Structural evolution of Lu_2‐xCe_xTi₂O₇ pyrochlores under 400 keV Ne irradiation

Abstract

Lu2‐xCexTi2O7 (LCTO) pyrochlores were irradiated by 400 keV Ne2+ with fluences (dose) of up to 5 × 1015 ions/cm2 (1.875 dpa). The detailed damage process was investigated by combining grazing incident angle X‐ray diffraction (GIXRD) and transmission electron microscopy (TEM). Subsequent to the 2% volume swelling at a fluence of 1 × 1014 ions/cm2 (0.037 dpa), the initially swollen LCTO pyrochlore formed both a disordered fluorite phase and a nanocrystalline pyrochlore phase at a fluence of 5 × 1014 ions/cm2 (0.185 dpa). At higher fluences, the fluorite phase diminished as amorphous domains increased in volume when the dose reached a fluence of 1 × 1015 ions/cm2 (0.371 dpa), while the nanocrystalline pyrochlore phase persisted. At the highest fluence of 5 × 1015 ions/cm2 (1.854 dpa), the amorphous fraction decreased, meanwhile the degree of crystallinity of nanocrystalline pyrochlore phase was enhanced, as evidenced by the increased intensity of superlattice diffraction maxima. The phase transformation and recrystallization can be explained by the release of strain in irradiation‐induced swollen pyrochlore crystallites. The evolution of the damage process is mainly driven by the differences in the Gibb's free energies of fluorite phase as compared with the pyrochlore phase as a function of grain size. We have demonstrated that ion beam techniques can be used to manipulate the phase stability and crystallite size of pyrochlore. These results provide the basis for tailoring the mechanical strength and response of pyrochlores to extreme radiation environments.

Pressure-induced phase transition of Lu2Ti2O7 and Lu1.5Ce0.5Ti2O7+x pyrochlores

“…Two typical defect formation mechanisms in pyrochlore are reported in studying the phase transitions in pyrochlores under pressure: The first one is the cation position swap to form anti-situ defects, which leads to A 3+ and B 4+ cation disorder, the second defect formation mechanism is that the 48f oxygen ions move to 8b oxygen vacancies to form Frenkel defect pairs, which leads to anion-lattice disorder and a pyrochlore phase transition [8,25]. Similar phase transition mechanisms are also found in studies of irradiation [33][34][35][36], high temperatures [37] in pyrochlore.…”

Mechanical and Structural Response of Radiation-Damaged Pyrochlore to Thermal Annealing

“…It was found that the ordered pyrochlore structure first transforms into an anion-disordered pyrochlore structure and at higher fluences into a cation-disordered fluorite structure [47] . Recently, Xia et al [48] reported the interesting case of ion irradiation related recrystallization processes at higher fluences in Lu 2-x Ce x Ti 2 O 7 pyrochlore phases. Janish et al [49] investigated in-situ the recrystallization of an irradiated pyrochlore phase using transmission electron microscopy.…”