Synthesis of lithium conducting titanium phosphates by the sol-gel process

The synthesis of titanium and lithium phosphates was studied using the sol-gel method. Particular attention was paid to phosphate precursors, which were mixtures of phosphate mono- and diesters prepared by solvolysis of P₄O₁₀ in isopropanol. The reaction of these precursors with titanium and lithium alkoxides yielded homogeneous gels and after drying and thermal cleavage of the esters at 300 °C, amorphous inorganic products. For the composition corresponding to the stoichiometric formula of a stable compound such as LiTi₂(PO₄)₃, the phase crystallized as early as 550 °C by nucleation from the amorphous mixture. Ionic conductivity measured at room temperature was of the order of 10⁻⁵ S·cm⁻¹ which increased after heat treatment at higher temperatures. If the composition did not correspond to a stable thermodynamic phase, phase separation occurred, and ionic conductivity decreased between 500 °C and 700 °C.