Theoretical and experimental investigations of the structural, magnetic, electronic, and electrical properties of olivine LiFePO4

Abstract

The LiFePO4 and FePO4 compounds were synthesized by coprecipitation method. The X-ray diffraction and magnetic measurements were used to determine the crystal structure and to investigate the magnetic properties, respectively. From theoretical investigation point of view, self-consistent ab initio calculations, based on Density Functional Theory approach and using Full Potential linearized Augmented Plane Wave (FLAPW) method, were performed to investigate both electronic and magnetic properties of the LiFePO4. Polarized spin and spin–orbit coupling are included in calculations within the framework of the antiferromagnetic state between two adjacent Fe plans. Magnetic moments considered to lie along (010) axes are computed. In addition, average equilibrium voltage over a full cycle (Vcell) of the LiFePO4 battery is estimated from our FLAPW calculations. Computed magnetic moments are used as input for the high temperature series expansion (HTSE) calculations to compute other magnetic parameters. The exchange interactions between the magnetic atoms Fe–Fe and Fe–O–Fe in LiFePO4 are obtained using the mean field theory. The Néel temperature and critical exponent associated with the magnetic susceptibility are obtained employing HTSEs. The obtained inverse magnetic susceptibility is revealed in good accordance with our experimental data.