Screening more than 1,500 silicides to determine their thermoelectric properties

Thermoelectric (TE) devices hold promise in applications ranging from highly efficient refrigerators and generators to high-temperature waste heat harvesters. However, the technology is being held back partially due to the usage of toxic and rare materials, which limits its practical application.

Silicides, a group of silicon-based materials that is nontoxic and abundant, may help solve the problem. Løvvik et al. screened more than 1,500 silicides with an emphasis on doping for high-charge carrier concentration and alloying to achieve adequately low phonon thermal conductivity.

Using density functional theory (DFT) calculations based on an implementation of the Boltzmann transport theory, the authors developed an electronic transport model and incorporated scattering mechanisms relating to neutral impurities and electron-phonon interactions.

They identified three silicides with well-established TE properties for both p and n doping: manganese silicide (Mn₄Si₇), magnesium silicide (Mg₂Si) and silicon-germanium. They also identified a lithium magnesium silicon compound (Li₂MgSi), which has garnered interest for battery development but hasn’t been tested for TE properties, as being the most favorable for p-doping.

The predicted phonon thermal conductivity was low for all the compounds tested, indicating that phonon thermal conductivity may be less of a dominating factor than previously assumed.

The researchers hope their study would encourage experimental groups to investigate some of the promising compounds from their study that aren’t necessarily known for their TE properties.

“Many of the top candidates have never been tested for TE properties,” author Ole Martin Løvvik said.

Source: “Screening of thermoelectric silicides with atomistic transport calculations,” by Ole Martin Løvvik, Espen Flage-Larsen, and Gunstein Skomedal, Journal of Applied Physics (2020). The article can be accessed at https://doi.org/10.1063/5.0008198 .