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Abstract:
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 x
10(-6) K(-1), while it is 8.49 10(-6) K(-1) between 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 mu VK(-1) was found at 400 K, but the substantial
thermal conductivity (similar to 10 W mK(-1) at 400 K) leads to a
moderate thermoelectric figure of merit of 0.025 at 400 K.
