Thermoelectric properties and lattice dynamics of tetragonal topological semimetal Ba 3 Si 4 .

We report the lattice dynamics and thermoelectric properties of topological semimetal BaSi. The lattice dynamics has been studied by Raman and inelastic neutron scattering experiments. Good agreement has been found with first-principles calculations. The presence of low-energy optical modes at about 7 meV mainly due to the heavy mass of the Ba atoms suggests a propensity to low thermal conductivity, which is favorable for thermoelectric applications. Our density functional theory calculations indicate that the semimetallic nature of BaSi is the origin for the rather large thermopower. BaSi shows high potential for a thermoelectric material with a Seebeck coefficient as large as -120 μV K for 0.2 electrons/formula units through the substitution of Ba by appropriate cations, such as Y.