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

Abstract

Abstract Ytterbium titanate pyrochlore, Yb 2 Ti 2 O 7 , was prepared by molten salt mediated synthesis (MSS) from titanium oxide (TiO 2 ) and ytterbium oxide (Yb 2 O 3 ) 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 TiO 2 particle size were explored. Synthesis temperatures and times required for formation of single phase Yb 2 Ti 2 O 7 were found to be lower than those required for solid state synthesis (SSS). Whereas MSS synthesis of single phase Yb 2 Ti 2 O 7 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. Yb 2 Ti 2 O 7 micron-sized powder prepared by MSS showed similar particle size and morphology to that of the TiO 2 precursor demonstrating a template growth mechanism. However, the use of TiO 2 nano-sized powder changed the dominant synthesis mechanism from template growth to dissolution–precipitation and facilitated synthesis of near single phase Yb 2 Ti 2 O 7 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 Yb 2 Ti 2 O 7 by molten salt mediated synthesis from TiO 2 and ytterbium chloride (YbCl 3 ) reagents.