Bubble Formation in Apatite Structures by He-Ion Irradiation at High Temperature

Apatite ceramics Ca_10(PO_4)_6X_2 (X=F, OH) were prepared by the standard solid state sintering method and irradiated with He ions under a fluence of 5\times 10^16 ions/cm^2 at 450 ^\circ\!C. Irradiation induced formation and growth of the He bubbles were observed by a transmission electron microscope. Hydroxyapatite Ca_10(PO_4)_6(OH)_2 and fluoroapatite Ca_10(PO_4)_6F_2 with different He bubble morphologies indicate the influence of OH^-/F^- substitution on the He-ion annealing efficiency, as well as the structure itself, which affects the process of He bubble evolution and formation. The grain boundaries also act as sinks to accumulate He bubbles. No obvious irradiation damage but slight intensity reduction and left shift of diffraction peaks were observed according to the grazing incidence x-ray diffraction and Raman spectra characterizations, indicating that defects of interstitials and vacancies were generated.