Ultralow thermal conductivity from transverse acoustic phonon suppression in distorted crystalline \u03b1-MgAgSb

Xiyang Li,Kazutaka Ikeda,Lunhua He,Enyue Zhao,Zhifeng Ren,Huaizhou Zhao,Zhigang Zhang,Maiko Kofu,Yang Ren,Tatiana Guidi,Manh Duc Le,Bao-Tian Wang,Maxim Avdeev,Xun-Li Wang,Peng-Fei Liu,Toshiya Otomo,Kenji Nakajima,Fangwei Wang,Jie Chen

doi:10.1038/s41467-020-14772-5

Abstract

Low thermal conductivity is favorable for preserving the temperature gradient between the two ends of a thermoelectric material, in order to ensure continuous electron current generation. In high-performance thermoelectric materials, there are two main low thermal conductivity mechanisms: the phonon anharmonic in PbTe and SnSe, and phonon scattering resulting from the dynamic disorder in AgCrSe2 and CuCrSe2, which have been successfully revealed by inelastic neutron scattering. Using neutron scattering and ab initio calculations, we report here a mechanism of static local structure distortion combined with phonon-anharmonic-induced ultralow lattice thermal conductivity in α-MgAgSb. Since the transverse acoustic phonons are almost fully scattered by the compound’s intrinsic distorted rocksalt sublattice, the heat is mainly transported by the longitudinal acoustic phonons. The ultralow thermal conductivity in α-MgAgSb is attributed to its atomic dynamics being altered by the structure distortion, which presents a possible microscopic route to enhance the performance of similar thermoelectric materials.

Highlights

Low thermal conductivity is favorable for preserving the temperature gradient between the two ends of a thermoelectric material, in order to ensure continuous electron current generation
We use neutron scattering measurements together with systematic ab initio simulations to study the crystalline structure and the atomic dynamics of two α-MgAgSb-based materials, MgAg0.97Sb0.99 and MgAg0.965Ni0.005Sb0.99, the α-phase of which exhibits the highest thermoelectric performance[32]. We find that their ultralow κlat is induced both by static local structure distortion suppression of the transverse acoustic phonons and the phonon anharmonicity
The distorted structure has a significant phonon scattering effect and the complex primitive unit cell has a large ratio of optical phonon branches (69/72) that significantly reduces κlat[17], since acoustic phonons are the main contributor to κlat[1,6,20]

Summary

Introduction

Low thermal conductivity is favorable for preserving the temperature gradient between the two ends of a thermoelectric material, in order to ensure continuous electron current generation. We use neutron scattering measurements together with systematic ab initio simulations to study the crystalline structure and the atomic dynamics of two α-MgAgSb-based materials, MgAg0.97Sb0.99 and MgAg0.965Ni0.005Sb0.99 (the sample of Ni ptype substitution for Ag has a higher anomalous electrical resistivity15), the α-phase of which exhibits the highest thermoelectric performance[32]. We find that their ultralow κlat is induced both by static local structure distortion suppression of the transverse acoustic phonons and the phonon anharmonicity

Methods

Results

Conclusion