Structural modifications in pyrochlores caused by ions in the electronic stopping regime
Damage caused by swift heavy ions with three different electronic stopping powers (120 MeV Au9+ (22 keV/nm), 90 MeV I7+ (17 keV/nm) and 70 MeV Ni5+ (11 keV/nm)) in three pyrochlores (Gd2Zr2O7, Nd2Zr2O7 and Gd2Ti2O7) with progressively increasing radius ratios (r(A)/r(B) of A(2)B(2)O(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 Gd2Ti2O7 at the lowest S-e used, and a transition to anion-deficient fluorite (Fm (3) over barm) structure with about 1% decrease in volume in Nd2Zr2O7 and Gd2Zr2O7 at higher S-e. In Nd2Zr2O7 this is followed by amorphization and Gd2Zr2O7 does not amorphize even at the highest S-e employed. Raman analysis of Gd2Zr2O7 and Nd2Zr2O7, 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. Published by Elsevier B.V.