On the composition and structure of lanthanum-, neodymium-and europium tantalates prepared from aqueous solutions

Composition and crystalline structures of solid phases have been determined which are formed during the interaction in systems K8Ta6O9-Ln(No3)3-H2O (Ln=La, Nd, En). The separation of tantalum from rare-earth elements in the composition studies was carried out by the oxalate method and the determinations were made by the gravimatric method (in the form of Ta2O5 and Ln2O3). The results of the analysis of solid phases indicate that their composition depends on the pH at which the precipitation takes place. This dependence is similar for all systems. It was found that at initial molar ratios Ta:Ln (>=) 4 and Ph > 10 hydrated metatantalates of rare-earth elements are products of the interaction. Neodymium and europium comoounds have cubic structure of the perowskite type, lanthanum compounds have the perowskite structure with tetragonal distortions