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

[摘要] Experiments on the growth of mixed rare earth (didymiumâ€�?�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 discussed. Concentration programming is reported to enhance the size of crystals by two-fold; the maximum size obtained being about 1 mm³. EDAX results suggest the crystals to be heptamolybdates of type R₂Mo₇O₂₄, bearing composition La_1.23Nd_0.43Pr_0.29 Sm_0.05Mo₇O₂₄. The didymium molybdate crystals assume morphologies corresponding to those of spherulites, platelets, cuboids and coalesced crystals. Twinned structure in didymium molybdate crystals are also reported. It is explained that spherulitic morphologies result from aggregates of crystals joining in a spherical envelope. It is suggested that the crystals of didymium molybdates grow by two-dimensional spreading and piling up of layers.

[学科分类] 材料工程

[关键词] Crystal growth;didymium molybdate;gel method;morphology;EDAX.