Hexagonal CePO4 Research Articles

Formation of Monoclinic CePO4 by Aging Hexagonal CePO4 in an Aqueous Solution

Monoclinic CePO4 was formed by aging hexagonal CePO4 in the aqueous solution, whose pH range being 1-12, at above 50°C (Fig.2). The rate of formation of monoclinic CePO4 became high with decreasing pH and with increasing temperature. Hexagonal CePO4 gradually dis- appea'red as the aging progressed. For the formation of monoclinic CePO4 by aging hexagonal CePO4, about 90 days were necessary to keep it in the solution, whose pH being 1, and about 900 days in it, whose pH being 12, at 50°C. Monoclinic CePO4 crystals showed similar columnar shape as the starting hexagonal CePO4 (Fig.5). At 20°C, hexagonal CePO4 dissolved in the solution, whose pH being 1, after aging it for about 180 days, but it was stable in the solution, whose pH being above 2, after aging it for about 900 days.329