Radiation Effects Of Perovskite Oxides:the Role Of Layered Structure And Structural Factors

Perovskites are regarded as promising high-level nuclear waste candidate immobilization matrices due to their excellent physical stability,chemical stability and radiation resistance.High-level nuclear waste has ultra-high radioactive,which requires a higher irradiation stability of the immobilization matrices.How to improve and predict the radiation resistance of perovskites is of great significance.Based on the radiation effect of perovskite oxides,two research work were studied:（1）the influence of layered structure on the irradiation behavior of perovskite was systematically studied for the first time based on Ruddlesden-Popper（RP）phase（SrTiO₃）_nSr O（n=1,2,3,∞）perovskites;（2）the correlation between radiation resistance and structural factors of perovskite oxides was explored based on ABO₃（A=Ca,Sr,Ba;B=Ti,Zr）perovskites.The first work in this paper is to explore the influence of layered structure on the irradiation behavior of RP phase（SrTiO₃）_nSr O（n=1,2,3,∞）perovskites.RP phase（SrTiO₃）_nSr O（n=1,2,3,∞）perovskite samples were prepared by solid-state reaction method,and the microstructure of the materials was characterized by X-ray diffraction,laser confocal Raman spectroscopy,transmission electron microscopy and scanning electron microscopy.The result shows that the prepared samples have a single phase without impurities.（SrTiO₃）_nSr O（n=∞）,i.e.,SrTiO₃ is cubic phase（lattice constant a=b=c）,（SrTiO₃）_nSr O（n=1,2,3）are all tetragonal phase（lattice constant a=b≠c）.The crystal plane spacing measured by transmission electron microscopy is consistent with the X-ray diffraction result,and the samples all have high crystallinity.The surface morphology of SrTiO₃ and（SrTiO₃）_nSr O（n=1,2,3）are spherical and rod-shaped respectively,which are consistent with their crystal structures of cubic phase and tetragonal phase.The lattice constant c value of（SrTiO₃）_nSr O（n=1,2,3）increases linearly with the increase of n value,which is consistent with the[Sr O]and[SrTiO₃]orderly stacking in RP phase（SrTiO₃）_nSr O（n=1,2,3）.In order to explore the structural evolution behavior of the samples under ion beam irradiation,the 3 Me V Xe ion was used to irradiate samples.The structure of the samples before and after irradiation was characterized by grazing incidence X-ray diffraction.（SrTiO₃）_nSr O（n=1,2,3,∞）underwent different degrees lattice swelling and amorphization under 3 Me V Xe ion irradiation at room temperature.For the same component,the relative variations of unit cell volume swelling and amorphous fraction gradually increase with the increase of ion fluence.Under the same ion fluence,the radiation resistance of（SrTiO₃）_nSr O（n=1,2,3,∞）is enhanced with the increase of n value（i.e.,decrease of the density of the Sr O layer for RP phase）.Under 3 Me V Xe ion irradiation at 350℃and 650℃,SrTiO₃ always maintained its original crystal structure,however,（SrTiO₃）_nSr O（n=1,2,3）gradually decomposed into SrTiO₃ and Sr O with the increase of temperature and ion fluence.The radiation resistance of（SrTiO₃）_nSr O（n=1,2,3,∞）also increased with the increase of n value at high-temperature ion beam irradiation.The samples of unirradiated and irradiated at room temperature were annealed at 350℃for 1 h,and the results showed that the phase transition of（SrTiO₃）_nSr O（n=1,2,3）under high temperature irradiation was the result of the synergistic effect of temperature and irradiation.In this part of the research work,the influence of the RP phase layered structure on the radiation resistance of the material at room temperature and high temperature was clarified.Another work in this paper is to study the correlation between radiation resistance and structural factors of perovskite oxides.Five ABO₃（A=Ca,Sr,Ba;B=Ti,Zr）perovskites with different structural factors were prepared by solid-state reaction method,and the microstructure of the materials was characterized by X-ray diffraction and scanning electron microscopy.The result show that each sample has a single phase without impurities.The sample has high density,uniform element distribution,and no element agglomeration.The crystal structure of the prepared samples is consistent with the crystal structure predicted by the structural factor.In order to evaluate the radiation resistance of five perovskites,the 3 Me V Xe ion were used to irradiate samples.The grazing incidence X-ray diffraction results showed that each component sample underwent different degrees of lattice swelling and amorphization under ion beam irradiation.Through the quantitative calculation of the relative variations of unit cell volume swelling and amorphous fraction,the radiation resistance of five perovskites was determined.It is found that the radiation resistance of ABO₃ perovskites is related to chemical components,that is to say,there exists ion-mass effect.The analysis results of irradiation experiments show that the radiation resistance of ABO₃ perovskite deteriorates with the increase of Goldschmidt’s tolerance factor（t）and（μ+t）^η（whereμis octahedral factor andηis atomic packing fraction）and decrease of new tolerance factor（τ）,except Sr Zr O₃.Furthermore,the conclusion obtained by irradiation experiments is verified by first-principles calculation from the perspective of thermodynamic stability.The result shows that the radiation resistance of ABO₃perovskites is inversely proportional to the thermodynamic stability,which is consistent with the result of pyrochlore oxide（another high-level waste immobilization matrices）.In other words,the radiation resistance of ABO₃ perovskites is closely related to structural factors,which provides a new idea to evaluate the radiation resistance of ABO₃ perovskites.That is to say,we can predict the ability to resist radiation damage of ABO₃ perovskites and construct new perovskite with high performance to resist radiation damage by structural factors.