Amorphization of Ca₈LnNa(PO₄)₆F₂(Ln=La, Nd and Sm) Apatite Ceramics Induced by Kr Ion Irradiation

The apatite structure material Ca₈LnNa(PO₄)₆F₂(Ln=La, Nd and Sm) were successfully synthesized by the solid state reaction method, and the single phase was confirmed by normal X-ray diffraction(XRD). Three kinds of samples were irradiated with 800 keV Kr²⁺ at room temperature, then the irradiated samples were characterized by grazing incidence X-ray diffraction(GIXRD) to identify the structures of irradiation layer. Crystalline to amorphization phase transition was observed in these three kinds of samples within the irradiation dose (1.0×10¹⁴~7.0×10¹⁴ cm^-2). However, the abilities to resist amorphization of the three samples are different, the relationship of the ability to resist amorphization is Ca₈LaNa(PO₄)₆F₂ > Ca₈NdNa(PO₄)₆F₂ > Ca₈SmNa(PO₄)₆F₂. The ion radius of the lanthanide nuclides in Ca₈LnNa(PO₄)₆F₂ are more smaller, more lanthanide nuclides will occupy the Ca(2) positions and form ionic bonds with F. Meanwhile, the ionic bonding between lanthanide nuclides and Ca are weaker than Ca-F. Therefore, the ion radius of the lanthanide nuclides are more smaller, the more point defects will remain under irradiation, and the crystalline to amorphous phase transition is more likely to occur.