A novel additive-free oxides–hydrothermal approach for monazite-type LaPO₄ nanomaterials with controllable morphologies

A facile oxides–hydrothermal (O–HT) method is demonstrated to prepare high-purity monazite-type LaPO₄ nanomaterials. In this approach, La₂O₃ and P₂O₅ powder are first directly used as precursors under additive-free hydrothermal conditions. The as-prepared samples are characterized with X-ray diffraction, Fourier transform IR spectroscopy, thermogravimetry, scanning electron microscopy, transmission electron microscopy (high-resolution TEM, energy dispersive spectroscopy) and selected-area electron diffraction. The typical sample obtained at 433 K in 24 h comprises uniform single-crystal nanofibres with a diameter of ∼15–28 nm and an aspect ratio of 30–50. The influences of treatment time, synthesis temperature and P/La molar ratio are investigated. The phase transition from hexagonal hydrate to monoclinic anhydrous lanthanum phosphate and the growth process of nanofibres are revealed by the experimental results. The formation mechanism of the monoclinic LaPO₄ is discussed. The result indicates that the P/La ratio does not influence the composition and crystal phase but changes the morphology of the product in the O–HT system.