Thermoelectric properties and lattice dynamics of tetragonal topological semimetal Ba₃Si₄

We report the lattice dynamics and thermoelectric properties of topological semimetal Ba₃Si₄. 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 Ba₃Si₄ is the origin for the rather large thermopower. Ba₃Si₄ shows high potential for a thermoelectric material with a Seebeck coefficient as large as -120 μV K^-1 for 0.2 electrons/formula units through the substitution of Ba by appropriate cations, such as Y.