Enhancement of the thermoelectric performance of b-Zn 4 Sb 3 by in situ nanostructures and minute Cd-doping (original) (raw)
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Synthesis, Structures and Properties of Thermoelectric Materials in the Zn-Sb-In System
The challenging search for clean, reliable and environmentally friendly energy sources has fueled increased research in thermoelectric materials, which are capable of recovering waste heat. Among the state-of-the-art thermoelectric materials b-Zn 4 Sb 3 is outstanding because of its ultra-low glass-like thermal conductivity. Attempts to explore ternary phases in the Zn-Sb-In system resulted in the discovery of the new intermetallic compounds, stable Zn 5 Sb 4 In 2-δ (δ=0.15) and metastable Zn 9 Sb 6 In 2. Millimeter-sized crystals were grown from molten metal fluxes, where indium metal was employed as a reactive flux medium. Zn 5 Sb 4 In 2-δ and Zn 9 Sb 6 In 2 crystallize in new structure types featuring complex framework and the presence of structural disorder (defects and split atomic positions). The structure and phase relations between ternary Zn 5 Sb 4 In 2-δ, Zn 9 Sb 6 In 2 and binary Zn 4 Sb 3 are discussed. To establish and understand structureproperty relationships, thermoelectric properties measurements were carried out. The measurements suggested that Zn 5 Sb 4 In 2-δ and Zn 9 Sb 6 In 2 are narrow band gap semiconductors, similar to b-Zn 4 Sb 3. Also, the peculiar low thermal conductivity of Zn 4 Sb 3 (1 W/mK) is preserved. In the investigated temperature range 10 to 350 K Zn 5 Sb 4 In 2-δ displays higher thermoelectric figure of merits than Zn 4 Sb 3 , indicating a potential significance in thermoelectric applications. Finally, the glass-like thermal conductivities of binary and ternary antimonides with complex structures are compared and the mechanism behind their low thermal conductivities is briefly discussed.
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Using infrared reflection spectroscopy the authors show that the phase transitions from disordered high temperature -Zn 4 Sb 3 into the increasingly higher ordered and complex structured low-temperature phases ␣ and ␣Ј are accompanied by a significant increase in the free charge carrier density and a concomitant increase of the effective scattering rate.
Sb3Zn4, a promising new thermoelectric material. Elaboration and caracterisation
MRS Proceedings, 2001
Sb-Zn alloys have interesting thermoelectric properties. Sb3Zn4 is a high performance ptype thermoelectric material appearing as a promising substitute for PbTe due to a higher factor of merit, ZT=1.3 at 673K [1] with the advantage of being Pb free. The preparation of the Sb3Zn4 compound is, however, not without problems. Even if some authors reported measurements on a single-phased material or single crystals [1,2], others described it as multi-phased alloy giving confused explanations for this result based on the existence of metastabilities due to strong interactions in the liquid phase [3,4].Hence, the knowledge of a very trustful phase diagram of the Sb-Zn sytem is indispensable. As the previous published data on this system were discordant, we have reinvestigated it and from our results we have elaborated and characterised the thermoelectric compound Sb3Zn4.
Thermoelectric properties of Zn4Sb3 intermetallic compound doped with Aluminum and Silver
The b-phase Zn 4 Sb 3 has attracted much attention because of its high thermoelectric performance in the intermediate temperature range thanks to disorder in the Zn lattice site. In this work are presented structural, thermal, electric and thermoelectric characterization of Zn 4 Sb 3 pure and Ag, Al doped, prepared by a simple synthesis. Structural and microstructural analyses reveal homogeneous one-phases having compositions in agreement with the nominal ones. After thermoelectric characterization, Ag doping results mostly effective in lowering the resistivity and Seebeck coefficient value, by introducing holes in the system. On the other hand, the Al substitution yields a very small decrease of the Seebeck coefficient but, at the same time, a significant decrease of the thermal conductivity mainly due to the depressed phonon contribution. The thermal conductivity behavior is the main responsible for the good thermoelectric performances of (Zn 0.99 Al 0.01 ) 4 Sb 3 , whose thermoelectric figure of merit reaches the encouraging value of 0.23 at 260 K.
Nanovoids in thermoelectric β-Zn 4Sb 3: A possibility for nanoengineering via Zn diffusion
Acta Materialia, 2011
The binary Zn 4 Sb 3 phase is a promising material for thermoelectric applications due to its extraordinarily low thermal conductivity. The present study attempts to rationalize this property by investigating its nanostructure. b-Zn 4 Sb 3 samples with varying Zn content were thus synthesized, quenched from the melt and annealed at 350°C. Their nanostructure was observed using transmission electron microscopy. The samples presented in this work have Zn:Sb atomic ratios of 1.30 and 1.33 and exhibit a single phase of b-Zn 4 Sb 3 in X-ray diffraction studies. Transmission electron microscopy (TEM) observations revealed nanoporous morphologies for both compositions, with a random distribution of the voids. Both samples contain voids, while the sample with Zn:Sb = 1.33 also consists of Zn nanoinclusions. Density functional theory calculations were carried out to study the stability of atomistic b-Zn 4 Sb 3 models with varying Zn content. This was used to suggest a mechanism for the formation of Zn nanoparticles and subsequently nanovoids. The calculations imply that the Zn solubility in the Zn 4 Sb 3 matrix increases with decreasing temperature. Combined with a high Zn diffusivity, this work explains how Zn could leave the nanoprecipitates during annealing, resulting in the voids seen by TEM.
Advanced Electronic Materials
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