Enhanced thermoelectric performance in Ti(Fe, Co, Ni)Sb pseudo-ternary Half-Heusler alloys

TiFe_0.5Ni_0.5Sb-based half-Heusler compounds have the intrinsic low lattice thermal conductivity and the adjustable band structure. Inspired by the previously reports to achieve both p- and n-type components by tuning the ratio of Fe and Ni based on the same parent TiFe_0.5Ni_0.5Sb, we selected Co as the amphoteric dopants to prepare both n-type and p-type pseudo-ternary Ti(Fe, Co, Ni)Sb-based half-Heusler alloys. The carrier concentration, as well as the density of states effective mass was significantly increased by Co doping, contributing to the enhanced power factor of 1.80 mW m⁻¹ K⁻² for n-type TiFe_0.3Co_0.2Ni_0.5Sb and 2.21 mW m⁻¹ K⁻² for p-type TiFe_0.5Co_0.15Ni_0.35Sb at 973 K. Combined with the further decreased lattice thermal conductivity due to the strain field and mass fluctuation scattering induced by alloying Hf on the Ti site, peak ZTs of 0.65 in n-type Ti_0.8Hf_0.2Fe_0.3Co_0.2Ni_0.5Sb and 0.85 in p-type Ti_0.8Hf_0.2Fe_0.5Co_0.15Ni_0.35Sb were achieved at 973 K, which is of great significance for the thermoelectric power generation applications.