The effect of mixed alkali on structural changes and ionic migration characteristics in zinc borate glasses

The effect of mixed alkali on structural changes and ionic migration characteristics have been investigated in zinc borate glasses system with composition 5Al2O3-15ZnO-(15-x)K2O-xNa2O-65B2O3(x = 0,3,6,9,12,15mol%). The thermal properties including glass transition temperature (Tg), thermal expansion coefficient (α) and dilatometric softening temperature (Td) were determined by differential scanning calorimeter (DSC) and dilatometer. The ionic migration characteristics were investigated through dc conductivity and chemical stability, determined by electrochemical workstation and normalized mass losses (N(i)). And the glass structure was characterized by Fourier transform infrared spectroscopy, to explain the relationship between structure and properties. As the ratio of [Na2O]/([K2O]+[Na2O])(mol/mol) increase, the glass transition temperature (Tg), dilatometric softening temperature (Td), dc conductivity(σdc) and normalized mass losses (N(i)) of glass exhibit a nonlinear variation, deviate negatively from linearity, meanwhile thermal expansion coefficient (α) varies nonlinearly and deviates positively from linearity. From the FTIR studies the N4 values (fraction of tetrahedral coordinated boron atoms) exhibit a nonlinear variation, deviates negatively from linearity. These data clearly indicated the presence of strong mixed alkali effect (MAE) in the zinc borate glass system, and the MAE changes glass structure and inhibits ion migration.