Polymorphism in yttrium molybdate Y2Mo3O12

Yttrium molybdate (Y2Mo3O12) has been prepared by non-hydrolytic sol–gel chemistry. The phase evolution upon heating was investigated using in situ and ex situ heat treatments combined with powder X-ray diffraction. This method has led to the isolation of two orthorhombic phases with different atomic connectivity. Yttrium adopts 6- and 7-coordinate sites in the Pbcn and Pba2 structures, respectively. Cocrystallization of both phases was observed in a narrow temperature range, suggesting that crystallization kinetics play a major role in phase formation. It was found that the Pba2 phase is the stable polymorph below 550 °C, and converts to Pbcn at higher temperatures.

Yttrium molybdate (Y2Mo3O12) prepared by non-hydrolytic sol–gel chemistry crystallizes in a mixture of orthorhombic polymorphs with different atomic connectivities. The Pbcn and Pba2 phases coexist over a narrow temperature range. Crystallization of the Pbcn structure is kinetically favored. The Pba2 polymorph is the thermodynamically stable phase at low temperatures, and converts to Pbcn above 550 °C.Figure optionsDownload as PowerPoint slide