Synthesis of Hydroxyapatite Substituted by REE Ions (La³⁺, Ce³⁺), and Study of the Composition, Structure, and Properties of the Obtained Samples

Substituted apatites with a varying content of La³⁺ and Ce³⁺ ions are synthesized. The formation of substituted hydroxyapatite (La-HA, Ce-HA) is proved by XRD and IR spectroscopy. The change in the crystal lattice parameters of the synthesized phases is shown, which indicates the replacement of Ca²⁺ ions by REE ions in the hydroxyapatite structure. The presence of REE ions in solid phases is proved by ICP–AES. When studying the resorption of the synthesized samples, it is found that cation-substituted hydroxyapatites are less soluble than undoped HA.