Distinct impact of order degree on thermoelectric power factor of p-type full-Heusler Mn₂VAl compounds

Full-Heusler compounds have three crystal structures with a different order degree; the highly ordered L2₁, partially disordered B2, and completely disordered A2 structures. To reveal the effects of the order degree on thermoelectric (TE) properties of the full-Heusler compounds, Mn₂VAl samples with varied L2₁ and B2 order degrees are prepared by changing preparation conditions, and their Seebeck coefficients and electrical conductivities are measured in a wide temperature range. As the B2 order degree becomes higher, the Seebeck coefficient increases, leading to the increase of the power factor (PF). The maximum PF is 2.84 10^-4 Wm^-1 K^-2 at 767 K for the Mn₂VAl sample with the highest B2 order degree. This study demonstrates that the TE properties of Mn₂VAl can be enhanced by increasing the fraction of the B2 phase. A relation between the Seebeck coefficient and crystal structures is also discussed based on the calculation of the electronic density of states of Mn₂VAl with the L2₁ and B2 structures.