Abstract
Thermoelectric materials are outstanding to transform temperature differences directly and reversibly into electrical voltage. Exploiting waste heat recovery as a source of power generation could help towards energy sustainability. Recently, the SnSe semiconductor was identified, in single-crystal form, as a mid-temperature thermoelectric material with record high figure of merit, high power factor and surprisingly low thermal conductivity. We describe the preparation of polycrystals of alloys of SnSe obtained by arc-melting; a rapid synthesis that results in strongly nanostructured samples with low thermal conductivity, advantageous for thermoelectricity, approaching the amorphous limit, around 0.3–0.5 W/mK. An initial screening of novel samples Sn1−xMxSe, by alloying with 3d and 4d transition metals such as M = Mn, Y, Ag, Mo, Cd or Au, provides for a means to optimize the power factor. M=Mo, Ag, with excellent values, are described in detail with characterization by x-ray powder diffraction (XRD), scanning electron microscopy (SEM), and electronic and thermal transport measurements. Rietveld analysis of XRD data demonstrates near-perfect stoichiometries of the above-mentioned alloys. SEM analysis shows stacking of nanosized sheets, with large surfaces parallel to layered slabs. An apparatus was developed for the simultaneous measurement of the Seebeck coefficient and electric conductivity at elevated temperatures.
Highlights
Thermoelectric materials hold a tantalizing promise of greater energy efficiency by providing a robust and clean option for waste heat recovery and conversion to useful electrical energy through the Seebeck effect [1–5]
While σ is directly proportional to the carrier concentration n, the Seebeck coefficient is inversely proportional to it (n−2/3), a common rule for doped semiconductors known since the 1950s as the Pisarenko relation, after Mr N
About 2 g ingots were obtained in each case; a part was ground to powder for structural characterization, the remaining pellet was used for transport measurements
Summary
Thermoelectric materials hold a tantalizing promise of greater energy efficiency by providing a robust and clean option for waste heat recovery and conversion to useful electrical energy through the Seebeck effect [1–5]. This is related to the inherent difficulty to obtain, at the same time, a high electrical conductivity, a low thermal one, and a very high Seebeck voltage. Thermoelectric materials are characterized, for research purposes, by the thermoelectric figure of merit, zT = _σ_κ S_2 T, combining into a dimensionless number the Seebeck coefficient, S (the larger, the better), the electrical conductivity, σ (the larger, the better, to minimize waste through Joule-heating), the thermal conductivity, κ (the smaller, the better, to minimize thermally shorting the temperature gradient giving the Seebeck voltage), and the absolute temperature, T.
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