High thermoelectric properties in full-Heusler X2YZ alloys (X = Ca, Sr, and Ba; Y = Au and Hg; Z = Sn, Pb, As, Sb, and Bi)

Abstract

The electronic and transport properties of a new class of full Heusler semiconductors X2YZ (X = Ca, Sr, and Ba; Y = Au and Hg; Z = As, Sb, Bi, Sn and Pb) are investigated using first-principles electronic structure methods and Boltzmann transport theory. The results show that the spin–orbit coupling not only affects the band-gap values but also the symmetry and dispersion of the top of the valence and bottom of the conduction band, so it should not be neglected in computation of electron transport properties. The electronegativity significantly affects the energy band gap and the strength of the Y-Z covalent bond, and thus affects the transport properties. By comparison the electronic transport properties of X2YZ with that of Fe2VAl and taking the lattice thermal conductivity into account, we predict the minimum value of the optimal figure of merit (ZT) should be more than 2.0 at 300 K. Interestingly, for the same carrier concentration, very similar p- and n-type thermoelectric performance is observed in both Ba2AuBi and Ba2AuSb, which is highly important for the fabrication of the thermoelectric modules with comparable efficiencies.