Towards a better understanding of the unique ultra-low thermal conductivity in SnSe thermoelectric from constraints of its bond anharmonicit

SnSe is a new key thermoelectric material that exhibits an ultra-low lattice thermal conductivity. This is a unique phenomenon among reported TE materials; however, its origin remains highly debated. Several scenarios have been proposed among the most likely one, but not completely accepted, relates the low κT to a highly anisotropy in the phonon scattering. This may be related to the Sn–Se bond anharmonicity and anisotropy. This kind of information with a local character and dependence on the solid's vibrational properties could be only accessed by spectroscopies at local-range, as the case of EXAFS or Raman. We propose to study the bond anharmonicity and anisotropy in binary SnSe using high-quality EXAFS under isobaric condition in DAC and cryostat from 2 to 300 K at HP (100 GPa). These data will improve our knowledge on the features of the intrinsic low thermal conductivity in SnSe at non-ambient conditions and will have a high impact for further developments in thermoelectrics.

SnSe（硒化锡）是一种新型关键热电材料，展现出超低的晶格热导率。该现象在已公开报道的热电（TE, Thermoelectric）材料中颇为独特，但其成因仍存在广泛争议。目前已提出多种相关假说，其中最具说服力的一种尚未得到完全认可——该假说将低的热导率κ_T与声子散射的高度各向异性联系起来，而这一关联可能源于Sn-Se键的非简谐性与各向异性。这类具备局域特性且依赖于固体振动性质的信息，仅能通过局域尺度的光谱技术获取，例如扩展X射线吸收精细结构谱（EXAFS, Extended X-ray Absorption Fine Structure）或拉曼光谱（Raman）。本研究拟采用高质量的扩展X射线吸收精细结构谱，在100 GPa的高压（HP, High Pressure）环境下，借助金刚石对顶砧（DAC, Diamond Anvil Cell）与低温恒温器，在等压条件下对2至300 K温度区间内的二元硒化锡中的键合非简谐性与各向异性开展研究。相关实验数据将深化我们对非环境条件下硒化锡本征低热导率特性的认知，并将对热电领域的后续发展产生重要影响。