Understanding Phonon Scattering by Nanoprecipitates in Potassium-Doped Lead Chalcogenides

Abstract

We present a comprehensive experimental and theoretical study of phonon scattering by nanoprecipitates in potassium-doped PbTe, PbSe, and PbS. We highlight the role of the precipitate size distribution measured by microscopy, whose tuning allows for thermal conductivities lower than the limit achievable with a single size. The correlation between the size distribution and the contributions to thermal conductivity from phonons in different frequency ranges provides a physical basis to the experimentally measured thermal conductivities, and a criterion to estimate the lowest achievable thermal conductivity. The results have clear implications for efficiency enhancements in nanostructured bulk thermoelectrics.

Silver content dependent thermal conductivity and thermoelectric properties of electrodeposited antimony telluride thin films

“…In crystalline structures, Umklapp scattering dominates the phonon transport at the temperature range of interest, which shortens the phonon mean free path and leads to a reduction in the thermal conductivity with the temperature. The thermal conductivity of crystalline samples κ C is computed using the Callaway model 44 , which is expressed aswhere the average phonon relaxation time τ is computed combining phonon-grain boundary , film boundaries , phonon-impurity , Umklapp , phonon-carrier , and, in the case of Ag 3.9 Sb 33.6 Te 62.5 films, nanoprecipitate scattering mechanisms as 45–47 , where D is the average grain size , P is the phonon transmission across the grain boundary, t is the thickness of the film, n NP is the nanoprecipitate number density, and Θ is the average nanoprecipitate scattering cross-section, which is estimated using the average nanoinclusion size, and the mass and tensor strength difference with the matrix 17,48 . As detailed at the beginning of this section, the thickness of the film is measured using cross-sectional SEM imaging and the grain size is derived from the XRD spectra.…”

“…11 reached a zT of 1.4 at 550 K after doping AgSbTe 2 with 2% Se. Concentrations of silver lower than the stoichiometry can produce impurities in the matrix or form precipitates, both of which are favorable to reduce the thermal conductivity 17,18 . In particular, Sb 2 Te 3 /Ag 2 Te composites fabricated using ball milling have been found to improve the zT up to 1.5 at 700 K, and AgSbTe 2 /Ag 2 Te quenched ingots reached 1.5 at 500 K 19 .…”

Designing efficient spin Seebeck-based thermoelectric devices via simultaneous optimization of bulk and interface properties

“…For the NFO samples, we can estimate y by investigating which regime is more influential compared to the other, and thus closely examine t np À1 as follows. In the long-wavelength limit (w { 1), it has been shown [51][52][53] that mass density and force constant differences between nano-precipitates and host matrix play an important role in determining y. Our nano-NFO precipitates have almost identical structure and composition with those of the NFO matrix.…”

Seeing Structural Mechanisms of Optimized Piezoelectric and Thermoelectric Bulk Materials through Structural Defect Engineering

“…In addition, Bi nanoprecipitates can not only release the strain between the mismatched grains, but can also further promote charge redistribution as additional carriers, which are parallel to the result of modulated doping [21,22,165,166]. (PbQ, Q = Te, Se and S) thermoelectrics [13,14,164,168,169]. These nanostructures are thought to be inherent, which comes from the inevitable evaporation of lead during its formation process.…”

“…Such atomic-scale 2D planes of crystal mismatches densely pack together to form a 3D strain network, which is an effective scattering source for phonons with short to medium wavelengths. Furthermore, another type of planar defect, platelet-like precipitates with one/two atom-layer thickness, are characteristic nanostructures in lead chalcogenide (PbQ, Q = Te, Se and S) thermoelectrics [13,14,164,168,169]. These nanostructures are thought to be inherent, which comes from the inevitable evaporation of lead during its formation process.…”