Designing chemical analogs to PbTe with intrinsic high band degeneracy and low lattice thermal conductivity

Chris Wolverton,S Shahab Naghavi,Yi Xia,Vidvuds Ozoliņš,Jiangang He

doi:10.1038/s41467-019-08542-1

Abstract

High-efficiency thermoelectric materials require simultaneously high power factors and low thermal conductivities. Aligning band extrema to achieve high band degeneracy, as realized in PbTe, is one of the most efficient approaches to enhance power factor. However, this approach usually relies on band structure engineering, e.g., via chemical doping or strain. By employing first-principles methods with explicit computation of phonon and carrier lifetimes, here we show two full-Heusler compounds Li2TlBi and Li2InBi have exceptionally high power factors and low lattice thermal conductivities at room temperature. The expanded rock-salt sublattice of these compounds shifts the valence band maximum to the middle of the Σ line, increasing the band degeneracy by a factor of three. Meanwhile, resonant bonding in the PbTe-like sublattice and soft Tl–Bi (In–Bi) bonding interaction is responsible for intrinsic low lattice thermal conductivities. Our results present an alternative strategy of designing high performance thermoelectric materials.

Highlights

High-efficiency thermoelectric materials require simultaneously high power factors and low thermal conductivities
Our density functional theory (DFT) calculations show that FH Li2TlBi is on the T = 0 K convex hull, which means it is thermodynamically stable at zero Kelvin, and Li2InBi is just 4 meV/atom above the convex hull, which indicates it is thermodynamically weakly unstable
The convex hull distance is the formation energy difference between the target compound and its competing phases included in the Open Quantum Material Database (OQMD)[18], which contains over

Summary

Introduction

High-efficiency thermoelectric materials require simultaneously high power factors and low thermal conductivities. Aligning band extrema to achieve high band degeneracy, as realized in PbTe, is one of the most efficient approaches to enhance power factor. This approach usually relies on band structure engineering, e.g., via chemical doping or strain. By employing first-principles methods with explicit computation of phonon and carrier lifetimes, here we show two full-Heusler compounds Li2TlBi and Li2InBi have exceptionally high power factors and low lattice thermal conductivities at room temperature. Efficient TE materials are required for practical applications and are characterized by the figure of merit zT = (S2σT)/(κL + κe), where S, σ, κe, κL, and T are the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, lattice thermal conductivity, and temperature, respectively. Take the well studied TE material PbTe (rock-salt lattice, space group Fm3m) as an example, once the second maximum of the valence band (the middle of the Σ line, multiplicity is 12) is converged with the valence band maximum (VBM) (at the L point, multiplicity is 4) by alloying an appropriate amount PbSe, a significant enhancement of zT from 0.8 to

Methods

Results

Conclusion