Transport and thermoelectric properties of Nb-doped FeV0.64Hf0.16Ti0.2Sb half-Heusler alloys synthesized by two ball milling regimes

This work presents experimental investigations of the thermoelectric properties of p-type FeV0.64−xNbxHf0.16Ti0.2Sb half-Heusler alloys. Samples of the concerned system were prepared through sequent procedures starting with arc melting. Fine powders of the concerned samples were then obtained by mechanical alloying using two different ball milling regimes. Spark plasma sintering technique was employed for pressing the powders. The thermoelectric properties were studied as functions of temperature from 300 K to 800 K. Alloy scattering of phonons showed great contribution in the reduction of lattice thermal conductivity. High energy ball milled FeV0.39Nb0.25Hf0.16Ti0.2Sb sample possessed the lowest lattice thermal conductivity with a value of 1.81 Wm−1 K−1 at room temperature with a reduction of –82% compared with that of FeVSb. Additionally, the electrical conductivity was improved by the Nb doping leading to notable increase in the material’s power factor. As a result, a maximum power factor of 19.5 μW cm−1 K−2 was achieved at 800 K for Nb doped at x = 0.4 of the ball milled samples. The figure of merit was increased from 0.25 for FeV0.64Hf0.16Ti0.2Sb to 0.44 for FeV0.60Nb0.4Hf0.16Ti0.2Sb due to Nb doping. Which means that the figure of merit value is enhanced by –43%. The value was recorded at 725 K.