Krypton ion irradiation-induced amorphization and nano-crystal formation in pyrochlore Lu₂Ti₂O₇ at room temperature

Polycrystalline pyrochlore Lu₂Ti₂O₇ pellets are irradiated with 600-keV Kr³⁺ ions up to a fluence of 1.45× 10¹⁶ Kr³⁺/cm². Irradiation induced structural modifications are examined by using grazing incidence x-ray diffraction (GIXRD) and cross-sectional transmission electron microscopy (TEM). The GIXRD reveals that amorphous fraction increases with the increase of fluences up to 2× 10¹⁵ Kr³⁺/cm², and the results are explained with a direct-impact model. However, when the irradiation fluence is higher than 2× 10¹⁵ Kr³⁺/cm², the amorphous fraction reaches a saturation of ～ 80%. Further TEM observations imply that nano-crystal is formed with a diameter of ～ 10 nm within the irradiation layer at a fluence of 4×10¹⁵ Kr³⁺/cm². No full amorphization is achieved even at the highest fluence of 1.45× 10¹⁶ Kr³⁺/cm² (～ 36 displacement per atom). The high irradiation resistance of pyrochlore Lu₂Ti₂O₇ at higher fluence is explained on the basis of enhanced radiation tolerance of nano-crystal structure.