Structural modifications in pyrochlores caused by ions in the electronic stopping regime

Abstract

Damage caused by swift heavy ions with three different electronic stopping powers (120 MeV Au 9+ (22 keV/nm), 90 MeV I 7+ (17 keV/nm) and 70 MeV Ni 5+ (11 keV/nm)) in three pyrochlores (Gd 2Zr 2O 7, Nd 2Zr 2O 7 and Gd 2Ti 2O 7) with progressively increasing radius ratios ( r A/ r B of A 2B 2O 7) of cations is reported. Since I +7 is one of the ions used, these measurements also simulate fission fragment damage in pyrochlores and identify a potential host lattice for inert matrix fuel. X-ray diffraction on the irradiated materials indicate amorphization in Gd 2Ti 2O 7 at the lowest S e used, and a transition to anion-deficient fluorite ( Fm 3 ¯ m ) structure with about 1% decrease in volume in Nd 2Zr 2O 7 and Gd 2Zr 2O 7 at higher S e. In Nd 2Zr 2O 7 this is followed by amorphization and Gd 2Zr 2O 7 does not amorphize even at the highest S e employed. Raman analysis of Gd 2Zr 2O 7 and Nd 2Zr 2O 7, indicate an increase of Zr coordination number after irradiation and the bands become broader due to disordering. Analysis of the results shows that the radiation susceptibility of these pyrochlores in the electronic stopping regime strongly depends on the radius ratio of A to B cations and hence on the energy required for formation of cation antisites and anion Frenkel pairs, similar to their susceptibility in the nuclear stopping regime.