Abstract
Enhancing the efficiency of thermoelectric materials has been practiced extensively by either improving the power factor or reducing the lattice thermal conductivity. Magnetism, and the magnetic moment–charged carrier interactions, has been suggested to enhance the efficiency of some compounds. Nevertheless, decoupling of the magnetic and the carrier concentration–related effects has never been achieved to prove once and for all, the importance of magnetism in thermoelectricity. Herein, we report improved quality criterion of bismuth telluride upon chromium substitution. The magnetic interactions with the magnetic moment carried by Cr atoms have increased the electrons' effective mass, enhancing the thermopower. Combined with the decrease in the lattice thermal conductivity, the overall performance of these compounds has been enhanced by 25% at constant carrier concentration, an improvement seldom observed. This is a robust enhancement principle because magnetic interactions are effective at high temperatures above the transition temperature, unlike magnon drag which is dependent on ordering and typically a low temperature phenomenon. Our results indicate that taking advantage of such relatively easily implemented magnetic doping effects along with existing strategies can lead to enhanced efficiency of thermoelectric materials.
Highlights
Solid-state thermoelectric generators have been increasingly attracting attention in the past decades owing to the need for new technologies for energy conversion [1e3]
The aim of this study was to decouple the effect of magnetism and the carrier concentrationerelated effect to prove the importance of magnetism on thermoelectricity; this was not viable to achieve in complex chemistries, and we demonstrated the magnetic enhancement effect in this way
We demonstrated the possibility of isovalent substitution of Cr for Bi, keeping the carrier concentration roughly constant up to x 1⁄4 0.01 and decoupling the carrier concentration and magnetic scattering effects on the thermopower
Summary
Solid-state thermoelectric generators have been increasingly attracting attention in the past decades owing to the need for new technologies for energy conversion [1e3]. Thermoelectric materials convert heat to electricity and vice versa, leading to new systems for waste heat recovery from automobiles and industries or power generations for sensors, and refrigeration. The efficiency of thermoelectric materials is defined by figure of merit, zT 1⁄4 S2 r:k T, where. Substantial efforts have been devoted to reduce the lattice thermal conductivity of bulk thermoelectric materials by seeking materials with intrinsically low thermal conductivity [4e7] or nanostructuring bulk materials [8e10]. Despite the popularity of bulk nanostructuring in the last decade, the reduction of the lattice thermal conductivity is achieved at the expense of reduced carrier mobility, initiated from scattering of charge carriers [11e13]. Improving the power factor, S2s, seems to be the most viable strategy to further enhance the efficiency of thermoelectric materials. There is a conventional trade-off between S and 1/r
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