acknowledge the Accelerated Materials Development for Manufacturing Program at A*STAR via the AME Programmatic Fund by the Agency for Science, Technology and Research under Grant No. A1898b0043. K. H. would like to acknowledge funding via the NRF Fellowship NRF-NRFF13-2021. J. R.-G. and I. N. would like to thank A*STAR Graduate Academy's ARAP programme for funding J. R.-G.'s graduate studies in IMRE, A*STAR. M. O. and J. S. would like to acknowledge JSPS KAKENHI (19H00744, 20K14661) and JST CREST (JPMJCR20Q3).

The interactions between electrons and lattice vibrations are fundamental to materials behaviour. In the case of group IV–VI, V and related materials, these interactions are strong, and the materials exist near electronic and structural phase transitions. The prototypical example is PbTe whose incipient ferroelectric behaviour has been recently associated with large phonon anharmonicity and thermoelectricity. Here we show that it is primarily electron-phonon coupling involving electron states near the band edges that leads to the ferroelectric instability in PbTe. Using a combination of nonequilibrium lattice dynamics measurements and first principles calculations, we find that photoexcitation reduces the Peierls-like electronic instability and reinforces the paraelectric state. This weakens the long-range forces along the cubic direction tied to resonant bonding and low lattice thermal conductivity. Our results demonstrate how free-electron-laser-based ultrafast X-ray scattering can be utilized to shed light on the microscopic mechanisms that determine materials properties., Group IV–VI materials often exist in a state near an electronic or structural phase transition. Here, the authors use ultrafast X-ray scattering to show that coupling of band-edge electrons and phonons causes the ferroelectric instability observed in lead telluride.

We investigate vibrational behaviors in misch-metal filled antimony skutterudites in the time domain. At higher filling ratios of guest atoms, the vibration frequency approaches that of the cage structure and the amplitude becomes stronger. Furthermore, the reduction of lattice thermal conductivity over a wide temperature range can be explained using the measured resonant vibrational frequency. These findings reveal that the reduction of the lattice thermal conductivity is a result of scattering of acoustic phonons due to the resonant interaction between guest atoms and lattice phonons.