Thermoelectric Properties of Heusler Fe2TiSn Alloys

It is commonly believed that reducing the thermal conductivity of Heusler alloys is important for improving their thermoelectric properties. In this study, we focused on Fe2TiSn, which exhibits a relatively low thermal conductivity among Heusler alloys, to investigate the advantages of a powder metallurgy method that can easily form samples of desired shapes and produce dense samples with less segregation. We prepared sintered Fe2TiSn specimens using powders milled in air or Ar for 1 h, 3 h, and 12 h. We found that varying the non-stoichiometric composition led to deviations from the Fe2TiSn content of samples milled in air as a result of the appearance of a second phase, and the temperature at which the Seebeck coefficient changes from p-type to n-type decreased with increasing milling time for samples milled in air. For samples milled in Ar, no change in the Seebeck coefficient with milling time was observed. Although no significant difference was found between the electrical resistivities and thermal conductivities of samples milled in air and Ar, increasing the milling time promoted phonon scattering at the grain boundaries and reduced the lattice thermal conductivity. We determined a maximum dimensionless figure-of-merit of 0.0014 at 285 K for the Fe2TiSn alloy milled in Ar for 3 h.