Formation and properties of BaxFe3-xO4 with spinel structure by mechanochemical reaction of α-Fe2O3 and BaCO3

Magnetic BaxFe3-xO4 (x similar to 0.23) with spinel structure was fabricated by ball milling of mixture of BaCO3 and nonmagnetic alpha-Fe2O3 powders, and the molar ratio of BaCO3 and alpha-Fe2O3 is 1:6. In the milling process, a mechanochemical reaction took place between BaCO3 and alpha-Fe2O3 and Ba cation incorporated into alpha-Fe2O3 with rhombohedral structure to form a alpha-(Fe,Ba)(2)O-3 solid solution. The Ba content in the alpha-(Fe,Ba)(2)O-3 increased with increasing milling time, when the Ba content exceeded a limited solubility, the alpha-(Fe,Ba)(2)O-3 transformed into a phase of BaxFe3-xO4 with spinel structure, where the Ba cation occupied an octahedral site or tetrahedral site. The product obtained in the balling process was different from that prepared in the annealing process at atmospheric pressure, which was BaFe2O4 with orthorhombic structure. Accompanying the crystal structure transition from alpha-(Fe,Ba)(2)O-3 to BaxFe3-xO4, the magnetic properties also changed from nonmagnetism into ferromagnetism. The saturation magnetization was 53.3 emu/g and coercivity was 113.7 Oe. The mechanism of transitions of the crystal structure was discussed in the present work. (C) 2009 Elsevier B.V. All rights reserved.