Intrinsically Low Thermal Conductivity and High Carrier Mobility in Dual Topological Quantum Material, n‐Type BiTe

Abstract

A challenge in thermoelectrics is to achieve intrinsically low thermal conductivity in crystalline solids while maintaining a high carrier mobility (μ). Topological quantum materials, such as the topological insulator (TI) or topological crystalline insulator (TCI) can exhibit high μ. Weak topological insulators (WTI) are of interest because of their layered hetero‐structural nature which has a low lattice thermal conductivity (κlat). BiTe, a unique member of the (Bi2)m(Bi2Te3)n homologous series (m:n=1:2), has both the quantum states, TCI and WTI, which is distinct from the conventional strong TI, Bi2Te3 (where m:n=0:1). Herein, we report intrinsically low κlat of 0.47–0.8 W m−1 K−1 in the 300–650 K range in BiTe resulting from low energy optical phonon branches which originate primarily from the localized vibrations of Bi bilayer. It has high μ≈516 cm2 V−1 s−1 and 707 cm2 V−1 s−1 along parallel and perpendicular to the spark plasma sintering (SPS) directions, respectively, at room temperature.

Low-temperature transport properties of n-type layered homologous compounds Bi8−xSbxSe7

“…This temperature dependence and the relatively low values are characteristic of compensated semiconductors observed in both narrow-band-gap semiconductors and semi-metals. While these results are consistent with those obtained for BiSe and for several compounds in the closely-related homologous series (Bi2)n(Bi2Te3)m, 39,48,50 these ( ) data differ from those reported for Bi8Se9 for which, a metallic character is maintained up to 700 K. The comparison between these three compounds shows that the details of the electronic band structure and notably, the possible narrow band gap is sensitive to the stacking sequence. 38 The substitution of Sb for Bi does not significantly modify the temperature dependence that characterizes the binary compound, which persists across the entire Sb concentration range.…”

Slowing down the heat in thermoelectrics

“…The color refers to the mode‐ and frequency‐dependent contributions of Bi and Te atoms. Reproduced with permission from Reference 262. Copyright 2020, Wiley‐VCH.…”

Microscopic mechanism of unusual lattice thermal transport in TlInTe2

“…Crystalline semiconductors with ultralow lattice thermal conductivity (κ l ) are important for effective utilization and management of thermal energy in high-performance thermoelectrics [1][2][3][4] , photovoltaics [5][6][7][8] , thermal barrier coatings 9 , and thermal data storage devices 10 . Although it is quite natural for compounds with complex crystal structures having large unit cells 11,12 and heavy atoms to exhibit low-κ l , relatively simple crystalline materials having small unit cells and even with light atoms 13 could also possess ultralow-κ l due to the presence of rattler atoms 14 , strong lattice anharmonicity [15][16][17][18][19] , or bonding heterogeneity [20][21][22][23] . Investigation of the microscopic mechanism behind the ultralow-κ l that often approaches the glassy limit in ordered compounds is not only fundamentally interesting, but it also helps to unravel the complex correlation between the crystal structure, bonding, and anharmonic lattice dynamics.…”