(Invited) Reducing the Thermal Conductivity By Driving PbTe to a Phase Transition Via Strain and/or Alloying

The efficient control of thermoelectric energy conversion processes is highly desirable as nearly 60% of the consumed energy is wasted as heat. Low thermal conductivity is one of the key factors leading to high thermoelectric efficiency of a material [1]. However, one of the major obstacles in the design of materials with low lattice thermal conductivity is the difficulty in efficiently scattering phonons across the entire frequency spectrum [2]. Using first principles calculations, we show that driving PbTe materials to the brink of a Peierls-like phase transition could be a powerful strategy to solve this problem. We illustrate this concept by applying tensile [001] strain to PbTe and its alloy with a chemically similar material in the rock-salt structure (e.g. PbSe), and by alloying PbTe with a related material in the rhombohedral, Peierls-distorted, structure (e.g. GeTe). This induces extremely soft optical modes, which increases acoustic-optical phonon coupling and decreases phonon lifetimes at all frequencies. We predict that PbTe, Pb(Se,Te) and (Pb,Ge)Te alloys tuned in the described manner could have substantially reduced lattice thermal conductivity compared to PbTe. The proposed concept may open new opportunities for the development of more efficient thermoelectric materials. This work was done in collaboration with Ronan Murphy, Eamonn Murray and Stephen Fahy.

[1] G. J. Snyder and E. S. Toberer, Nature Mater. 7, 105 (2008).

[2] K. Biswas et al. Nature 489, 414 (2012).