Realizing both n- and p-types of High Thermoelectric Performance in Fe1-xNixTiSb half-Heusler compounds

Attaining high thermoelectric performance in the same compounds with close composition is crucial for practical application. Hereby, Fe1-xNixTiSb samples are synthesized by arc melting, ball milling and hot pressing, which exhibit both n- and p-types conducting depending on Fe/Ni ratio. The long range disorder distribution of Fe/Ni, which is closely related to low lattice thermal conductivity, is elaborated by transmission electron microscopy. In addition, the optimum ball milling time, which varies with different compositions, is determined by transport coefficient analysis. Moreover, the thermoelectric transport properties of Fe1-xNixTiSb samples are investigated in detail and the results indicate that Fe/Ni substitution leads to the increase in density of states effective masses and reduction in lattice thermal conductivity. As a result, the dimensionless figure of merit of 0.48 is obtained for p-type Fe0.65Ni0.35TiSb and 0.40 for n-type Fe0.3Ni0.7TiSb at 923 K, which is comparable to CoTiSb but without expensive elements. Our results will motivate continues efforts in searching for new half-Heusler compounds having high thermoelectric performance in both n- and p-types with close compositions.