Phases formation in cerium-doped hydroxyapatite

Cerium-substituted hydroxyapatites (Ce-HAs) with an estimated content of Ce3+ of 0; 0.1; 0.25; 0.5 mol. % were prepared by two different synthesis methods: precipitation from aqueous solutions of salts and mechanochemical synthesis. The powders after synthesis were heat-treated at 1250 °C to achieve well-crystallized phases. The X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), energy dispersive analysis (EDA), and dilatometry methods revealed that cerium ions didn’t not fully incorporate into the HA structure, but rather were transform to the CeO2 phase. It was attributed to the transition of Ce valency (III)→(IV) through the oxidation reaction under air conditions during materials heating. Two different synthesis methods provided similar phase composition of the obtained compounds, though different microstructure of the resulted ceramics. It was shown that cerium introduction prevents HA sintering during thermal activation, possibly due to contribution of large atomic mass of cerium ions and formation of cerium (IV) oxide at the crystal boundaries.