Glasses with formula Na3-xLixCaTi(PO4)3 [10(3-x) mol. % Na2O - 10x mol. % Li2O - 20 mol. % CaO - 20 mol. % TiO2 - 30 mol. % P2O5] (0 ≤ x ≤ 3) were prepared by standard melt-quenching technique, and their structural and physical properties were characterized by thermal analysis, density measurements, Raman, and impedance spectroscopy. When Na+ is gradually replaced by Li+ , molar volume, glass transition temperature (Tg) and ionic conductivity values decrease, pass through a minimum around the composition x = 1.5, then increase, while density values increase, pass through a maximum, then decrease. The non-linear variation of these physical properties is a result of the classical mixed alkali effect. Powder X-ray diffraction shows that crystallization of the glasses leads to the formation of a Nasicon phase for the compositions x = 0 and x = 0.5, and to a mixture of phases for the other compositions. Raman spectroscopy study shows that the glass structure contains P2O7 and PO4 groups, and short -Ti-O-Ti-O-Ti- chains, formed by TiO6 octahedra linked to each other through corners. These chains are linked by phosphate tetrahedra to form -O-Ti-O-P-O- linkages.
Synthesis, structural characterization and ionic conductivity of mixed alkali titanium phosphate glasses