Enthalpies of formation of AlNi: Experiment versus theory

The thermodynamic properties of theB2 AlNi phase have been revisited with calorimetric and a priori theoretical estimates of the enthalpy of formation of the stoichiometric compound. The calorimetric study has surveyed the temperature dependence of the enthalpy of formation and extrapolated it to zero temperature (for which the a priori estimates have been made), while the theoretical estimate explores the consequences of an apparent error in local density-based potentials in yielding the magnetic contribution to the reference energy of Ni metal. The present experimental value, extrapolated to 0 K, is 65.915 kJ/g-atom while the local density-based calculated value is 67.5 kJ/g-atom. These are in accord with each other and with much, but not all, the previous experimental data. An estimate of the error in the local density magnetic energy was made by comparing experimental and calculated heats for nonmagnetic Fe compounds, where the energy and its associated error are much larger, and scaling the result to Ni. This yields a “corrected” theoretical heat of 66 kJ/g-atom.