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]greater than or equal to 2 and [PO4]/[edta] = 0.6 to 1 at 150 degrees C for 2 h. The particle consisted of fine crystals ca. 20 nm in length. The spherical particle of 0.3 mu m 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 central of the precipitation rate, depending on the stability of the La(edta)(-) chelate precursor determined by [edta]/[PO4] and pH.