Formation of ε-Fe2O3 phase by the heat treatment of α-Fe2O3/SiO2 nanocomposite

Starting from a nanocomposite consisting of 4 nm hematite nanoparticles embedded in a silica matrix (30 wt.% hematite) and by applying heat treatments at increasing temperatures up to 1050 °C, gradual formation of ε-Fe2O3 phase was obtained. Besides representing a new synthesis route of ε-Fe2O3 phase, the results obtained in this work indicate that under certain conditions hematite nanoparticles are not thermally stable. Hence, like other ferric oxide polymorphs, nanosized hematite can undergo thermally triggered, size-induced structural phase transitions.