Abstract
α-MgAgSb is a very promising thermoelectric material with excellent thermoelectric properties between room temperature and 300 °C, a range where few other thermoelectric materials show good performance. Previous reports rely on a two-step ball-milling process and/or time-consuming annealing. Aiming for a faster and scalable fabrication route, herein, we investigated other potential synthesis routes and their impact on the thermoelectric properties of α-MgAgSb. We started from a gas-atomized MgAg precursor and employed ball-milling only in the final mixing step. Direct comparison of high energy ball-milling and planetary ball-milling revealed that high energy ball milling already induced formation of MgAgSb, while planetary ball milling did not. This had a strong impact on the microstructure and secondary phase fraction, resulting in superior performance of the high energy ball milling route with an attractive average thermoelectric figure of merit of 0.9. We also show that the formation of undesired secondary phases cannot be avoided by a modification of the sintering temperature after planetary ball milling, and discuss the influence of commonly observed secondary phases on the carrier mobility and on the thermoelectric properties of α-MgAgSb.
Highlights
IntroductionWith the worldwide demand for energy increasing and the environmental impact of electrical power production being considered more thoroughly, novel sources of energy are being investigated.A high portion of the primary energy consumed around the world is lost as waste heat, for example, in the cement industry (around 66%) [1] as well as in automotive applications [2]
With the worldwide demand for energy increasing and the environmental impact of electrical power production being considered more thoroughly, novel sources of energy are being investigated.A high portion of the primary energy consumed around the world is lost as waste heat, for example, in the cement industry [1] as well as in automotive applications [2]
The difference between the powders caused significant differences in sintered samples, as the sample synthesized by planetary ball milling (PBM) contained various impurities (Mg3 Sb2, MgAg, Sb, Ag3 Sb and Ag3 Mg) while the one using high energy ball milling (HEBM) was almost pure and contained only a small proportion of Mg3 Sb2
Summary
With the worldwide demand for energy increasing and the environmental impact of electrical power production being considered more thoroughly, novel sources of energy are being investigated.A high portion of the primary energy consumed around the world is lost as waste heat, for example, in the cement industry (around 66%) [1] as well as in automotive applications [2]. It is well known that thermoelectric materials have the ability to convert heat directly into electricity, which makes them good candidates to turn this waste heat into a new source of energy. Thermoelectric materials have applications in various areas, from automotive to aeronautics and space applications, are currently powering the Curiosity rover on Mars and are considered fornovel heat harvesting systems for lunar energy production [3]. The maximum efficiency of a thermoelectric material is characterized by its figure of merit, zT = σSκ T , in which σ is the electrical conductivity, S the Seebeck coefficient and κ the thermal. A satisfactory of power factor (PF = S2 σ) is obtained with both a high Seebeck coefficient and electrical conductivity. Some thermoelectric materials are already well-optimized and commercially available, such as telluride (Bi2 Te3 , Sb2 Te3 )-based solid solutions, which represent the best thermo electric materials in the near room temperature range [5]
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