Electronic and Lattice Vibrational Properties of BaSi2 from Density Functional Theory Calculations

Abstract

BaSi 2 is a potential thermoelectric material because of its very low thermal conductivity. Using the full-potential linearized augmented plane-wave method and semiclassical Boltzmann theory, thermoelectric transport properties of BaSi 2 have been investigated. The calculations show that the thermoelectric properties can be remarkably improved by optimizing the carrier concentration. The linear response method within the framework of density functional theory was employed to investigate the underlying physics of heat transport. There are rather flat optical dispersion curves and low frequency of acoustic phonon modes in the phonon band structure of BaSi 2 . The low-lying optical phonon branch at the C point of the Brillouin zone (BZ) corresponds to rigid-unit vibration of the Si tetrahedron. The rigid-unit vibration mode confines the acoustic phonon modes and scatters the heat-carrying acoustic modes, leading to the low lattice thermal conductivity.

Polarized Raman spectra of BaSi2epitaxial film grown by molecular beam epitaxy

“…21,22,27) In the first-principles calculations of the partial phonon density of states (DOS) for BaSi 2 , only the Si-related phonon modes locate at high wavenumbers of 280-500 cm −1 . 28,29) These vibrational properties observed in BaSi 2 convince us that the Raman lines at 280-500 cm −1 are the internal modes of the isolated Si cluster in BaSi 2 . According to the factor group analysis using the T d symmetry, the Raman tensors are given by 20) A 1 where a, b, and d are components of the Raman tensors.…”

“…In the result of the partial phonon DOS, the Ba-related phonon modes locate at wavenumbers lower than 100 cm −1 . 28,29) Therefore, the five Raman lines observed at 90-150 cm −1 are assigned to the external modes of the isolated Si cluster in BaSi 2 . The type of the external modes such as rotation and translation is unclear, 32) but the θdependences of Raman intensities were classified into two types.…”

Recent advances in computational studies of thin-film solar cell material BaSi2

“…Figure 8 the phonon band structure (calculated from firstprinciples) along high-symmetry points in the Brillouin zone and the partial phonon DOS for BaSi 2 . 64) There is no branch with negative frequency, confirming that this crystal structure is stable. BaSi 2 has optical phonons with low-frequency which interact with acoustic phonons.…”

Phonon transport properties of NbCoSb compound

“…This interaction increases the likelihood of scattering of the acoustic modes by the optical modes. So, the lattice thermal conductivity could also suppress [22,23]. Also, some optical modes are nearly flat, and these optical modes contribute little toward heat transport [24,25].…”