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

Abstract In vanadocalcic oxyapatite Ca 10 (VO 4 ) 6 O□, the pair (Ca 2+ , □) can be substituted by the pair (Ln 3+ , 1/2O 2− ) (Ln 3+ 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 La 3+ and Pr 3+ ions and leads to lanthanum or praseodym dioxyapatites Ca 8 Ln 2 (VO 4 ) 6 O 2 (Ln = La, Pr). With regards to rare earths such as neodym, samarium, europium, gadolinum, and terbium, the Ln 3+ content limit varies from one rare earth to another. It decreases when the rare-earth ionic radius declines.