Selective Formation of Yttrium Manganese Oxides through Kinetically Competent Assisted Metathesis Reactions

The synthesis of complex oxides requires high temperatures to overcome barriers imparted by solid-state diffusion; as such, reactions typically yield the most stable polymorph for a given composition. To synthesize new or metastable complex oxides, kinetically competent reactions with lower initial energy barriers must be devised to control the reaction pathway and resulting products. This contribution details the selective synthesis of different yttrium manganese oxides through assisted metathesis reactions between Mn2O3, YCl3, and A(2)CO(3) under flowing oxygen; where A = Li, Na, K. With lithium carbonate, the orthorhombic perovskite o-YMnO3 (o-YMnO3+delta) forms over the temperature range of 550-850 degrees C. With sodium carbonate, the pyrochlore Y2Mn2O7 forms at 650 degrees C. No apparent selectivity is observed with K2CO3, and all alkalis yields hexagonal YMnO3 at T > 950 degrees C. The alkali species modify the reaction pathway and thus impart kinetic control in the formation of both phases.