Thermodynamic properties of TaCr ₂ and NbCr ₂

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The heat capacities of the Laves phases TaCr2 and NbCr2 have been measured between 10 and 350 K and the thermodynamic functions in this temperature range derived. The (heat capacity, temperature) curves have a simple sigmoid shape. The dissociation pressure of the NbCr2 phase at 1 472 K has also been determined experimentally. Combination of the present results with earlier experimental work on the heats and Gibbs energies of formation of TaCr2 shows that the entropy at 0 K is zero within the estimated experimental error of ±0.4 cal/g atom K. Published work on other Laves phases, such as CaMg2, and MgNi2 and KNa2, also show a very small “frozen-in” disorder at 0 K. The heats of formation of TaCr2 and NbCr2 at 298 K are –2.15 ± 0.2 and –1.67 ± 0.25 kcal/g atom, respectively. The entropies of formation are compared with other properties of Laves phases.