Nano-sized impurity phases in relation to the mode of preparation of LiFePO4

Microcrystalline LiFePO4 samples have been grown using four different techniques. The structural properties are analyzed using X-ray diffraction (XRD) spectroscopy and Fourier transform infrared spectroscopy (FTIR). Depending on which technique of preparation is used, the material is obtained either free of any detectable impurity, or include impurity phases under the form of nano-sized clusters. The magnetic properties are found to be a powerful tool to characterize them. They give evidence of nano-sized ferromagnetic particles, which can be either strongly magnetic (gamma-Fe2O3 clusters) or weakly ferromagnetic (Fe2P clusters), depending on the preparation process. The concentration of magnetic clusters also depends on the preparation process and varies from small concentration (1.0 x 10(-6) of gamma-Fe2O3 per formula) in which case no collective behavior is observed, to large concentrations (1.9 x 10(-4) of Fe2P clusters per formula) where the dipolar interaction generates superferromagnetism. Ferromagnetic resonance experiments are also reported, and are a probe of the gamma-Fe2O3 nanoparticles. An overall understanding of the different properties is achieved within a model of superferromagnetism induced by interacting Fe,P nanoparticles, which is also reported. (c) 2006 Elsevier B.V. All rights reserved.