Synthesis, characterization and vibrational spectroscopic study of Co, Mg co-doped LiMnPO4

• Simple synthetic route for LiMn0.8Co0.1Mg0.1PO4
• Confirmation of the single phase of Co and Mg co-doped LiMnPO4
• Report the solid state reaction mechanism between the precursor and Li-source
• Report the IR spectra with respect to the vibrations of NH4+, PO43 ‐, P2O74 ‐, H2O
• Report on factor group analysis of the title compound and its precursor

The isostructural olivine-like LiM(II)PO4 compounds [M(II) = Mn, Mn0.9Co0.1, Mn0.8Co0.1Mg0.1] were successfully generated through the solid state reaction from the synthesized NH4M(II)PO4∙ H2O precursors. The TG/DTG/DTA, AAS/AES, FTIR and XRD methods were employed to confirm both NH4M(II)PO4∙ H2O and LiM(II)PO4 compounds. Their morphologies were studied by SEM method. The shift of two theta angle of XRD to higher values was observed in metal doping compounds, which indicate the formation of the single phase of isodivalent doping of Co2 + and Mg2 + ions according to the change in the lattice parameters and cell volumes. Their infrared spectra are reported and discussed with respect to the normal vibrations of NH4+, PO43 ‐, P2O74 ‐ and H2O molecules using factor group analysis. The correlation field splitting analysis of PO43 ‐ in NH4M(II)PO4∙ H2O (orthorhombic system, Pmn21, C2v7 and Z = 2, [(3 × 5) − 6] × 2 = 18 internal modes) symbolized as Td − Cs − C2v7 suggested the number of vibrational modes to be: ΓVib = A1(6) + A2(3) + B1(6) + B2(3) and A1(6) + A2(3) + B1(3) + B2(6) for zx and yz plane respectively. While, LiM(II)PO4 crystallizes in the orthorhombic system the space group Pnma (D2h16), Z = 4 and the site symmetry of PO43 ‐ is Cs. The correlation field splitting of type Td − Cs − D2h16 were reported in relation to [(3 × 5) − 6] × 4 = 36 internal modes for PO43 ‐ unit in the structure.

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