**5.6. REE vanadocalcic apatite**

The synthesis and physicochemical study of rare-earth-containing vanadocalcic oxyapatites where the pair Ca2+ and □ was substituted by Ln3+ and 1/2O2− was described by BENMOUSSA et al [139]. This substitution leads to lanthanum and praseodymium dioxyapatites Ca8Ln2(VO4)6O2, where Ln = La and Pr. Regarding rare earths such as neodymium, samari‐ um, europium, gadolinium and terbium, the Ln3+ content limit varies from one REE to another. It decreases when the REE ionic radius declines.
