We studied the phase stability in pseudobinary ${\left({\mathrm{Ni}}_{1-x}{\mathrm{Pt}}_x\right)}_3\mathrm{Al}$ alloys using a combination of first-principles calculations, a cluster expansion technique, and Monte Carlo simulations. Our ground state search yields $\mathrm{L}{1}_0$ ${\mathrm{Ni}}_2\mathrm{Pt}\mathrm{Al}$ and $\mathrm{L}{1}_0$ $\mathrm{Ni}{\mathrm{Pt}}_2\mathrm{Al}$ as the two stable ground state structures, and the latter has been observed experimentally. The calculated $c∕a$ ratio of $\mathrm{L}{1}_0$ $\mathrm{Ni}{\mathrm{Pt}}_2\mathrm{Al}$ is also in good agreement with experiments. By performing Monte Carlo simulations, the order-disorder transition temperatures of $\mathrm{L}{1}_0$ ${\mathrm{Ni}}_2\mathrm{Pt}\mathrm{Al}$ and $\mathrm{L}{1}_0$ $\mathrm{Ni}{\mathrm{Pt}}_2\mathrm{Al}$ were predicted to be $\sim 915\mathrm{K}$ and $\sim 1275\mathrm{K}$, respectively. The mixing enthalpies of random pseudobinary $\mathrm{L}{1}_2$ ${\left({\mathrm{Ni}}_{1-x}{\mathrm{Pt}}_x\right)}_3\mathrm{Al}$ alloys were also predicted using our cluster expansion, and the results agree well with direct first-principles calculations on Special Quasirandom Structures (SQS’s) for $\mathrm{L}{1}_2$ alloys developed in the present study.

• Received 16 August 2005

DOI:https://doi.org/10.1103/PhysRevB.72.184203