The incorporation of chromium (III) into hydroxyapatite crystals

•We analysed the formation and morphology of HAP crystals doped with chromium.•We studied the Cr ion local symmetry into hydroxyapatite host structure.•When the Cr concentration is increased to 18 mol% Cr2O3 and Cr 6+ is formed.•It is not clear the Cr replace Calcium sites preference into hydroxyapatite.•We report interstitial oxygen atoms as possible charge compensation mechanism.

Nanocrystals of hydroxyapatite (HAP) powder with different Cr3+ molar concentrations were synthesized using the co-precipitation method and a rod-like morphology was observed. Powder characterization results indicate the use of dopant influence in the HAP hexagonal phase formation, other Cr-containing phases and a charge compensation mechanism. By X-ray absorption spectroscopy, the local coordination structure of Cr incorporated into HAP was examined. X-ray absorption near-edge structure (XANES) spectroscopy results suggest Cr takes a different valence for the incorporated Cr concentrations. X-ray absorption fine structure (EXAFS) fitting confirms that Cr occurs in octahedral coordination as chromium local behaviour in Cr2O3 and can replace both Ca1 and Ca2 sites.