Mechanosynthesis and magnetic properties of LaFeO3

A.A. CRISTÓBAL; P.M. BOTTA; P.G. BERCOFF; ESTEBAN F. AGLIETTI; H.R. BERTORELLO; JOSÉ M. PORTO LÓPEZ

Buenos Aires

Simposio; XV International Symposium on Metastable, Amorphous and Nanostructured Materials (ISMANAM); 2008

UBA

Perovskite LaFeO3 and related compounds have attracted considerable attention due to their wide uses in fuel cells [1]. The structure and properties of these materials are strongly influenced by the synthesis processing of its precursor powders. For this reason the improvement of preparation conditions of these oxides has drawn much interest in the last years, leading to the use of several synthesis methods such as hydrothermal synthesis [2], combustion synthesis [3], sol–gel [4], etc. In this work LaFeO3 was synthesized by mechanochemical activation of Fe3O4 and La2O3  mixtures. The resulting powders were thermally treated at temperatures ranging from 600 to 1000ºC. All samples were analyzed by XRD, VSM and SEM. DRX reveals that the formation of LaFeO3 starts at only 60 min of milling. Longer times significantly increase the diffracted intensity of LaFeO3 peaks. After thermal treatments an increase in crystallinity was observed, which indicates that during the heating structural defects were healed, and crystallite sizes became larger. Magnetic hysteresis loops at room temperature (Fig. 1) show a decrease of the saturation magnetization (Ms) and coercivity (Hc) with activation time. This behavior confirms the gradual consumption of Fe3O4 together with the formation of antiferromagnetic LaFeO3, although there still remains a ferromagnetic contribution after an activation of 3h. M-H curves of activated and heated samples show an antiferromagnetic response, thus confirming the completion of the reaction. However, a very weak  ferromagnetic contribution is observed, essentially due to canting in the alignment of the two coupled sub-lattices in the LaFeO3 perovskite structure [5].       References: [1] N.Q. Mih, J. Am. Ceram. Soc. 76 (1993) 563. [2] W.J. Zheng, R.H. Liu, D.K. Peng, G.Y. Meng, Mater. Lett. 43 (2000) 19. [3] A. Chakraborty, P.S. Devi, H.S. Maiti, J. Mater. Res. 10 (1995) 918. [4] J. Xiao, G.Y. Hong, D.C. Yu, X.T. Dong, Acta Chim. Sin. 52 (1994) 784. [5] M. Rajendran, A.K. Bhattacharya,  J. Eur. Ceram. Soc. 26 (2006) 3675.