Comparison of the electronic and thermoelectric properties of three layered phases Bi2Te3, PbBi2Te4 and PbBi4Te7: LEGO thermoelectrics

Abstract

The electronic and thermoelectric properties of Bi2Te3, PbBi2Te4 and PbBi4Te7 were examined on the basis of density functional theory (DFT) calculations and thermoelectric transport property measurements. The layered phase PbBi4Te7 is composed of the slabs forming the layered phases Bi2Te3 and PbBi2Te4. The electronic structure of PbBi4Te7 around the valence band maximum and conduction band minimum exhibits those of Bi2Te3 and PbBi2Te4. The band gap of PbBi4Te7 lies in between those of Bi2Te3 and PbBi2Te4, and the density of states of PbBi4Te7 is well approximated by the sum of those of Bi2Te3 and PbBi2Te4. In terms of the carrier concentration, the carrier mobility, the carrier lifetime, the electrical conductivity normalized to the carrier lifetime, and the effective mass, the layered phases Bi2Te3, PbBi4Te7 and PbBi2Te4 form a group of thermoelectrics, which have the structures composed of several different slabs and whose thermoelectric properties are approximated by the average of those of the constituent slabs. We propose to use the term “LEGO thermoelectrics” to describe such a family of thermoelectric materials that operate in a desired temperature range and possess predictable thermoelectric properties.

Achieving an Ultrahigh Power Factor in Sb2Te2Se Monolayers via Valence Band Convergence

“…What turns this family into outstanding and the most studied TE materials, ,,− beside low lattice thermal conductivity, is their excellent electronic transport properties and a relatively high PF compared to those of other single-layer TE candidates. The feature in the band structure of these monolayers that enhances their PF is the high band degeneracy N v and nonparabolic band structure near the valence band maximum (VBM). ,, Regardless of band alignment and height of valleys, in these family of materials, the dispersion shape around the Γ point is still similar to that of Bi 2 Te 3 and Bi 2 Se 3 in which the energy–momentum relation shows a “Mexican hat” dispersion causing a large enhancement of PF and zT .…”

“…From the comparison with experimental data at 300 K, Hinsche et al determined that the in-plane τ = 1.2 × 10 –14 and 1.1 × 10 –14 s for the Sb 2 Te 3 and Bi 2 Te 3 , respectively. Also, fitted values such as 2.2 × 10 –14 , and ≈0.65 × 10 –14 s were suggested for Bi 2 Te 3 at 300 K. Likewise, for Bi 2 Te 2 S, the in-plane relaxation time of 3 × 10 –14 s was used …”

Thermoelectric Transport Properties of Pb(Bi1-xSnx)2Te4 (0≤x≤1) compounds

“…Tetradymite(TD) 구조의 칼코겐화물은 우수한 열전성능 으로 인하여 그동안 많은 관심을 받아왔다 [1][2][3][4][5]. TD 구 조에서는 화합물을 이루는 각 원소의 단원자층이 c-축 방 향으로 rhombohedral 구조(R-3m)를 이루면서 적층된다 [6][7][8][9]. 가장 단순한 TD 구조인 M V 2 Ch VI 3 (여기서 M V = Bi, Sb, 그리고 Ch VI = S, Se, Te)는 각 단원자층이 5층으 로 적층된 구조 (quintuple monoatomic layers, QML)를 이룬다 [6][7][8][9].…”

“…TD 구 조에서는 화합물을 이루는 각 원소의 단원자층이 c-축 방 향으로 rhombohedral 구조(R-3m)를 이루면서 적층된다 [6][7][8][9]. 가장 단순한 TD 구조인 M V 2 Ch VI 3 (여기서 M V = Bi, Sb, 그리고 Ch VI = S, Se, Te)는 각 단원자층이 5층으 로 적층된 구조 (quintuple monoatomic layers, QML)를 이룬다 [6][7][8][9]. 이때 QML의 각 단원자층 사이에 존재하는 van der Waals gap으로 인하여 낮은 열전도도를 나타내는 데, 특히 Bi 2 Te 3 계 화합물은 낮은 bandgap 에너지로 인하 여 상온 근처의 온도에서 우수한 열전특성을 나타내는 대 표적 열전소재이다 [1,10,11].…”

“…가진다[9,14]. 최근 들어서 Lee 등은 QML과 SML이 교 대로 적층된 PbBi 4 Te 7 에서 전하농도, carrier lifetime, 유효 질량 등 전하 및 열전 수송현상의 주요 인자가 QML로 이루어진 Bi 2 Te 3 와 SML로 이루어진 PbBi 2 Te 4 의 평균값에 근사하다는 것을 실험과 이론으로 밝힌 바 있으며, 이러한 bl o ck 간의 조합에 따른 열전특성 제어를 L E G O thermoelectrics로 명명하였다 [9].…”