Minimum Thermal Conductivity in Weak Topological Insulators with Bismuth‐Based Stack Structure

Abstract

Contrary to the conventional belief that the consideration for topological insulators (TIs) as potential thermoelectrics is due to their excellent electrical properties benefiting from the topological surface states, this work shows that the 3D weak TIs, formed by alternating stacks of quantum spin Hall layers and normal insulator (NI) layers, can also be decent thermoelectrics because of their focus on minimum thermal conductivity. The minimum lattice thermal conductivity is experimentally confirmed in Bi14Rh3I9 and theoretically predicted for Bi2TeI at room temperature. It is revealed that the topologically “trivial” NI layers play a surprisingly critical role in hindering phonon propagation. The weak bonding in the NI layers gives rise to significantly low sound velocity, and the localized low‐frequency vibrations of the NI layers cause strong acoustic–optical interactions and lattice anharmonicity. All these features are favorable for the realization of exceptionally low lattice thermal conductivity, and therefore present remarkable opportunities for developing high‐performance thermoelectrics in weak TIs.

Unique Role of Refractory Ta Alloying in Enhancing the Figure of Merit of NbFeSb Thermoelectric Materials

“…Strategies for increasing zT have focused on the reduction of the lattice thermal conductivity by hierarchical microstructure, [3,4] nanostructuring [5,6] point defects, [7,8] and the enhancement of the power factor (PF = α 2 σ) by optimal doping and band engineering [9][10][11] as well as the employment of complex crystal structures that possess intrinsically low lattice thermal conductivity. [12][13][14][15][16] Half-Heusler (HH) alloys, with a valence electron count of 8 or 18, have been extensively studied as potential hightemperature TE materials due to their excellent electrical properties, mechanical properties, and high temperature stability. [17][18][19] MNiSn-and MCoSb-based (M = Ti, Zr, Hf) HH alloys are the first two most studied families as n-type materials and p-type materials, respectively.…”

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

“…Conventional topological insulators (TI, where metallic surface states are protected by time reversal symmetry) such as Bi 2 Te 3 and Bi 2 Se 3 and topological crystalline insulators (TCI, where metallic surface states are protected by crystal mirror symmetry) such as SnTe are some of the best known TE materials. A weak topological insulator (WTI, for example, BiSe) arises from stacking of 2D TI layers and exhibits even number of Dirac cones on the side surfaces; its layered hetero‐structure is important to exhibit low κ lat …”

“…[22] Interestingly,s trong spin-orbit coupling in topological materials (TM) facilitates high band degeneracy( N V ), thus high carrier mobility (m) while heavy constituent elements cause slow acoustic waves needed to achieve low k lat .C onventional topological insulators (TI, where metallic surface states are protected by time reversal symmetry) [22][23][24] such as Bi 2 Te 3 and Bi 2 Se 3 and topological crystalline insulators (TCI, where metallic surface states are protected by crystal mirror symmetry) [25][26][27][28] such as SnTea re some of the best known TE materials.Aweak topological insulator (WTI, for example,B iSe) arises from stacking of 2D TI layers and exhibits even number of Dirac cones on the side surfaces;i ts layered hetero-structure is important to exhibit low k lat . [16,29] BiTe, au nique member of the (Bi 2 ) m (Bi 2 Te 3 ) n (where m:n = 1:2) homologous series, [30,31] possesses natural van der Waals hetero-structure (space group P " 3m1), where az igzag Bi-Bi bilayer is sandwiched between Te-Bi-Te-Bi-Teq uintuple layers (QL) via weak van der Waals interactions (Figure 1a). Recently,B iTeh as emerged as ad ual topological insulator, which is af ascinating new quantum material.…”

Измерение Толщины Блочных Пленок Висмута Методом Атомно-Силовой Микроскопии С Применением Избирательного Химического Травления

“…Эта ак-туальность обусловлена размерной зависимостью эф-фектов, исследования которых активно ведутся в на-стоящее время на низкоразмерных структурах системы висмут−сурьма: квантовый размерный эффект, переход полуметалл−полупроводник, увеличение термоэлектри-ческой эффективности в тонкой пленке, состояние топо-логического изолятора и др. [1][2][3][4][5][6][7][8][9].…”