LAUSR

Abstract The inluence of the heat treatment conditions and of the time of hydrothermal treatment at 210°С on the phase composition and size of crystallites and nanoparticles of lanthanum orthophosphate (LaPO 4 ) was considered. The heating conditions in the course of hydrothermal synthesis of LaPO 4 influence the structural transition of lanthanum orthophosphate of rhabdophane structure into the phase of monazite structure, and also the particle morphology and crystallite size. The phase of monazite structure with the crystallite size of approximately 12 nm without rhabdophane impurity is formed after hydrothermal treatment at 210°С for 30 min in the case of microwave heating of the hydrothermal fluid. When using external heating of autoclaves, at the same temperature inside the autoclave, the mean size of the crystallites of the monazite phase formed is 17 nm.