The Study Of Irradiation-induced Amorphization Properties Of Apatite Structure (Ca_10-2xLn_xNa_x?PO₄?₆F₂) Materials

The operation of nuclear power plants has alleviated the energy shortage in some areas,but the nuclear waste generated during the reactor operation need to be disposed carefiully.It is a very important reference for the material to maintain good structural stability in an irradiated environment when we selecting a material as a solidification matrix for nuclear waste.The apatite structure(Ca10(PO4)6F2)material has been considered by many scholars as a very potential host phases for actinide immobilization and fission products due to the excellent physical properties and good inclusiveness to radioactive elements.In this paper,the effects of different lanthanide elements and the different contents of solidified lanthanides on the ability of irradiation-induced amorphization of apatite structure materials were studied.Considering that the actinides are radioactive,the lanthanides are safer and the lanthanide chemical properties are very close to the actinides.So the lanthanides were used to simulate the actinides in the apatite structure.Two series of apatite structural ceramic sample Ca8LnNa(PO4)6F2(Ln=La,Nd and Sm)and Cai0-2xLaxNax(PO4)6F2(X=0.2,1 and 2)were successfully synthesized by conventional solid state reaction method.All samples were characterized by conventional X-ray diffraction(XRD)to confirm that each material was a well-crystallized and single apatite structure.The samples were polished,and all samples were irradiated at room temperature with 800 keV Kr2+.The irradiated samples were characterized by grazing incidence X-ray diffraction(GIXRD)and transmission electron microscope(TEM)to characterize the structural information of the damaged layer.It was found that in the Ca8LnNa(PO4)6F2(Ln=La,Nd and Sm)materials,crystalline to amorphization phase transition was observed in these three kinds of samples within the irradiation fluence(1.0×1014 Kr2+/cm2?7.0×1014 Kr2+/cm2).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 nuclide in CasLnNa(PO4)6F2 is smaller,more lanthanide nuclides will occupy the Ca(2)positions and form ionic bonds with F-which are weaker than Ca-F.Therefore,the ion radius of the lanthanide nuclide is smaller,the more point defects will remain during irradiation,and the crystalline to amorphous phase transition is more likely to occur.In the study of the effect of La content on the abilities to resist amorphization of apatite structure samples,the irradiation fluence are ranging from 5.0×1013 Kr2+/cm2 to 7.0×1014 Kr2+/cm2 in the Ca10-2xLaxNa,(PO4)6F2(X=0.2,1 and 2)samples.It was found that there is no crystalline to amorphous phase transition occurred in the three materials at the fluence of 5.0×1013 Kr2+/cm2,but the unit cell became bigger due to the defects formation.When the fluence increased to 1.0×1014 Kr2+/cm2,the crystalline to amorphous phase transition began to occurred in all three samples,and the amorphous contents of the three materials were different at each irradiation fluence,which means that their abilities to resist amorphization are different.However,the sample with the highest La content Ca6La2Na2(PO4)6F2 has more La occupied the Ca(1)position,showing better ability to resist amorphization,and the sample with the lowest La content Ca9.6La0.2Na0.2(PO4)6F2 has the worst ability to resist amorphization.