Structure and electrochemical study of Li2xMn(1-x)TiCr(PO4)3 (x = 0-0.50) with Nasicon-like structure

The crystal structures of MnTiCr(PO4)(3) and LiMn0.50TiCr(PO4)(3) were determined at room temperature from X-ray powder diffraction using Rietveld analysis. The two materials exhibit the Nasicon-type structure, (S.G.:R(3) over barc$). The structure of MnTiCr(PO4)(3) is similar to that of NaZr2(PO4)(3) with the Mn cations in the Na (Mi) sites. The Ti4+ and Cr3+ ions are statistically distributed in the octahedral Zr sites. The Mn atoms in LiMn0.50TiCr(PO4)(3) are statistically distributed in half of the M1 sites. From the X-ray data, it is difficult to unambiguously localize the lithium atoms. A comparative lithium intercalation study in LiMn0.50TiCr(PO4)(3), LiTi2(PO4)(3) and Mn0.50Ti2(PO4)(3) clearly shows that only the MZ sites are available for intercalation in the LiMn0.50TiCr(PO4)(3) phase. Therefore, we can assume that in the starring material, the M1 sites are fully occupied leading to the cationic distribution [Li0.50Mn0.50](M1)[Li-0.50](M2)TiCr(PO4)(3).