轻、重离子辐照烧绿石Lu_2Ti_2O_7导致的非晶结构变化

Radiation Effects of Light and Heavy Ion Irradiation on Amorphous Structure in Pyrochlore Lu_2Ti_2O_7

采用标准固相反应烧结法制备烧绿石结构的Lu_2Ti_2O_7.在室温下,用800keV Kr^(2+)和200keV He^+进行辐照.辐照后的样品采用掠入式X射线衍射(GIXRD)表征.结果表明:用800keV Kr^(2+)辐照样品时,辐照剂量达到2×10^(14)cm^(-2)(相应dpa(displacement per atom)为0.4)时,样品出现非晶化转变,并且随着辐照剂量的增加,非晶化转变量不断增加,增加至一定值后不再变化,未出现完全的非晶化转变;用200keV He^+进行辐照时,即使辐照剂量增加至2×10^(17)cm^(-2)(dpa为1.25),样品也没有出现非晶化转变.通过分子动力学模拟对结果进行分析后发现:重离子辐照时,样品在较小范围内产生较多的缺陷,且电子能损较低,样品温度增幅较小,缺陷复合率低,易导致非晶化转变;而轻离子辐照时结果相反.

The pyrochlore structure of Lu 2Ti2O7 was prepared by standard solid-state reaction sintering method.Pyrochlore pellets of Lu 2Ti 2O 7 were irradiated with 800 keV heavy Kr^2+and 200 keV light He+at room temperature.The microstructural evolution induced by different ion irradiation was observed using grazing incidence X-ray diffraction(GIXRD).The results showed that the phase transition of pyrochlore from ordered to partial amorphous was achieved under 800 keV Kr 2+irradiation with the fluence of 2×10^14 cm^-2(the corresponding dpa(displacement per atom)was 0.4).The percent of amorphization kept increasing with the increasing of the fluence,until it reached a certain value,but no complete amorphous transition was observed.However,a defected fluorite phase transformation was observed in the pyrochlore Lu 2Ti2O7 under 200 keV He+irradiation.No amorphous transition was observed even under 200 keV He+with a higher fluence of 2.0×10^17 cm^-2(dpa was 1.25).Then molecular dynamics simulation was performed to interpret the above observation.The simulation results showed that when the sample was irradiated by heavy ions,more defects ge-nerated in a smaller range,the electron energy loss was lower,the temperature of the sample increased less,the recombination rate of defect was lower and the amorphous transitions occured more easily,while for the light ion irradiation,the results exhibited conversely.