Nasicon-type compounds were investigated by using powder X-ray diffraction techniques and impedance spectroscopy. The Li2FeZr(PO4)3 was orthorhombic (Pbna; a = 0.8706, b = 0.8786, c = 1.2220nm) and the Li2FeTi(PO4)3 was orthorhombic (Pbca; a = 0.8557, b = 0.8624, c = 2.3919nm). They exhibited no phase transitions between room temperature and 800C. There were no slope variations in the Arrhenius plot, over the same temperature range. The activation energies for ionic conductivity were equal to 0.62 and 0.64eV for Li2FeZr(PO4)3 and Li2FeTi(PO4)3, respectively. In order to evaluate the present results, they were compared with those for the α- and β-Zr2Li(PO4)3 phases. A change in activation energy, from 0.47 to 1.03eV, was observed in the case of the β-phase at about 300C. This was attributed to an orthorhombic to monoclinic phase transition. In the case of the α-phase, the activation energy was equal to 0.47eV at 150 to 850C.

Structural and Electrical Characterization of NASICON-Type Li2FeZr(PO4)3 and Li2FeTi(PO4)3 Compounds. R.Ruffo, C.M.Mari, M.Catti: Ionics, 2001, 7[1-2], 105-8