Effects of Crystalline Phase and Particle Size on the Properties of Plate-Like Fe2O3 Nanoparticles during γ- to α-Phase Transformation

Plate-like Fe2O3 nanoparticles were prepared in microporous regenerated cellulose films and then completely removed from the cellulose matrix by calcination. Crystallite size and properties variations of the nanosized Fe2O3 during gamma- to alpha-phase transformation were investigated. The gamma-Fe2O3 nanoparticles with an initial particle size of 24 nm increased from 26 to 83 nm with an increase of the calcination temperature from 350 to 800 degrees C, and the phase transformation temperature was about 500 degrees C. The nanoparticles made at 350 and 450 degrees C exhibited superparamagnetic properties with the corresponding blocking temperature (T-B) of about 83 and 80 K. The nanoparticles made at 500, 600, and 700 degrees C not only exhibited Curie transitions with T-B's of about 77, 54, and 15 K but also had Morin transitions from a pure antiferromagnet to a ferromagnet occurring at about 238, 240, and 246 K, respectively. However, the nanoparticles made at 800 degrees C only gave a clear Morin transition from a pure antiferromagnet to a ferromagnet at about 250 K. Furthermore, the nanoparticles also displayed different electrochemical properties.