Synthesis and characterization of LnPO4 x nH2O (Ln = La, Ce, Gd, Tb, Dy) nanorods and nanowires.

Aqueous precipitation method has been used to synthesize lanthanide orthophosphates LnPO4 x nH2O (Ln = La, Ce, Gd, Tb, Dy) with high purity and yield. It has been shown by XRD, TGA, and FTIR characterization that the as-synthesized samples are the LnPO4 hydrates (LnPO4 x nH2O) with hexagonal rhabdophane-type structure. The X-ray diffraction peaks and absorption of PO4(3-) groups show a systematic shift from LaPO4 x nH2O to DyPO4 x nH2O due to the effect of lanthanide ionic contraction. The value of n in LnPO4 x nH2O depends on the lanthanide element and synthetic condition. Field-emission scanning electron microscopy observations show the morphology of as-synthesized samples, which consist entirely of nanorods/nanowires with diameters of 30-100 nm and lengths ranging from several hundreds of nanometers to several micrometers. The anisotropic growth of crystals should be responsible for the formation of nanorods/nanowires, which is related to the hexagonal crystal structure.