Study of thermal stability of half-Heusler alloys TiFe1.33Sb and TixNb1-xFeSb (x = 0, 0.15) by differential thermal analysis and Knudsen effusion method

Half-Heusler alloys, a non-centrosymmetric structure variant of the Heusler type, create a category of advanced thermoelectric materials. The thermal and phase stability of half-Heusler alloys TiFe1.33Sb and TixNb1-xFeSb (x = 0, 0.15), prepared by various techniques (hot pressing, ball milling or high-energy ball milling and hot pressing, as well as in one case with additional annealing), have been studied by means of differential thermal analysis and the Knudsen effusion method. The results from the measurement of phase transformations and evaporation of antimony, as the volatile element, supported by microstructure measurements and by diffusion profiles are presented and discussed in view of the long-term operation stability of the thermoelectric materials investigated. The alloys TiFe1.33Sb and TixNb1-xFeSb have all evidenced only a slight evaporation of antimony and have proven their long-term stability at temperatures well above the operation temperature of ~873 K.