Ion Beam-Induced Amorphization of the Pyrochlore Structure-Type: A Review

Abstract

ABSTRACTThis paper reviews the recent developments in the understanding of the radiation-damage processes in A2B2O7 (Fd3m; Z=8) pyrochlore-structure compounds. Pyrochlore structure compounds display a wide range of behaviors in response to ion beam irradiation. Some compositions, such as Gd2Ti2O7, are amorphized at relatively low doses (∼0.2 dpa at room temperature) while other compositions, such as Gd2Zr2O7, do not amorphize (even at doses of 36 dpa at 25 K) and instead disorder to a defect fluorite structure. The response to ion beam irradiation is highly dependent on compositional changes that affect both the structural distortion from the ideal fluorite structure and the associated energetics of the disordering process. Generally, the ionic size of the cations plays a dominant role in determining the radiation response of different pyrochlore compositions. However, the cation ionic radius ratio criteria cannot be applied all-inclusively in predicting the radiation “tolerance” of a pyrochlore. Systematic irradiation studies of the radiation response of rare-earth (A-site) pyrochlores in which B = Ti, Zr, and Sn have shown that the behavior of the pyrochlore also depends on the cation electronic structure, i.e., the type of bonding, which is closely related to the polyhedral distortion and structural deviation from the ideal fluorite structure. These structural changes affect the dynamic defect recovery process directly linked to the material's response to and recovery from irradiation.