Synthesis and physicochemical study of new rare-earth-containing vanadocalcic oxyapatites

In vanadocalcic oxyapatite Ca10(VO4)6O□, the pair (Ca2+, □) can be substituted by the pair (Ln3+, 1/2O2−) (Ln3+ is a rare-earth ion). In theory, this substitution allows for introducing up to two rare-earth ions into the apatitic lattice. However, a limitation of this substitution depending on the nature of rare-earth was observed. Thus, this substitution is maximum in the case of La3+ and Pr3+ ions and leads to lanthanum or praseodym dioxyapatites Ca8Ln2(VO4)6O2 (Ln = La, Pr). With regards to rare earths such as neodym, samarium, europium, gadolinum, and terbium, the Ln3+ content limit varies from one rare earth to another. It decreases when the rare-earth ionic radius declines.