Investigation of phase transformations of iron nanoparticles during thermal annealing

Structural properties and phase composition of nanoparticles based on iron oxide were studied. Mossbauer spectroscopy, X-ray diffraction, and scanning electron microscopy were used for the analysis of phase transformations. According to XRD and Mossbauer spectroscopy data, an increase in the annealing temperature, as well as the subsequent phase transformations of magnetite into maghemite and then to hematite, indicate an improvement in the structure and a decrease in microdistortions in the lattice as a result of annealing defects and vacancies. According to Mossbauer spectroscopy data at temperatures above 400°C, the lines of characteristic FeO, which are characteristic for disordered iron oxide, are observed, which also confirms the improvement of the crystal structure of nanoparticles.