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 A₂CO₃ under flowing oxygen; where A = Li, Na, K. With lithium carbonate, the orthorhombic perovskite o-YMnO₃ (o-YMnO_3+δ) forms over the temperature range of 550-850 °C. With sodium carbonate, the pyrochlore Y₂Mn₂O₇ forms at 650 °C. No apparent selectivity is observed with K₂CO₃, and all alkalis yields hexagonal YMnO₃ at T > 950 °C. The alkali species modify the reaction pathway and thus impart kinetic control in the formation of both phases.