# Broadband Phonon Scattering in PbTe-based Materials Driven Near the Ferroelectric Phase Transition by Strain or Alloying

## TL;DR

This paper proposes that approaching the ferroelectric phase transition in PbTe-based materials via strain or alloying significantly enhances phonon scattering, thereby reducing thermal conductivity and improving thermoelectric efficiency.

## Contribution

It introduces a novel strategy of using strain and alloying to induce soft optical modes in PbTe materials, enhancing phonon scattering across all frequencies.

## Key findings

- PbTe and related alloys exhibit 2-3 times lower thermal conductivity near the phase transition.
- Applying tensile strain or alloying induces soft optical modes that increase anharmonic phonon interactions.
- The approach offers a new pathway for designing high-performance thermoelectric materials.

## Abstract

The major obstacle in the design of materials with low lattice thermal conductivity is the difficulty in efficiently scattering phonons across the entire frequency spectrum. Using first principles calculations, we show that driving PbTe materials to the brink of the ferroelectric phase transition could be a powerful strategy to solve this problem. We illustrate this concept by applying tensile [001] strain to PbTe and its alloys with another rock-salt IV-VI material, PbSe; and by alloying PbTe with a rhombohedral IV-VI material, GeTe. This induces extremely soft optical modes at the zone center, which increase anharmonic acoustic-optical coupling and decrease phonon lifetimes at all frequencies. We predict that PbTe, Pb(Se,Te) and (Pb,Ge)Te alloys driven close to the phase transition in the described manner will have considerably lower lattice thermal conductivity than that of PbTe (by a factor of 2-3). The proposed concept may open new opportunities for the development of more efficient thermoelectric materials.