Synthesis and characterization of LnPO ₄ · nH ₂O (Ln = La, Ce, Gd, Tb, Dy) nanorods and nanowires

Aqueous precipitation method has been used to synthesize lanthanide orthophosphates LnPO ₄ · nH ₂O (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 LnPO ₄ hydrates (LnPO ₄ · nH ₂O) with hexagonal rhabdophane-type structure. The X-ray diffraction peaks and absorption of PO ₄ ^3- groups show a systematic shift from LaPO ₄ · nH ₂O to DyPO ₄ · nH ₂O due to the effect of lanthanide ionic contraction. The value of n in LnPO ₄ · nH ₂O 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.