Electronic structure and thermoelectric properties of full Heusler compounds Ca2YZ (Y = Au, Hg; Z = As, Sb, Bi, Sn and Pb)

Abstract

We investigate the transport properties of bulk Ca₂YZ (Y = Au, Hg; Z = As, Sb, Bi, Sn and Pb) by a combination method of first-principles and Boltzmann transport theory. The focus of this article is the systematic study of the thermoelectric properties under the effect of a spin–orbit coupling. The highest dimensionless figure of merit (ZT) of Ca₂AuAs at optimum carrier concentration are 1.23 at 700 K. Interestingly enough, for n-type Ca₂HgPb, the maximum ZT are close to each other from 500 K to 900 K and these values are close to 1, which suggests that semimetallic material can also be used as an excellent candidate for thermoelectric materials. From another viewpoint, at room temperature, the maximum PF for Ca₂YZ are greater than 3 mW m⁻¹ K⁻², which is very close to that of ∼3 mW m⁻¹ K⁻² for Bi₂Te₃ and ∼4 mW m⁻¹ K⁻² for Fe₂VAl. However, the room temperature theoretical κ_l of Ca₂YZ is only about 0.85–1.6 W m⁻¹ K⁻¹, which is comparing to 1.4 W m⁻¹ K⁻¹ for Bi₂Te₃ and remarkably lower than 28 W m⁻¹ K⁻¹ for Fe₂VAl at same temperature. So Ca₂YZ should be a new type of promising thermoelectric material at room temperature.