Thermodynamic properties of TaCr2 and NbCr2

Abstract

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.