Grain Boundary Engineering for Achieving High Thermoelectric Performance in n‐Type Skutterudites

Abstract

Grain or phase boundaries play a critical role in the carrier and phonon transport in bulk thermoelectric materials. Previous investigations about controlling boundaries primarily focused on the reducing grain size or forming nanoinclusions. Herein, liquid phase compaction method is first used to fabricate the Yb‐filled CoSb3 with excess Sb content, which shows the typical feature of low‐angle grain boundaries with dense dislocation arrays. Seebeck coefficients show a dramatic increase via energy filtering effect through dislocation arrays with little deterioration on the carrier mobility, which significantly enhances the power factor over a broad temperature range with a high room‐temperature value around 47 μW cm−2 K−1. Simultaneously, the lattice thermal conductivity could be further suppressed via scattering phonons via dense dislocation scattering. As a result, the highest average figure of merit ZT of ≈1.08 from 300 to 850 K could be realized, comparable to the best reported result of single or triple‐filled Skutterudites. This work clearly points out that low‐angle grain boundaries fabricated by liquid phase compaction method could concurrently optimize the electrical and thermal transport properties leading to an obvious enhancement of both power factor and ZT.

Superstrengthening Bi2Te3 through Nanotwinning

“…In addition, nanotwins in ceramics have been found to dramatically enhance the hardness of diamond and boron nitride [23,24]. However, the influence of nanotwins on the mechanical properties of TE semiconductors remains largely unexplored.Very recently, a GBs' engineering strategy was proposed to reduce the lattice thermal conductivity and thereby significantly enhance the zT value of TE semiconductors [25][26][27][28]. In particular, the dense dislocation arrays formed at low-energy GBs from liquid-phase compaction in bismuth telluride based TE materials has been demonstrated to dramatically decrease the thermal conductivity…”

“…Very recently, a GBs' engineering strategy was proposed to reduce the lattice thermal conductivity and thereby significantly enhance the zT value of TE semiconductors [25][26][27][28]. In particular, the dense dislocation arrays formed at low-energy GBs from liquid-phase compaction in bismuth telluride based TE materials has been demonstrated to dramatically decrease the thermal conductivity…”

Micro- and Macromechanical Properties of Thermoelectric Lead Chalcogenides

“…Figure 3(a) shows the tensile-stress -tensile-strain relations. The lowest ideal tensile strength is found to be 5.55 GPa at 0.138 tensile strain along the [100] direction, which is lower shows an obvious 'yielding' process, which is similar to shearing along the (001)/<100> direction as discussed above, while tensions along both the [1][2][3][4][5][6][7][8][9][10] and [111] directions show a sudden drop in tensile stress. We extracted the structural and bond length changes at critical tensile strains to determine the bond-responding processes, as displayed in Figure 3 …”

“…We considered three typical tensile systems, [100], [1][2][3][4][5][6][7][8][9][10], and [111] with supercells containing 64, 48, and 48 atoms, respectively. Figure 3(a) shows the tensile-stress -tensile-strain relations.…”

“…1 Indeed the past two decades has seen dramatic enhancements in the TE figure of merit, zT = α 2 σ/κ, of various materials, achieved through simultaneously optimizing the power factor (α 2 σ) and reducing the thermal conductivity 2 for such materials as PbTe, [3][4][5] skutterudite CoSb 3 , [6][7][8] Bi 2 Te 3 , 9-11 Mg 2 Si, [12][13] and half-Heusler alloys. 14,15 However, despite the improved efficiencies, applications of these TE materials usually impose a severe cyclic temperature gradients that can generate cracks in the microstructure.…”