Theoretical Study of Thermal Stability Impact of Alloying in α″–Fe₁₆N₂

α″–Fe₁₆N₂ has been investigated as one of promising candidates for environment-friendly magnets. While giant saturation magnetization has previously been experimentally observed in Fe₁₆N₂, its magnetic anisotropy and structural stability leave room for improvement. Recent theoretical studies have considered alloying Fe₁₆N₂ with various elements, including Cu and V, to improve the magnetic properties and/or stability against decomposition. However, estimates of stability in particular are typically restricted to simple ground-state-energy comparisons, effectively taken at 0 K. For a more practical measure of the effect of alloying on thermal stability of Fe₁₆N₂, we therefore extend ground-state energies, obtained with the plane-wave density-functional theory (DFT) code Quantum ESPRESSO, with appropriate empirical and/or statistical corrections to obtain free energies at arbitrary temperature. We then compare the temperature range of stability of ordered Fe_16-xV_xN₂ against the neighboring phases in the Fe-V-N ternary system, to estimate the range of temperatures at which it is stable, and compare against pure Fe₁₆N₂ to measure the effect of alloying on stability.