# Enhancement of thermoelectric performance across the topological phase transition in dense lead selenide

## Abstract

Alternative technologies are required in order to meet a worldwide demand for clean non-polluting energy sources. Thermoelectric generators, which generate electricity from heat in a compact and reliable manner, are potential devices for waste heat recovery. However, thermoelectric performance, as encapsulated by the figure of merit ZT, has remained at around 1.0 at room temperature, which has limited practical applications. Here, we study the effects of pressure on ZT in Cr-doped PbSe, which has a maximum ZT of less than 1.0 at a temperature of about 700 K. By applying external pressure using a diamond anvil cell, we obtained a room-temperature ZT value of about 1.7. From thermoelectric, magnetoresistance and Raman measurements, as well as density functional theory calculations, a pressure-driven topological phase transition is found to enable this enhancement. Experiments also support the appearance of a topological crystalline insulator after the transition. These findings point to the possibility of using compression to increase not just ZT in existing thermoelectric materials, but also the possibility of realizing topological crystalline insulators.

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## Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

## Code availability

All the codes created for the analysis of the data are from the open-source software packages which are cited in the references of this paper.

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## Acknowledgements

The work at HPSTAR was supported by the National Key R&D Programme of China (grant no. 2018YFA0305900). The work performed at the University of Houston was funded by the Department of Energy’s Basic Energy Science programme under grant no. DE-SC0010831. The work at Carnegie was funded by the US National Science Foundation under grant no. EAR-1763287. P.Q.C. acknowledges the internship programme at Carnegie Institution of Washington.

## Author information

X.J.C. conceived the project. X.J.C. and Z.R. designed the project. Q.Z. and Z.R. synthesized the samples. L.C.C. and V.V.S. performed high-pressure X-ray diffraction measurements. P.Q.C. and A.F.G. performed high-pressure Raman spectroscopy measurements. L.C.C. and X.J.C. performed the TE properties measurements. W.J.L. and X.J.C. carried out the density functional theory calculations. All of the authors analysed the data and discussed the underlying physics. X.J.C. wrote the paper with contributions from the other authors. The manuscript reflects the contributions of all authors.

Correspondence to Xiao-Jia Chen.

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## Supplementary information

### Supplementary Information

Supplementary Table 1, Figs. 1–11, Notes 1–6 and references.

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