Interstitial Defects Improving Thermoelectric SnTe in Addition to Band Convergence

Abstract

SnTe, as a top Pb-free alternative to PbTe, attracts extensive attention for thermoelectric applications. For thermoelectric performance enhancement, successful electronic strategies are typified by band convergence and resonant doping, while effective thermal strategies include nanostructuring and, recently, interstitial defects. This work demonstrates that phonon scattering by interstitial defects, as a nearly immune strategy integratable to band convergence, independently reduces the lattice thermal conductivity to the amorphous limit. This leads to a zT as high as 1.4 in Sn1–y Mg y Te­(Cu2Te) x , where Cu2Te acts as the source of interstitial defects while MgTe converges the valence bands. Evolutionarily, either Cu2Te or MgTe enables a ∼100% zT-enhancement as compared with that of pristine SnTe, while an overall ∼200% enhancement is successfully realized when both exist. This work not only improves SnTe as an eco-friendly alterative to thermoelecric PbTe but also demonstrates an approach potentially applicable for improving thermoelectrics.

Promising and Eco‐Friendly Cu2X‐Based Thermoelectric Materials: Progress and Applications

“…Both Zhao et al and Liu et al have reported the peak zT value of SnSe can be higher than 2 when the temperature is above 800 K. Meanwhile, most other results suggest the peak zT values of SnSe are at the temperature range lower than 800 K . When the temperature is between ≈800 and ≈1000 K, Cu 2 X, PbX (X = Te, Se, and S), SnTe as well as low‐cost and stable BiCuSeO are more attractive. Through nonequilibrium processing, Tan et al have achieved a record‐high zT value of 2.5 in Pb 0.98 Na 0.02 Te‐8%SrTe at 923 K. As a potential substitution for highly toxic PbTe, peak zT values of SnTe of ≈1.5 have also been widely reported .…”

“…When the temperature is between ≈800 and ≈1000 K, Cu 2 X, PbX (X = Te, Se, and S), SnTe as well as low‐cost and stable BiCuSeO are more attractive. Through nonequilibrium processing, Tan et al have achieved a record‐high zT value of 2.5 in Pb 0.98 Na 0.02 Te‐8%SrTe at 923 K. As a potential substitution for highly toxic PbTe, peak zT values of SnTe of ≈1.5 have also been widely reported . More interestingly, multiple studies demonstrate that the peak zT values of superionic Cu 2 X‐based thermoelectric materials can be higher than 2 in the temperature range from ≈800 to ≈1000 K (mainly Cu 2 Se‐based ones) .…”

Solute manipulation enabled band and defect engineering for thermoelectric enhancements of SnTe

“…Greatly inspired by the successful strategies for zT enhancements realized in PbTe with alloying, monotelluride solutes such as MnTe, MgTe, CdTe, CaTe, and HgTe are found to successfully minimize the ∆ E L‐∑ for an electronic improvement of SnTe. Among these solutes, MnTe is found to be one of the most effective for maximizing the valence band degeneracy ( N v ) due to its high solubility of ~15 at% .…”

“…Unfortunately, compared with PbTe, SnTe shows a much larger ΔE L-Σ of 12 to 15 k B T at room temperature, 51 and the lighter atomic mass leads to a much higher lattice thermal conductivity. 37,52 Eventually, pristine SnTe even with an optimal carrier concentration shows a peak zT of only 0.6 at 700 K. 53 Greatly inspired by the successful strategies for zT enhancements realized in PbTe with alloying, monotelluride solutes such as MnTe, 37,54,55 MgTe, [56][57][58] CdTe, [59][60][61] CaTe, 62 and HgTe 63 are found to successfully minimize the ΔE L-Σ for an electronic improvement of SnTe. Among these solutes, MnTe is found to be one of the most effective for maximizing the valence band degeneracy (N v ) due to its high solubility of~15 at%.…”

“…64 It should be noted that a high zT realized in above mentioned alloys usually involves a further Cu 2 Te alloying 54,64,65 for a sufficiently reduced κ L through the strong phonon scattering by Cu interstitials 52 and an excess of Sn for reducing the carrier concentration. Precipitation of excessive Sn and Cu 2 Te particularly at low temperatures 54,56,64,65 might lead to diffusion problems for practical applications. This motivates the search of single-phase solid solutions with a comparable or even higher zT.…”