High thermoelectric performance in metallic NiAu alloys

TL;DR

This paper demonstrates that metallic NiAu alloys can achieve record-high thermoelectric performance by tuning electronic scattering, challenging the notion that metals are poor thermoelectrics and opening new avenues for high-efficiency TE materials.

Contribution

The study introduces a novel approach to enhance thermoelectric performance in metals by engineering energy-dependent scattering, with experimental validation in NiAu alloys showing record power factors and figure of merit.

Findings

Colossal power factors up to 34 mW/mK^2 in NiAu alloys.

Achieved a figure of merit (zT) up to 0.5, a record for metals.

Demonstrated high thermoelectric efficiency in metallic alloys.

Abstract

Thermoelectric (TE) materials seamlessly convert thermal into electrical energy and vice versa, making them promising for applications such as power generation or cooling. Although historically the TE effect was first discovered in metals, state-of-the-art research mainly focuses on doped semiconductors with large figure of merit, $zT$, that determines the conversion efficiency of TE devices. While metallic alloys have superior functional properties, such as high ductility and mechanical strength, they have mostly been discarded from investigation in the past due to their small Seebeck effect. Here, we realize unprecedented TE performance in metals by tuning the energy-dependent electronic scattering. Based on our theoretical predictions, we identify binary NiAu alloys as promising candidate materials and experimentally discover colossal power factors up to 34 mWm$^{-1}$K$^{-2}$ (on average 30 mWm$^{-1}$K$^{-2}$ from 300 to 1100 K), which is more than twice larger than in any known bulk material above room temperature. This system reaches a $zT$ up to 0.5, setting a new world record value for metals. NiAu alloys are not only orders of magnitude more conductive than heavily doped semiconductors, but also have large Seebeck coefficients originating from an inherently different physical mechanism: within the Au s band conduction electrons are highly mobile while holes are scattered into more localized Ni d states, yielding a strongly energy-dependent carrier mobility. Our work challenges the common belief that good metals are bad thermoelectrics and presents an auspicious paradigm for achieving high TE performance in metallic alloys through engineering electron-hole selective s-d scattering.