The XPS data clearly indicates that the HA nanoparticles used in this experiment are deficient in calcium (Ca/P ratio=1.37). This could explain why the HA decomposition occurs before 1200 °C since deficient HA start their decomposition at temperatures lower than pure HA (ratio=1.67) [19]. In the literature, this decomposition is described as partial although the reason remains unknown. The commonly accepted decomposition reaction for deficient HA isCa10(PO4)6(OH)2→3Ca3(PO4)2+CaO+H2O
Ca/P
ratio
1.37
HA decomposition
occurs
before 1200 °C
°C
deficient HA start their decomposition at temperatures lower than pure HA
ratio
1.67