Mössbauer studies of ɛ-Fe_3−x Ni _x N and γ′-Fe_4−y Ni _y N nanoparticles

Abstract

Nanocrystalline ɛ-Fe_3−x Ni _x N (0.0 ≤ × ≤ 0.8) particles are synthesized by precursor technique and nitridation of decomposed products in NH₃ (g) in the temperature range 673 K-823 K. For x = 0.1–0.4 compositions, single phase ɛ-Fe_3−x Ni _x N hexagonal structure with space group P6₃/mmc is formed, while for x = 0.5–0.8, fcc γ′-Fe_4−y Ni _y N phase is also precipitated. The room temperature Mössbauer spectrum for all the compositions shows the presence of superparamagnetic doublet, which is attributed to ɛ-Fe_3−x Ni _x N phase. For x = 0.5–0.8 compositions, two additional sextets are observed corresponding to two different iron sites, the corner position (Fe^c) and the fcc position (Fe^f), in γ′-Fe_4−y Ni _y N. The added Ni atoms preferentially substitute the corner Fe^c positions. The isomer shift, quadrupole splitting and hyperfine field values are found to change with the Ni content.