Low thermal conductivity and good thermoelectric performance in mercury chalcogenides

Thermoelectric (TE) property refers to converting thermal energy into electrical energy via Seebeck effect. Theoretically, the presence of a low thermal conductivity and a high thermoelectric power factor in a same material promises a good thermoelectric performance. In this paper, we investigate the thermal transport and thermoelectric properties of crystalline mercury chalcogenides (HgX, X = O, S, Se, Te) based on first-principles calculations combined with Boltzmann transport equation and electron-phonon interaction (EPI). Remarkably, the calculated lattice thermal conductivity kappa(L) of the semiconducting mercury chalcogenides (alpha-HgO and alpha-HgS) are fairly low (kappa(L)similar to 0.60 W/mK at 300 K, which is about 38% of the value for the typical thermoelectric material PbTe), while the corresponding power factors S-2 sigma for alpha-HgS are relatively high, which, as a result, leads to a good thermoelectric performance in alpha-HgS, with the thermoelectric figure of merit ZT even exceeding 1.28. However, the highest ZT of alpha-HgO is only 0.58 due to the relatively low S-2 sigma. For comparison, the lattice thermal conductivity kappa(L) of the semimetallic mercury chalcogenides (beta-HgS, beta-HgSe, and beta-HgTe) are much higher than that of PbTe, limiting the applications in thermoelectricity. These results indicate that semiconducting mercury chalcogenides may be potential candidates for the design of thermoelectric generators.