Rapid low temperature synthesis of a titanate pyrochlore by molten salt mediated reaction

Ytterbium titanate pyrochlore, Yb2Ti2O7, was prepared by molten salt mediated synthesis (MSS) from titanium oxide (TiO2) and ytterbium oxide (Yb2O3) reagents. Potassium and sodium chloride mixtures were used as the molten salt medium and the effects of salt to reagent ratio, salt composition, synthesis temperature, reaction time, and TiO2 particle size were explored. Synthesis temperatures and times required for formation of single phase Yb2Ti2O7 were found to be lower than those required for solid state synthesis (SSS). Whereas MSS synthesis of single phase Yb2Ti2O7 was achieved with micron-sized powders after a single reaction at 1200 °C for 1 h, SSS with micron-sized powders required an extended reaction time of 36 h at 1350 °C. Yb2Ti2O7 micron-sized powder prepared by MSS showed similar particle size and morphology to that of the TiO2 precursor demonstrating a template growth mechanism. However, the use of TiO2 nano-sized powder changed the dominant synthesis mechanism from template growth to dissolution-precipitation and facilitated synthesis of near single phase Yb2Ti2O7 at the remarkably low temperature of 700 °C in only 1 h. The potential application for lanthanide and actinide immobilisation from molten salt reprocessing wastes was demonstrated by preparation of Yb2Ti2O7 by molten salt mediated synthesis from TiO2 and ytterbium chloride (YbCl3) reagents.