Ytterbium Silicide (YbSi 2 ): A Promising Thermoelectric Material with a High Power Factor at Room Temperature (Phys. Status Solidi RRL 2/2018)

The so‐called power factor S 2 σ (with S the Seebeck coefcient and σ the electrical conductivity) determines the power generation performance of thermoelectric (TE) devices. Since S and σ have a trade‐off relationship as a function of carrier concentration, it has been difficult to enhance S 2 σ . Metal silicide‐based TE materials have attracted attention in the past two decades, because they are less toxic than conventional TE materials (such as Bi 2 Te 3 and PbTe), involve low production cost and show high chemical stability. The study by Ken Kurosaki and co‐workers (see article no. 1700372 ) reveals that YbSi 2 can be a good candidate of TE materials working near room temperature: Metallic YbSi 2 has a specific layered structure and mixed valence state of Yb 2+ and Yb 3+ , where Yb 2+ is the major ionic component at low temperature, and the amount of Yb 3+ increases with increasing temperature. This temperature‐dependent valence fluctuation would increase S with keeping high σ , which enables to enhance the power factor of YbSi 2 to 2.2 mW m −1 K −2 which is comparable to that of Bi 2 Te 3 in the wide temperature range from room temperature to 523 K.