Role of Self-Organization, Nanostructuring, and Lattice Strain on Phonon Transport in NaPb_18-xSn_xBiTe₂₀ Thermoelectric Materials

Abstract

The composition and microstructure of five thermoelectric materials, PbTe, SnTe, Pb(0.65)Sn(0.35)Te and NaPb(18-x)Sn(x)BiTe(20) (x = 5, 9), were investigated by advanced transmission electron microcopy. We confirm that the pure PbTe, SnTe, and Pb(0.65)Sn(0.35)Te have a uniform crystalline structure and homogeneous compositions without any nanoscale inclusions. On the other hand, the nominal NaPb(9)Sn(9)BiTe(20) phase contains extensive inhomogeneities and nanostructures with size distribution of 3-7 nm. We find that the chemical architecture of the NaPb(13)Sn(5)BiTe(20) member of the series to be more complex; besides nanoscale precipitates, self-organized lamellar structures are present which were identified as PbTe and SnTe by composition analysis and transmission electron microscopy image simulations. Density functional theory calculations suggest that the arrangement of the lamellar structures conforms to the lowest total energy configuration. Geometric-phase analyses revealed large distributed elastic strain around the nanoscale inclusions and lamellar structures. We propose that interface-induced elastic perturbations in the matrix play a decisive role in affecting the phonon-propagation pathways. The interfaces further enhance phonon scattering which, in turn, reduces the lattice thermal conductivity in these systems that directly results directly in improvement in the thermoelectric figure of merit.

Nanodopant-Induced Band Modulation inAgPbmSbTe2+m-Type Thermoelectrics

“…A hallmark of semiconductor physics is effective modulation of electronic structure and transport properties by doping [1]; however, the impact of nanoscale dopants remains largely unknown. Recent advances on doped lead chalcogenides show that superior thermoelectric (TE) figure of merit ZT = S 2 σT /(κ e + κ p ) can be achieved when such nanodopants are introduced [2][3][4][5][6][7][8][9][10]. Here, S, σ, T , κ e , and κ p are thermopower, electrical conductivity, absolute temperature, electron, and lattice thermal conductivity, respectively.…”

Thermoelectric Properties of Alumina-Doped Bi0.4Sb1.6Te3 Nanocomposites Prepared through Mechanical Alloying and Vacuum Hot Pressing

“…Advances in ZT can be achieved through considerable reductions in thermal conductivities through phonon scattering. Incorporating nanoparticles into TE materials to act as additional phonon scattering sites inside the grain boundary or matrix regions has recently been demonstrated effectively increase ZT [27][28][29]. According to this approach, for nano-and microstructured TE composite materials shown in Figure 4, the dispersed γ-Al 2 O 3 nanoparticles are expected to create an additional grain boundary and interfacial area, which increases phonon scattering and decreases thermal conductivity.…”

Electron Microscopy for Characterization of Thermoelectric Nanomaterials

“…Detailed sample preparation of doped PbTe [83,84], PbTe + XTe (X ¼ Mg, Ca, Sr, Ba, Cd) [32,[40][41][42][43][44], PbTe + PbS [33,[45][46][47], PbTe + PbSnS 2 [48,49], PbTe + X (X ¼ Pb, Sb, Bi, Si/Ge) [34,35,85,86], TAGS [87], LAST(T) [88], SALT [89,90], and PbTe-Sb 2 Te 3 [91] can be found in corresponding literatures, which will be discussed in the following sections.…”

“…Figure 10.47f, g displays strain maps along the 001 and 110 directions, respectively. Correspondingly, three distinct regions show different strain information: For the amorphous region, the irregular contrast represents damage from the ion beam thinning; for the lamellar structure region, [90] a separation of about 6 % off between PbTe and SnTe along [100] was observed, while uniform contrast along [110]; for the nonlamellar structure region, homogeneous contrast was observed. These findings signify that SnTe is highly distorted at the interfaces.…”