Phase transformation from Fe4N to Fe3O4 due to electron irradiation in the transmission electron microscope

Abstract Fe4N crystals were exposed to intense electron beams at room temperature inside transmission electron microscopes (TEM) with base pressures of 10−5–10−6 Pa. The effects of irradiation on Fe4N along the [0 0 1], [0 1 1], [1 1 1] and [2 1 1] orientations were investigated in situ using selected area electron diffraction (SAED), high resolution electron microscopy (HREM), and electron energy loss spectroscopy (EELS). The dose rate of the electron beam for the irradiation experiments was in the range of 0.7–2×1024 e m−2 s−1. It was concluded that the initial Fe4N (γ′) transformed into Fe3O4 (O) with the cubic-to-cubic orientation relationship of (1 0 0) O //(1 0 0) γ ′ and [0 0 1] O //[0 0 1] γ ′ . This transformation is electron-irradiation dependent, which suggests a controlled method to prepare local Fe3O4 crystals (magnetite) in a Fe4N film using an electron beam.