NMR study of the LiMnPO4·OH and MPO4·H2O (M=Mn, V) homeotypic phases and DFT calculations

Following our previous work on the tavorite-like LiFePO4·OH and FePO4·H2O phases, we report here the magnetic and NMR characterizations of analogous LiMnPO4·OH, MnPO4·H2O and VPO4·H2O phases together with the DFT calculations of the NMR shifts. The first two compounds exhibit Curie-Weiss type magnetic behavior with Curie constants close to the theoretical ones for HS Mn3+, while the vanadium compound is very close to a pure Curie-type behavior. 7Li, 31P and 1H MAS NMR spectra are reported for the three compounds, and show strong Fermi-contact shifts for the first two nuclei, while the sign and magnitude of the 1H shifts are very different for the three phases.DFT calculations (FLAPW in GGA+U approximation) using the WIEN2k code and the experimental susceptibilities are shown to reproduce closely the experimental data. This situation is compared to the case of the homologous and isostructural Fe compounds, which exhibit much more complex magnetic behaviors.