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Phase pure samples of the half-Heusler material TiCoSb were synthesised and investigated. Multi-temperature synchrotron powder X-ray diffraction (PXRD) data measured between 90 and 1000 K in atmospheric air confirm the phase purity, but they also reveal a decomposition reaction starting at around 750 K. This affects the high temperature properties since TiCoSb is semiconducting, whereas CoSb is metallic. Between 90 K and 300 K the linear thermal expansion coefficient is estimated to be 10.5 × 10−6K−1, while it is 8.49 10−6K−1between 550 K and 1000 K. A fit of a Debye model to the Atomic Displacement Parameters obtained from Rietveld refinement of the PXRD data gives a Debye temperature of 395(4) K. The heat capacity was measured between 2 K and 300 K and a Debye temperature of 375(5) K was obtained from modelling of the data. Coming from low temperatures the electrical resistivity shows a metallic to semiconducting transition at 113 K. A relatively high Seebeck coefficient of ∼−250 μV K−1was found at 400 K, but the substantial thermal conductivity (∼10 W mK−1at 400 K) leads to a moderate thermoelectric figure of merit of 0.025 at 400 K. [ABSTRACT FROM AUTHOR]