Multinuclear NMR and DFT calculations on the LiFePO₄.OH and FePO₄.H₂O homeotypic phases

Aurore Castets (1) , Dany Carlier-Larregaray (1) , Yuesheng Zhang (2) , Florent Boucher (2) , Nicolas Marx (1) , Laurence Croguennec (1) , Michel Ménétrier (1)

1 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux
2 IMN - Institut des Matériaux Jean Rouxel

⁷Li, ³¹P, and ¹H MAS NMR spectra and magnetic properties are reported for LiFePO₄*OH and FePO₄*H₂O. The former shows no Curie-Weiss-type behavior up to room temperature, while the latter tends to such a behavior in a restricted temperature range. Calculation strategies are discussed for the NMR shifts that result from Fermi contact interaction with the high spin Fe³⁺ ions. Zero Kelvin electron spin densities obtained by averaging over the ion size using VASP (with PAW potentials) range with those obtained at the nucleus from WIEN2k, with the GGA and GGA+U methods. The latter values have been scaled with the temperature of the NMR measurement by using the experimental magnetic susceptibility, yielding calculated NMR shifts. The agreement is quite satisfactory, but very much dependent on the exchange correlation potential used for the calculation. Possible reasons for this are discussed, also considering the difference in magnetic behaviors.

Domaines: Matériaux

Aurore Castets, Dany Carlier-Larregaray, Yuesheng Zhang, Florent Boucher, Nicolas Marx, et al.. Multinuclear NMR and DFT calculations on the LiFePO₄.OH and FePO₄.H₂O homeotypic phases. Journal of Physical Chemistry C, 2011, 115 (32), pp.16234-16241. ⟨10.1021/jp204767c⟩. ⟨hal-00619811⟩