Cerous phosphate gels: Synthesis, thermal decomposition and hydrothermal crystallization paths

Since their discovery in the late 19th century, cerium (IV) phosphates have been a very poorly studied class of rare earth compounds. In this paper, a facile method of amorphous cerous phosphate gels preparation is proposed, starting from nanocrystalline ceria and allowing for large-scale synthesis of these compounds. The use of this method provides deeper insight into the chemical composition and structure of cerous phosphate gels, and enables the peculiarities of their crystallization under hydrothermal conditions in H2O and H3PO4 aqueous solutions to be traced. Only Ce+3 compounds crystallize in a neutral medium if they are present in the composition of the cerous phosphate gels. For Ce+4 compounds to crystallize, a significant amount of orthophosphoric acid should exist in a reaction mixture. These features are likely to be related to the fact that crystalline Ce+4 orthophosphates can only exist in the form of acid salts.