Synthesis of monodispersed LaPO₄ particles using the hydrothermal reaction of an La(edta)^- chelate precursor and phosphate ions

Homogeneous precipitation of LaPO₄ was carried out using the hydrothermal reaction of lanthanum(III) ethylenediamine tetraacetate complex (La(edta) ) and phosphate ion in order to prepare directly monodispersed crystalline LaPO₄ particles. Monodispersed monazite-type LaPO₄ precipitated under conditions of 0.008 M La³⁺, [edta]/[La]≥2 and [PO₄]/[edta] = 0.6 to 1 at 150 °C for 2 h. The particle consisted of fine crystals ca. 20 nm in length. The spherical particle of 0.3 μm diameter precipitated at pH 3, and the spindle-like particle precipitated with decreasing [edta]/[L³⁺] molar ratio or increasing pH to 7. The monodispersed particle may be formed by control of the precipitation rate, depending on the stability of the La(edta)^- chelate precursor determined by [edta]/[PO₄] and pH.