Effects of Composition and Annealing on the Electrical Properties of CoSb₃

Abstract

A series of CoSb3 samples was synthesized at low temperature (∼150 °C) using modulated elemental reactants, with composition varying between Co-rich and Sb-rich, resulting in lattice parameters ranging from 9.023 to 9.090 Å. The samples were annealed in 100 °C increments from 200 to 600 °C, with lattice parameter, electrical resistivity, and Seebeck coefficient measured after each annealing. The spread of lattice parameters decreased with annealing (9.045 to 9.062 Å). The electrical resistivity of the samples changed from being nominally temperature independent, characteristic of a heavily doped semiconductor, to an exponential temperature dependence expected for a semiconductor, with band gaps of ∼0.1 eV. Seebeck measurements confirm the reduction in electrically active defect concentration with increasing annealing temperature. The nonequilibrium defect concentration trapped by low-temperature crystallization and varying composition, combined with the annealing studies, allowed a wide range of structural and electrical properties to manifest within a limited sample set.

Lattice dynamics in the FeSb3skutterudite

“…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.…”

Structural and thermoelectric properties ofFeSb3skutterudite thin films

“…This effect becomes stronger for Sb rich samples and can be attributed mainly to better crystallinity by less Sb interstitials and Sb evaporation resulting in a relaxation towards the smaller equilibrium lattice constant of stoichiometic FeSb 3 films as also observed for Sb rich CoSb 3 films 8,31 . Thus this equilibrium lattice constant a (neglecting stress) can be determined from XRD measurements of single phase FeSb 3 films with (nearly) stoichiometric Sb content after annealing at 300 • C. Therefore a XRD (θ/2Θ) scan of an annealed FeSb 3 film with a Sb content of 76 at.% was analyzed by performing a Rietveld refinement shown in fig.…”

“…Details will be discussed in the following section. Please note that this value corresponds to slight n-type doping, which can be explained by the excess of Sb compared to stoichiometric films 31 . In fig.…”

Structural properties of thermoelectric CoSb3 skutterudite thin films prepared by molecular beam deposition

“…In literature several publications for skutterudite thin films prepared via sputtering [7,[14][15][16], pulsed laser deposition (PLD) [17][18][19][20] or modulated elemental reactant method (MERM) [21][22][23][24] can be found, but all of them describe films thicker than 70 nm, which is in a range, where the benefits due to nanosize effects are limited. Many difficulties are reported in these works for achieving single-phase films, especially for film deposition on heated substrates.…”