Crystallization of mixed rare earth (didymium) molybdates in silica gel

Experiments on the growth of mixed rare earth (didymium-a combination of La , Nd, Pr and Sm) molybdates in silica gel medium are reported. The optimum conditions conducive for the growth of these crystals are described and dis cussed. Concentration programming is reported to enhance the size of crysta ls by two-fold; the maximum size obtained being about 1 mm(3). EDAX results suggest the crystals to be heptamolybdates of type R2Mo7O24, bearing compo sition La1.23Nd0.43Pr0.29 Sn0.05Mo7O24'. The didymium molybdate crystals as sume morphologies corresponding to those of spherulites, platelets, cuboids and coalesced crystals. Twinned structure in didymium molybdate crystals a re also reported. It is explained that spherulitic morphologies result from aggregates of crystals joining in a spherical envelope. It is suggested th at the crystals of didymium molybdates grow by two-dimensional spreading an d piling up of layers.