Thrmoelectric properties of several p- and n-type half-Heusler compounds and effects of dopants

Half-Heusler compounds are attractive candidate of Phonon Glass Electron Crystal thermoelectric materials applicable at high temperatures. They exhibit semiconducting properties at Valence Electron Count (VEC) of nearly 18. In the present work, we categorized all half-Heusler compounds available in the literature by VEC, and selected several candidates by preliminary experiments. N-type HfNiSn and p-type TiFeSb are interesting because of their low thermal conductivity. Additionally, HfNiSn shows excellent Seebeck coefficient, and TiFeSb shows p-type property as a rare case in half-Heusler compounds. We have conducted our material design to effectively improve the thermoelectric figure of merit; to reduce lattice thermal conductivity by substituting heavier elements for constitutional elements and to enhance the power factor by doping impurities. Sample preparation was conducted using powder metallurgy in order to further reduce thermal conductivity. Thermoelectric properties were evaluated by measuring Seebeck coefficient, electrical resistivity and thermal conductivity at temperatures ranging from 300 to 1000 K.