Phase transformations of Fe3N-Fe4N iron nitrides at pressures up to 30 GPa studied by in situ X-ray diffractometry

The parameters of the equation of state of the stable ɛ-Fe3N x (where x = 0.8) nitride in the Fe-N system have been determined at pressures up to 30 GPa and temperatures up to 1273 K. The parameters V 0 = 81.48(2) Å−3, K T = 162(3) GPa, K T = 4.0 = 1.66(2), γ0 = 555 K, and q = 1 have been determined for ɛ-Fe3N0.8 by the approximation of the P-V-T data with the Vinet equation of state and the thermal parameters within the Mie-Grüneisen-Debye formalism. No anomalous change in the volume of the cell owing to possible magnetic transitions has been revealed. The instability of Fe4N at high pressures and Fe3N in the presence of a deficit of nitrogen in the system has been established. The stable phase in the temperature range of 300–673 K and the pressure range of 20–30 GPa is ɛ-Fe3N rather than ɛ-Fe3N0.8.