Thermodynamic stability of RNi2 Laves phases

• A home-made high-temperature calorimeter has been employed.
• The ΔfH° at 300 K for the RNi2 (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho and Er) phases has been obtained.
• A gradual decreasing trend of the ΔfH° with the increasing of the R atomic number has been found.

A calorimetric study of the RNi2 Laves phases (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho and Er) has been carried out to determine the heat of formation (ΔfH°) at 300 K using a high temperature direct drop calorimeter. The reliability of the calorimetric results has been determined and supported by using different analytical techniques: light optical microscopy, scanning electron microscopy equipped with electron probe microanalysis (EPMA) with energy dispersive X-ray spectroscopy (EDS) detector and X-ray powder diffraction analysis. We observed a gradual regular decreasing trend of the heat of formation with the increasing of the rare-earth atomic number from −34 ± 1.5 kJ/mol for PrNi2 to −50 ± 1 kJ/mol for ErNi2. Results have been discussed and compared with the data previously reported in the literature.

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