Lithium mobility in titanium based Nasicon Li1+xTi2−xAlx(PO4)3 and LiTi2−x Zrx(PO4)3 materials followed by NMR and impedance spectroscopy

Titanium-based Nasicon-type compounds with formula Li1+xTi2−xAlx(PO4)3 and LiTi2−xZrx(PO4)3, have been prepared and studied with X-ray Diffraction (XRD), Nuclear Magnetic Resonance (NMR) and Electric Impedance (EI) techniques. From the analysis of the 7Li and 31P NMR spectra, cation distribution and Li mobility have been deduced. The substitution of Ti4+ by a large Zr4+ cation expands the unit cell but the grain interior conductivity remains near that of the parent LiTi2(PO4)3 compound. However, substitution of Ti4+ by a smaller Al3+ cation reduces the unit cell dimensions of the Nasicon framework, but enhances about three orders of magnitude the conductivity. In Zr doped samples, the expansion of the unit cell destabilizes Li coordination at M1 sites; however, in Al doped samples, the increment of Li amount enhances Li–Li repulsions. In both cases, creation of vacancies at M1 sites increases Li mobility.