Microstructure‐Lattice Thermal Conductivity Correlation in Nanostructured PbTe_0.7S_0.3 Thermoelectric Materials

Abstract

The reduction of thermal conductivity, and a comprehensive understanding of the microstructural constituents that cause this reduction, represent some of the important challenges for the further development of thermoelectric materials with improved figure of merit. Model PbTe‐based thermoelectric materials that exhibit very low lattice thermal conductivity have been chosen for this microstructure–thermal conductivity correlation study. The nominal PbTe0.7S0.3 composition spinodally decomposes into two phases: PbTe and PbS. Orderly misfit dislocations, incomplete relaxed strain, and structure‐modulated contrast rather than composition‐modulated contrast are observed at the boundaries between the two phases. Furthermore, the samples also contain regularly shaped nanometer‐scale precipitates. The theoretical calculations of the lattice thermal conductivity of the PbTe0.7S0.3 material, based on transmission electron microscopy observations, closely aligns with experimental measurements of the thermal conductivity of a very low value, ∼0.8 W m−1 K−1 at room temperature, approximately 35% and 30% of the value of the lattice thermal conductivity of either PbTe and PbS, respectively. It is shown that phase boundaries, interfacial dislocations, and nanometer‐scale precipitates play an important role in enhancing phonon scattering and, therefore, in reducing the lattice thermal conductivity.

Thermoelectric performance of tellurium-reduced quaternary p-type lead–chalcogenide composites

“…These results denote that phonon scattering has occurred due to disorder rising from solute atoms in solid solution as discussed above, and also through interfaces of the lamellar pattern. Although the interlamellar spacing has been increased by equilibration at high temperatures, compared to previous studies, 17 phonon scattering by boundaries and interfaces played a significant role in the thermal conductivity reduction.…”

“…Recent studies 7-9 11 12 have improved PbTe thermoelectric performance significantly through tuning the electronic structure and/or nanostructuring of bulk materials. However, Te is rare in the Earth's crust, used in other applications 13 and is expensive hence the focus in the latest studies [14][15][16][17] trying to replace Te with Se or S. 18 19 Sulphur is amongst the 16 most abundant elements in the Earth's crust 13 and replacing Te, partially with S also provides a fascinating opportunity to form fine lamellar microstructure through spinodal decomposition, which appears in binary phase diagrams of the PbTe-PbS system. Lamellar patterns resembling a eutectic structure have been demonstrated for several thermoelectric materials 17 20-22 and thermal conductivity reduction has been reported, specifically for PbTe-PbS system, 14 …”

Phonon conduction in PbSe, PbTe, and PbTe1−xSexfrom first-principles calculations

“…Most of the recent experimental studies on the strong reduction of the lattice thermal conductivity in nanostructured PbTe [9,10] emphasized the importance of dislocations, nanoscale precipitates and strain while pointing out that the mere presence of nanostructuring cannot sufficiently increase the phonon scattering. He et al [11] found that not all nanostructures favorably scatter phonons.…”

“…Significant efforts have been made to enhance the zT value of PbTe [2][3][4][5][6][7][8][9][10][11]. By introducing resonant states, Tl doped p-type PbTe resulted in a high zT value of 1.5 at 773 K [4].…”

Chemical composition tuning in quaternary p-type Pb-chalcogenides – a promising strategy for enhanced thermoelectric performance

“…[13][14][15][16] Ternary PbTe-rich alloys of PbTe-PbSe 4,17,18 show a higher figure of merit than individual binary PbTe and PbSe systems in the temperature range of 550-800 K, mainly due to alteration of the electronic band structure. 4,18 In contrast, higher zT values of PbTe-PbS [19][20][21][22] compared to the binary systems are credited to the reduction in lattice thermal conductivity, which originates from phonon scattering at the interfaces of secondary phases, as PbS shows very limited solubility in the PbTe matrix. 23 Here, we present a strategy to design single-phase quaternary alloys with high thermoelectric efficiency.…”