Optimized Synthesis of the Elusive ε-Fe₂O₃ Phase via Sol−Gel Chemistry

Abstract

ε-Fe 2 O 3 nanoparticles embedded in a SiO 2 matrix have been synthesized by sol−gel chemistry and high temperature heat treatments. Virtually pure ε-Fe 2 O 3 (in excess of 93%) is obtained, although a two-phase mixture, ε-Fe 2 O 3 + α-Fe 2 O 3, is observed for Fe 2 O 3 /SiO 2 ratios greater than 37 wt %. The ε-Fe 2 O 3 nanoparticles are stable up to ∼1600 K. Optimized ε-Fe 2 O 3 nanoparticles are ferrimagnetic, with a Curie temperature T C ≈ 510 K, and remarkably high values of room-temperature coercivity, H C = 20 kOe.