Mobility of nitrogen in ε-Fe3N below 150 °C: The activation energy for reordering

Previously quenched (from 573 K) ε-iron nitride powder of a composition close to Fe3N, which shows partial disorder in the interstitial N superstructure, can be reordered by annealing between 373 and 408 K. The kinetics of the reordering can experimentally be traced by the axial ratio (chcp/ahcp), as measured by X-ray powder diffraction, and can be described by a first-order rate law for the time-dependence of (chcp/ahcp) with an Arrhenius-type temperature dependence of the rate constant. The determined activation energy of 144 ± 5 kJ mol−1 can be associated with specific jumps of N atoms from disorder to order sites. The order-of-magnitude of the pre-exponential factor of (7 ± 10) × 1013 s−1 can be related with the vibration frequency of the N atom in an octahedral site.