Influence of ionic radius of alkaline-earth metals in ion conducting 2(Ca, Sr, Ba)O2TiO2SiO2 glasses

We have studied the relationship between ionic conductivity and the ionic radius of A site in 2AO2TiO2SiO2 (ATSO; ACa, Sr and Ba) glasses. Electrical measurements were carried out in the frequency range 100 Hz ~ 30 MHz and temperature range 300-540 °C. Raman spectroscopy and differential thermal analysis measurements were also performed. The exponents of the Cole-Cole plot, power-law conductivity and modulus formalisms reveal the nature of ionic transport and the conductivity relaxation. Raman spectroscopic data of ATSO glasses clarify the modification of vibrational networks of silicate and titanate complexes by alkaline-earth metals (Ca, Sr and Ba). The ratio of non-bridging oxygens per tetrahedrally coordinated cations (NBO/T) in the 2CaO and 2SrO2TiO2SiO2 glasses decreases rapidly, suggesting polymerization of the silicate and titanate networks. The disorder of the glass matrix in 2BaO2TiO2SiO2 glass is greatly reduced with increasing non-bridging oxygens per NBO/T and decreasing interionic Coulomb interactions. The conduction mechanisms of dc and ac for all ATSO glasses are the same but the ions hop through a different fractal structured conduction pathway. The dimension of ionic conduction pathway decreases with increasing ionic radius of alkaline-earth metals in ATSO glasses.