Peierls distortion as a route to high thermoelectric performance in In4Se3-δ crystals

Thermoelectric materials via Peierls distortion Thermoelectric materials, which convert heat into electricity, are much studied for their potential in energy-saving applications — for example as a way of recovering waste heat in cars. At present, though, these materials are inefficient, with very few of them achieving a thermoelectric figure of merit ( ZT ) above one in the mid-temperature range (500–900 K). Now a figure of merit of 1.48, notably high for a bulk material, is reported for indium selenide crystals (In 4 Se 3–δ ) at 705 K. The high thermoelectric performance of this material is related to a Peierls distortion of the crystal lattice at 710 K. This work suggests a new direction in the search for high-performance thermoelectric materials, exploiting intrinsic nanostructural bulk properties induced by charge density waves. Thermoelectric materials, which can convert heat into electricity, are of great interest for energy sustainability. The problem is the low efficiency of these materials, quantified by a coefficient, ZT , which for mid-temperature materials is usually around 1. The realization of a material, In 4 Se 3–δ , which achieves the ZT value of 1.48 at 705 K, could open up a new avenue in the research to generate high ZT materials. Thermoelectric energy harvesting—the transformation of waste heat into useful electricity—is of great interest for energy sustainability. The main obstacle is the low thermoelectric efficiency of materials for converting heat to electricity, quantified by the thermoelectric figure of merit, ZT . The best available n-type materials for use in mid-temperature (500–900 K) thermoelectric generators have a relatively low ZT of 1 or less, and so there is much interest in finding avenues for increasing this figure of merit 1 . Here we report a binary crystalline n-type material, In 4 Se 3- δ , which achieves the ZT value of 1.48 at 705 K—very high for a bulk material. Using high-resolution transmission electron microscopy, electron diffraction, and first-principles calculations, we demonstrate that this material supports a charge density wave instability which is responsible for the large anisotropy observed in the electric and thermal transport. The high ZT value is the result of the high Seebeck coefficient and the low thermal conductivity in the plane of the charge density wave. Our results suggest a new direction in the search for high-performance thermoelectric materials, exploiting intrinsic nanostructural bulk