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

Plate-like Fe 2 O 3 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 Fe 2 O 3 during γ- to α-phase transformation were investigated. The γ-Fe 2 O 3 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 °C, and the phase transformation temperature was about 500 °C. The nanoparticles made at 350 and 450 °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 °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 °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.