Effect of Dislocation Arrays at Grain Boundaries on Electronic Transport Properties of Bismuth Antimony Telluride: Unified Strategy for High Thermoelectric Performance

Abstract

Harnessing individual electronic and thermal transport properties selectively has long been a fundamental goal of achieving high thermoelectric (TE) performance in many materials. TE energy conversion efficiency of materials is directly proportional to the material-dependent parameter as known as a dimensionless figure of merit, zT. In principle, twofold intercorrelated relations of physical parameters i) between electrical conductivity (σ) and Seebeck coefficient (S) and ii) between σ and total thermal conductivity (κ total ) in TE semiconductors are strongly correlated each other and the trade-offs have been major obstacles for improving zT, which is determined by zT = S 2 σ T/κ total where T is temperature and κ total consists of the sum of electronic (κ elec ) and lattice (κ latt ) contributions to thermal conductivity.Many efforts have been demonstrated to overcome these long historic cliché issues on thermoelectrics. Concerning about electronic transports, several distinct strategies have been proposed for exclusively enhancing power factor (PF: S 2 σ) by utilizing resonance state in Tl-doped p-type PbTe, [1,2] the convergence of electronic bands, [3] and the doping modulation in nanocomposites. [4] However, these approaches are not widely applicable to all TE materials since the enhancement of PF through such strategies utterly depends on the unique electronic band structure of the individual material. Apart from the optimization of PF, remarkable enhancements of the zT have been achieved mostly due to the reduction of the κ latt via increased phonon scattering utilizing structural defects in nanostructured materials, such as grain boundaries, interfaces, dislocations, and precipitates. [4][5][6][7] Further, efforts to find a new material with intrinsically low thermal conductivity have been devoted. [8][9][10] In fact, little room remains for further reducing κ latt in nanostructured single-phase materials because κ latt cannot be reduced below the amorphous limit, which has been already achieved in the state-of-the-art nanostructured TE materials. Moreover, it has been widely recognized that κ elec cannot be decoupled from σ. However, there is a possibility to reduce the κ elec value by decreasing Lorenz number (L) since L is a band structure-dependent parameter of material but relatively Taming electronic and thermal transport properties is the ultimate goal in the quest to achieve unprecedentedly high performance in thermoelectric (TE) materials. Most state-of-the-art TE materials are inherently narrow bandgap semiconductors, which have an inevitable contribution from minority carriers, concurrently decreasing Seebeck coefficient and increasing thermal conductivity. Nevertheless, the restraint control of minority carrier transport is seldom considered as a key element to enhance the TE figure of merit (zT). Herein, it is verified that the localized dislocation arrays at grain boundaries enable the suppression of minority carrier contribution to electronic transport properties, resulting in an increase ...

(Bi,Sb)2Te3/SiC nanocomposites with enhanced thermoelectric performance: Effect of SiC nanoparticle size and compositional modulation

“…Achieving high ZT values is challenging because of the strong coupling of S, σ, and κ tot (mainly κ e ). Nevertheless, great progress has been made in improving the ZT values using a variety of methods such as nanostructure engineering [8][9][10], electronic band engineering [11][12][13], energy-filtering effect [14][15][16][17], defects engineering [18][19][20][21], as well as seeking or exploring materials with intrinsically low thermal conductivity [22][23][24][25][26].…”

Inorganic thermoelectric materials: A review

“…In this regard, if a nanoscale energy barrier acts as an energy filter at the grain boundaries, then without an energy filter, both the high and low energy carriers pass through the components, consequently, this has no effect on the S total . However, with an energy filter, this allows only the high‐energy carriers to pass and restricts the low‐energy carriers from S total and σ total , hence, S total will be enhanced without much change in the σ total , as depicted in Figure A . For instance, Madavali et al added Y 2 O 3 nanoparticles (NPs) into BiSbTe and formed a nanocomposite via ball milling and spark plasma sintering technique, as depicted in Figure B .…”

“…Recently, Rashad et al obtained an E g of 4.8 eV for n‐ type Bi 2 Te 3 nanoparticles in the presence of Sodium hydroxide (NaOH), which is much higher than the E g of ~0.13 eV for pure Bi 2 Te 3 . Besides, using dislocation arrays at grain boundaries of n‐ type Bi 2 Te 3 is an effective and non‐invasive way to reduce κ t by preventing the contribution of minority carriers to electronic transport properties . For instance, Kim et al used liquid‐phase compaction to form dislocation arrays at low‐energy grain boundaries, via melt‐spun and liquid‐phase sintering process, as depicted in Figure A,B .…”

“…Concurrently, the thermocouple, a building block of TEG, will be used to generate electricity, hence, the thermocouple must be made of materials with high σ, could be defined as: where μ , τ, and m b defines the mobility of charge carriers, carrier relaxation time, and band mass, respectively. For a two carrier transport system, total electrical conductivity, σ total , and Seebeck coefficient, S total , could be defined as: where σ n , σ p, S n , and S p defines σ for n ‐and p ‐type material, and S for n ‐type material, p ‐type material, respectively.…”

Fabrication of PEDOT: PSS-PVP Nanofiber-Embedded Sb2Te3 Thermoelectric Films by Multi-Step Coating and Their Improved Thermoelectric Properties

“…Even though an amorphous Sb 2 Te 3 phase fabricated via an electrochemical process possessed a relatively high S of~500 µV/K at room temperature, it only exhibited very low electrical conductivity (σ,~10 −2 S/cm) [5]. Therefore, to overcome this problem, scientists have modulated various factors, including chemical composition [7], crystal phase [5,8], crystallinity [9], charge-carrier concentration [10], and mobility [11,12].…”