Synergistic Effect of Alloying on Thermoelectric Properties of Two-Dimensional Pdpq (Q = S, Se).
Physical Chemistry Chemical Physics : PCCP
Hosts of 2D materials exist, yet few allow compositional and structural tailoring as the MQ (M = Mo, W; Q = S, Se) family does, for which various structural superlattices have been synthesized. Using thorough first-principles calculations, we show how bonding hierarchy contributes to the structural resilience of 2D PdPQ and allows for full-range alloying of sulfur and selenium. Within the structural unit of PdPQ, the covalently-bonded [PQ] polyanions hold the structure together with their molecular-like P-P bonds while ionically bonded Pd-Qs allow the S/Se substitution. Here, the bonding hierarchy imparts superior electronic and structural features to the PdPQ monolayers. As such, the flat-and-dispersive valence band and the eight degenerate valleys of the conduction band benefit the p-type and n-type thermoelectricity of pristine PdPQ, which can be further enhanced by alloying. The high-entropy alloying synergistically suppresses the lattice heat transport from 75 to 30 W m K and increases the band degeneracy of PdPQ monolayers, resulting in an overall improvement in . Combining these features, in a naïve approach, results in a large approaching two for both p-type and n-type doping. However, accurate fully-fledged electron-phonon calculations rebut this promise, showing that at high temperatures, the increased electron scattering results in a stagnant power factor in the flat-and-dispersive valence band. Using a realistic first-principles scattering, we finally calculate the thermoelectric efficiency of PdPQ (Q = S, Se) and highlight the importance of an accurate estimation of electron relaxation time for thermoelectric predictions.
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Shahabfar, S., Xia, Y., Morshedsolouk, M. H., Bidhendi, M. M., & Naghavi, S. (2023). Synergistic Effect of Alloying on Thermoelectric Properties of Two-Dimensional PdP Q (Q= S, Se). Physical Chemistry Chemical Physics. https://doi.org/10.1039/D2CP05979G