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New metastable olivine phases of sodium metal phosphates, NaMn1–xMxPO4 (M = Fe, Ca, Mg), nanorods are synthesized by a simple solid-state reaction at low temperature (≤100 °C) by means of a topotactic molten salt reaction that converts NH4Mn1–xMxPO4•H2O (M = Fe, Ca, Mg) to NaMn1–xMxPO4. Their crystal structures are characterized via XRD Rietveld refinement and electron diffraction. A full range of solid solution behavior was observed for olivine Na1–xMn0.5Fe0.5PO4, in contrast to that of LiMPO4 (M = Fe, Mn) olivine materials, and is ascribed to ion size effects. The solid solution behavior of NaMn0.5Fe0.5PO4 was confirmed by electrochemical characterization.
Lee et al. (Wed,) studied this question.