Isovalent substitution effects on thermoelectric transport properties of CoSbX (X  =  S, Se, Te) system

Abstract

We demonstrate a transition of the thermoelectric transport characteristics in the CoSbX (X = S, Se or Te) systems from a p -type semiconductor to metallic conductor with increasing size of the X constituent. From DFT calculations CoSbS is found as an indirect semiconductor with band-gap of 0.38 eV, while both CoSbSe and CoSbTe appear as metals. For the two metals, the calculations reveal two degenerate electron pockets (located near the U point for CoSbSe and near the T point for CoSbTe) and a hole pocket along the X-Γ-Y points. In line with the theoretical predictions, electrical transport measurements reveal semiconductingtype temperature dependence of resistivity and positive room-temperature Seebeck coefficient (+570 µV K −1 ) for CoSbS, and metallic-type temperature dependence for CoSbSe and CoSbTe with negative Seebeck coefficient (−14 and −7.5 µV K −1 ). The Hall coefficient is positive for CoSbS(Se) and negative for CoSbTe. Room-temperature charge carrier densities were estimated at 3 × 10 18 /~10 21 /~10 22 cm −3 for CoSbS/CoSbSe/CoSbTe. Thermal conductivity is dominated by lattice rather than electronic contribution, the RT value being of the roughly same magnitude for all the three compounds. The temperature dependence of thermal conductivity bear resemblance to a typical semiconductor in the case of CoSbS and to a metallic alloy for CoSbSe and CoSbTe.

Unusual thermoelectric properties mediated by solute segregation in tellurium alloyed CoSbS

“…Previous density functional theory (DFT) calculations revealed that CoSbTe crystallizes in the Pnn 2 space group and exhibits a semimetal band structure. 55 Therefore, Te alloying in CoSbS would decrease the bandgap accordingly (Fig. 1a).…”

Tailor-made enzyme consortium segregating sclerenchyma fibre bundles from willow bark

“…Fibre bundle samples were characterized for the phase purity and crystal structure by X-ray diffraction (XRD; PANalytical X'Pert PRO MPD Alpha-1; Cu Kα1 radiation). 39 The relative crystallinity index was computed using an amorphous fitting method 40 applied to the scattering angle range of 13–50°. The crystalline part of the fibre bundle is modelled by using 20 Gaussian functions in the positions defined by the cellulose I beta crystal reflections (these gaussian peaks can be seen in Fig.…”

Interplay between positive magnetoresistance and thermoelectric properties by tuning carrier concentration in Sb2−x Sn x Te3 (x ⩽ 0.05) crystals

“…Topological insulators are recognized as the promising thermoelectric materials, where the tuning of carrier concentration and the intricate phonon scattering are proposed through the intrinsic or artificial manipulations. For example, the increase in the density of states, creating the defects and the interfaces have been manipulated for improving the thermoelectric properties [14][15][16][17][18][19][20][21][22]. Recently, the binary Sb 2 Te 3 has attracted special attention, when it has been identified as a three-dimensional (3D) topological insulator [23,24].…”