Heavy Ion Irradiation of Zirconate Pyrochlores

Abstract

Zirconate pyrochlores, A2Zr2O7, are important potential nuclear waste forms for Puimmobilization. The binary Gd2(Ti2-xZrx)O7 has been shown to have increasing resistance to ionirradiation damage with the increasing Zr content, and Gd2Zr2O7 is radiation resistant to a 1 MeV Kr+ ion irradiation at 25 K to a dose of 5 dpa. In this study, a 1.5 MeV Xe+ irradiation was completed for zirconate pyrochlores A2Zr2O7 (A=La, Nd, Sm, Gd). The radiation resistance decreases with an increase of the ionic radius of A-site cation. La2Zr2O7 is the first zirconate pyrochlore to be amorphized by ion beam irradiation, and the critical amorphization temperature, Tc, is ∼310 K. The susceptibility of La2Zr2O7 to ion beam damage is related to its structure, which shows the largest deviation from the ideal fluorite structure. These results are also consistent with calculations of the cation antisite formation energy in the pyrochlore structure. The ion irradiation-induced pyrochlore-to-fluorite transformation occurred in all of the irradiated zirconate pyrochlore phases. Based on the results for Gd2Ti2-xZrxO7 and A2Zr2O7, the defect fluorite structures are stable when the ionic radii ratio rA/rB≤1.54; beyond this limit, the defect fluorite structure becomes increasingly unstable relative to the amorphous state.

The solubility of cerium in La2Ti2O7 by DFT + U calculations

“…For an ideal pyrochlore structure, the value of x would be 0.3125 and 0.375 for the compositions with larger 48f oxygen positional parameter x are more resistant to ion beam-induced amorphization[4,[44][45][46]. This study indicates that the substitution of Ce for La in La 2 Ti 2 O 7 decreases the stability of La 2 Ti 2 O 7 and may result in increased radiation resistance.…”

Persistent Structure and Frustrated Magnetism in High Entropy Rare‐Earth Zirconates

“…Amongst the many oxide systems, the large family of pyrochlore oxides (A 2 B 2 O 7 ), stands out as an important functional materials class for many technological applications due in part to its substantial structural and chemical flexibility. [ 21 ] RE 2 Zr 2 O 7 (RE = Sc, Y, and La‐Lu), have received intense interest recently due to demonstrations of quantum frustrated magnetism, [ 22,23 ] nuclear waste containment, [ 24,25 ] fast ion conduction, [ 26 ] as solid electrolytes, [ 27 ] and as vehicles for theranostic (combined therapeutic and diagnostic) treatment. [ 28 ] For the so‐called 3–4 compositions (composed of equal parts RE with +3 valence and Zr with +4 valence), distinct structural motifs emerge depending on the ratio of the cation radii; an ordered pyrochlore‐structure (, typically written as RE 2 Zr 2 O 7 ) or disordered defect fluorite structure (, typically written as RE 0.5 Zr 0.5 O 1.75 ) can be stabilized.…”

Insight Into Disorder, Stress and Strain of Radiation Damaged Pyrochlores: A Possible Mechanism for the Appearance of Defect Fluorite

“…Pyrochlores cover a large variation of compositions ( Subramanian et al, 1983 ) and there have been numerous publications that endeavor to understand the tolerance pyrochlores have to radiation damage ( Lian et al, 2002 ; Sattonnay et al, 2008 ; Pilania et al, 2017 ; Holesinger et al, 2019 ). The reason for this goes well beyond the application to immobilize nuclear waste ( Lumpkin and Ewing, 1985 ; Ewing et al, 2004 ) and the subsequent amorphization ( Lang et al, 2009 ).…”

“…Characterization of the material is typically performed ex situ since ions are generally produced by an accelerator. One of the issues with using ions is that they have a very small interaction volume when compared with the bulk of the material and so typically produce a very thin layer and thus small amount of damaged material to be examined, utilizing techniques such as Glancing Incidence X-Ray Diffraction (GIXRD) ( Li et al, 2012 ) or Transmission Electron Microscopy (TEM) ( Lian et al, 2002 ). More recently there have been attempts to combine other techniques such as spectroscopy with GIXRD and TEM ( Lenz, 2019 ).…”