Optimization of synthesis conditions for rare-earth titanate based oxygen ion conductors
Abstract High-density (Yb0.9Ca0.1)2Ti2O6.9, (Yb0.8Ca0.1Tb0.1)2Ti2O7 − δ, and (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ solid solutions have been prepared through co-precipitation followed by firing for 4 h at 1500 and 1550 °C, and their crystal structure (XRD), microstructure (SEM), and oxygen ion conductivity (impedance spectroscopy) have been studied in relation to the firing temperature and precipitant used. As in the case of (Yb0.9Ca0.1)2Ti2O6.9 and (Yb0.8Ca0.1Tb0.1)2Ti2O7 − δ, the optimal synthesis temperature for (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ is 1500 °C. The bulk oxygen ion conductivity of the pyrochlore-like solid solutions (Yb0.9Ca0.1)2Ti2O6.9 is a stronger function of synthesis temperature than that of the (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ and (Yb0.8Ca0.1Tb0.1)2Ti2O7 − δ solid solutions with more complex A sublattice. The rise of the synthesis temperature from 1500 to 1550 °C has detrimental effect on the grain boundary conductivity of the (Yb0.9Ca0.1)2Ti2O6.9 and (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ ceramics. That effect is connected with a considerable grain-boundary segregation of a calcium-containing phase in the (Yb0.9Ca0.1)2Ti2O6.9 and (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ. The bulk and grain boundary conductivity of (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ are independent of the precursor synthesis conditions (homogeneous and non-homogeneous co-precipitation).