Effect of ZnO and SnO2 Nanolayers at Grain Boundaries on Thermoelectric Properties of Polycrystalline Skutterudites

Abstract

Nanostructuring is considered one of the key approaches to achieve highly efficient thermoelectric alloys by reducing thermal conductivity. In this study, we investigated the effect of oxide (ZnO and SnO2) nanolayers at the grain boundaries of polycrystalline In0.2Yb0.1Co4Sb12 skutterudites on their electrical and thermal transport properties. Skutterudite powders with oxide nanolayers were prepared by atomic layer deposition method, and the number of deposition cycles was varied to control the coating thickness. The coated powders were consolidated by spark plasma sintering. With increasing number of deposition cycle, the electrical conductivity gradually decreased, while the Seebeck coefficient changed insignificantly; this indicates that the carrier mobility decreased due to the oxide nanolayers. In contrast, the lattice thermal conductivity increased with an increase in the number of deposition cycles, demonstrating the reduction in phonon scattering by grain boundaries owing to the oxide nanolayers. Thus, we could easily control the thermoelectric properties of skutterudite materials through adjusting the oxide nanolayer by atomic layer deposition method.

Effect of Powder ALD Interface Modification on the Thermoelectric Performance of Bismuth

“…A negligible change in the S of other thermoelectric materials with an increasing number of ALD cycles of other oxides has been reported before. [ 46 ] As shown in Figure 4b, the σ of coated samples with different oxides dramatically and continuously decreased when the number of ALD cycles increased. For Bi coated with five ALD cycles of TiO 2 and ZnO, this reduction is from ≈5800 (for pure Bi) to ≈3950 and ≈3900 S cm −1 , respectively, demonstrating that the oxide coating has a significant influence on the manipulation of the electrical properties.…”

“…[39,40] Furthermore, because of the controlled layer-by-layer growth, ALD can uniformly coat any structure, from planar substrates to structures, indicating that the ALD deposition process has great potential to extend from the planar substrate to the powder surface. [32,41] Powder ALD (PALD) has already demonstrated unprecedented success in improving the TE performance of various TE materials, such as Bi 2 Te 3 alloys, [42][43][44][45] CoSb 3 , [46] and ZrNiSn-based materials. [47] Bismuth (Bi) was the first elemental metal material to exhibit significant TE effects, but it has been overshadowed by the discovery of bismuth telluride alloys.…”

Water-Free SbOx ALD Process for Coating Bi2Te3 Particles

“…ALD is a well-known deposition method that enables controlled layer-by-layer growth of different materials on planar substrates, as well as threedimensional objects. Powder ALD has already been used to effectively enhance the TE properties of ZrNiSn-based materials [6], CoSb 3 [7], and Bi 2 Te 3 [8][9][10][11] alloys. Total thermal conductivity was suppressed due to the second phase formation and the aforementioned reasons.…”

Surface Modification of Bismuth by ALD of Antimony Oxide for Suppressing Lattice Thermal Conductivity

“…Furthermore, controlled layer-by-layer growth might ensure homogeneous deposition from a planar substrate to a three-dimensional structure and give a fresh insight into the deposition of thin films on the surface of powders . Powder ALD (PALD) has been used effectively in a variety of traditional TE materials systems, such as Bi 2 Te 3 alloys, − CoSb 3 , and ZrNiSn-based materials . In all these investigations, the values of κ tot were unprecedentedly suppressed using TiO 2 /Al 2 O 3 /ZnO coating layers because of their brilliant chemical stability and developed deposition process. ,,,, However, if further suppression of κ tot in TE matrices is desired, one of the main challenges that must be addressed is the development of novel coating layers.…”

“…14 Powder ALD (PALD) has been used effectively in a variety of traditional TE materials systems, such as Bi 2 Te 3 alloys, 15−18 these investigations, the values of κ tot were unprecedentedly suppressed using TiO 2 /Al 2 O 3 /ZnO coating layers because of their brilliant chemical stability and developed deposition process. 14,16,18,19,21 However, if further suppression of κ tot in TE matrices is desired, one of the main challenges that must be addressed is the development of novel coating layers. The deposition of Sb 2 O 5 thin films by ALD technique only was reported using SbCl 5 /water deposited at 773 K and Sb(NMe 2 ) 3 /O 3 deposited at 393 K. 22,23 Herein, by using a new precursors combination of SbCl 5 as antimony reactant and H 2 O 2 as oxidizer, we deposited Sb 2 O 5 at low deposition temperature of 373 K. The uniform amorphous Sb 2 O 5 film was deposited on the Si-SiO 2 wafer as confirmed by scanning electron microscope (SEM), transmission electron microscope (TEM), and grazing incidence X-ray diffraction (GI-XRD), as presented in Figure S1a, b.…”