Improved lithium-ion transport in NASICON-type lithium titanium phosphate by calcium and iron doping.

Li1.2+xTi1.9−xFexCa0.1(PO4)3 (x=0.1–0.4) compounds were synthesized by a sol–gel method and studied by X-ray diffraction, SEM and 57Fe Mössbauer spectroscopy. The rhombohedral (R c) phase prevailed for all studied samples, while for x≥0.3 an orthorhombic Pbca phase appeared. The substitution of Ti4+ by Fe3+ and Ca2+ led to an increase of the unit cell parameters of the rhombohedral phase. The hyperfine 57Fe Mössbauer parameters showed a single signal ascribable to Fe3+ in an anisotropic distribution of charges surrounding the probe atom. The double substitution of Ti4+ by Fe3+ and Ca2+ in Li1.2+xTi1.9−xFexCa0.1(PO4)3 resulted in a net improvement of the ionic conductivity, as compared to pristine LiTi2(PO4)3. Ionic conductivities of 3.3·10−4 Scm−1 and 2.4·10−5 Scm−1 at room temperature, and 5.23·10−4 Scm−1 and 8.44·10−5 Scm−1 at 373K were observed for Li1.3Ti1.8Fe0.1Ca0.1(PO4)3 and Li1.6Ti1.5Fe0.4Ca0.1(PO4)3, respectively. [ABSTRACT FROM AUTHOR]