Structural and electronic transport properties of polycrystalline p-type CoSb3

Abstract

The structural and electronic transport properties of polycrystalline p-type CoSb3 with different grain sizes (about 3 and 3×102 μm) were investigated. The magnetic susceptibility was also measured. Samples were characterized by x-ray diffractometry, electron-probe microanalysis, and optical microscope observation. Samples were found to be stoichiometric and homogeneous. The Hall carrier concentration of the samples is of the order of 1018 cm−3 and weakly dependent on the temperature. The temperature dependence of the Hall mobility suggests that the predominant scattering mechanism drastically changes depending on grain size: for large grain size a combination of the neutral impurity scattering and the acoustic phonon scattering, and for small grain size the ionized impurity scattering. The magnetic susceptibility was found to be essentially diamagnetic independently of grain size, and to vary slightly with temperature. The weak temperature dependence of the susceptibility can be explained by taking into account the three contributions of ion cores, conduction electrons, and trace amounts of magnetic impurities. From the analysis of the susceptibility due to conduction electrons, the band gap energy was determined to be about 70–80 meV, consistent with a recent band structure calculation. Although the effects of nonmagnetic impurity phases segregated (Sb, etc.) on the scattering mechanism are not clear, the grain size is one of the key factors determining the transport properties of polycrystalline CoSb3.

Lattice dynamics in the FeSb3skutterudite

“…1 were obtained on a sample free of cracks at the ∼50 nm level. Such a dependence of the resistivity on the microstructure has also been observed 27 in polycrystalline CoSb 3 , with reported resistivities of undoped samples between 7 and 1000 μ m at room temperature. [27][28][29][30][31][32][33] The 300 K resistivity of 29.4(1) μ m observed for crack-free FeSb 3 is similar to the 37 μ m of a polycrystalline, sintered, CoSb 3 sample, 30 which also exhibits the temperature dependence of a typical semiconductor.…”

The Impact of Nanostructuring on the Thermal Conductivity of Thermoelectric CoSb3

“…[8] Nanostructured materials exhibit different properties from those of the corresponding bulk substances, single crystals, coarse-grained polycrystals, and glasses, although they have an identical chemical composition. The decrease in the grain size of the material building blocks in the nanometer range leads to a drastic increase in the density of grain boundaries, reaching typical densities of 10 19 interfaces per cubic centimeter. Due to their excess free volume, the grain boundaries in nanocrystalline materials cause large changes in the physical properties compared with large (micrometer-sized) polycrystals.…”

“…The thermal conductivity of CoSb 3 single crystals is about 10 W m ±1 K ±1 at 293 K, and it can be expected that fine grained CoSb 3 materials could have lower k. There are several studies of the grain-size effects on the transport properties of micrometer-size polycrystalline CoSb 3 . [19±21] Anno et al [19] studied the electronic transport properties of polycrystalline CoSb 3 with grain sizes of 3 and 300 lm and reported a drastic change of the predominant scattering mechanism depending on the grain size. Nakagawa et al [21] investigated hot-pressed CoSb 3 samples with grain sizes varying from 1 lm to 40 lm, and reported a value of k = 4.19 W m ±1 K ±1 at 293 K, which is about 40 % of that of the single crystal.…”

Thermoelectric Properties of Half-Heusler TiCoSb Synthesized by Mechanical Alloying Process

“…Indeed, it is possibly attributed to the lower Seebeck coefficient which is caused by the formation of 2 nd phase. 9) Hall mobility seems to be quite low, which might be attributed to the relatively high carrier concentration, leading to the lower value of Seebeck coefficient, 6) as shown in Table 1. Thus, it can be expected that MAed single phase might show much higher ZT values, if it could be obtained via excess Ti addition and other methods.…”