Role of ion species in radiation effects of Lu2Ti2O7 pyrochlore

Abstract

In an attempt to investigate the role of ion species in the radiation effects of pyrochlores, polycrystalline Lu 2 Ti 2 O 7 samples, prepared through a standard solid state process, were irradiated with three different ion beams: 400 keV Ne 2+ , 2.7 MeV Ar 11+ and 6.5 MeV Xe 26+. To characterize the damaged layers in Lu 2 Ti 2 O 7 , the grazing incident X-ray diffraction technique was applied. All the three irradiations induce significant amorphization processes and lattice swelling in Lu 2 Ti 2 O 7. However, when the ion fluence is converted to a standard dose in dpa, the radiation effects of Lu 2 Ti 2 O 7 show a great dependence on the implanted ion species. The threshold amorphization dose decreases with increasing ion mass and energy. Besides, the amorphization rate, as well as lattice swelling rate, increases with increasing ion mass and energy. That is, the Lu 2 Ti 2 O 7 pyrochlore is more susceptible to amorphization and lattice swelling under heavier ion irradiation. These results are then discussed in the framework of defect configuration and the density of collision cascades based on Monte Carlo simulations.

Structural evolution of Lu2‐xCexTi2O7 pyrochlores under 400 keV Ne irradiation

“…The GIXRD patterns of Lu 1.6 Ce 0.4 Ti 2 O 7 at different doses and LCTO with varying Ce‐concentrations at a dose of 0.185 dpa are presented in Figure 2A,B. As shown in Figure 2A, at dose of 0.037 dpa, Lu 1.6 Ce 0.4 Ti 2 O 7 began to swell in the pre‐amorphous stage as all the diffraction peaks shifted to lower values of 2θ, consistent with previous studies 30,34,40 . The lattice swelling of irradiated pyrochlore is mainly caused by cation antisite defects, and the antisites are formed directly in cascades 30 …”

“…The threshold displacement energies for Lu, Ce, Ti and O atom were set as 84, 205, and 52 eV, respectively. 40,41 The maximum displacement damage depth is ~400 nm, which is much greater than the depth that the GIXRD technique can detect. The doses at 200 nm depth were estimated by the SRIM simulation to match the depth of the X-ray calculated by HighPoint software, which is 150 nm at the incident angle of 0.5°.…”

“…The penetration depth and the implanted ion range were simulated by the SRIM‐2013 code, 39 as shown in Figure 1. The threshold displacement energies for Lu, Ce, Ti and O atom were set as 84, 205, and 52 eV, respectively 40,41 . The maximum displacement damage depth is ~400 nm, which is much greater than the depth that the GIXRD technique can detect.…”

“…As shown in Figure 2A, at dose of 0.037 dpa, Lu 1.6 Ce 0.4 Ti 2 O began to swell in the pre-amorphous stage as all the diffraction peaks shifted to lower values of 2θ, consistent with previous studies. 30,34,40 The lattice swelling of irradiated pyrochlore is mainly caused by cation antisite defects, and the antisites are formed directly in cascades. 30 As the dose increases to 0.185 dpa, the swollen pyrochlore phase transformed to a mixture of pyrochlore and disordered fluorite, identified by the splitting of all the fundamental fluorite diffraction maxima.…”

“…Similar phenomena have been reported and explained as the result of the formation of cation antisite defects. 30,35,40 Titanate pyrochlores can experience significant radiation-induced cation disordering, leading to substantial unit cell expansion at low doses.…”