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Materials Data on Ba(SbAu)2 by Materials Project

Ba(AuSb)2 crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. Ba2+ is bonded in a 1-coordinate geometry to eight Au1- and two equivalent Sb atoms. There are a spread of Ba–Au bond distances ranging from 3.45–4.01 Å. Both Ba–Sb bond lengths are 3.63 Å. There are two inequivalent Au1- sites. In the first Au1- site, Au1- is bonded in a 10-coordinate geometry to four equivalent Ba2+, two equivalent Au1-, and four equivalent Sb atoms. Both Au–Au bond lengths are 3.09 Å. There are one shorter (2.86 Å) and three longer (2.87 Å) Au–Sb bond lengths. In the second Au1- site, Au1- is bonded in a 9-coordinate geometry to four equivalent Ba2+ and five Sb atoms. There are a spread of Au–Sb bond distances ranging from 2.75–2.94 Å. There are two inequivalent Sb sites. In the first Sb site, Sb is bonded to four equivalent Au1- atoms to form a mixture of corner and edge-sharing SbAu4 tetrahedra. In the second Sb site, Sb is bonded in a 5-coordinate geometry to two equivalent Ba2+ and five Au1- atoms.

36 MATERIALS SCIENCE↗

High Thermoelectric Performance and Defect Energetics of Multipocketed Full Heusler Compounds

We report a first-principles density-functional study of electron-phonon interactions in and thermoelectric transport properties of the full Heusler compounds Sr 2 BiAu and Sr 2 SbAu. Our results show that ultrahigh intrinsic bulk thermoelectric performance across a wide range of temperatures is physically possible and point to the presence of multiply degenerate and highly dispersive carrier pockets as the key factor for achieving this. Sr 2 BiAu, which features ten energy-aligned low-effective-mass pockets (six along Γ-X and four at L), is predicted to deliver n-type zT=0.4-4.9 at T=100-700 K. Comparison with the previously investigated compound Ba 2 BiAu shows that the additional L pockets in Sr 2 BiAu significantly increase its low-temperature power factor to a maximum value of 12 mW m -1 K -2 near T=300 K. However, at high temperatures the power factor of Sr 2 BiAu drops below that of Ba 2 BiAu because the L states are heavier and subject to strong scattering by phonon deformation, as opposed to the lighter Γ-X states, which are limited by polar-optical scattering. Sr2SbAu is predicted to deliver a lower n-type zT=3.4 at T=750 K due to appreciable misalignment between the L and Γ-X carrier pockets, generally heavier scattering, and a slightly higher lattice thermal conductivity. Soft acoustic modes, which are responsible for the low lattice thermal conductivity, also increase the vibrational entropy and high-temperature stability of these Heusler compounds, suggesting that their experimental synthesis may be feasible. The dominant intrinsic defects are found to be Au vacancies, which drive the Fermi level towards the conduction band and work in favor of n-doping.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗