Ceramics with III-IV pyrochlore compositions, A3+2B4+2O7 (A = Y and rare earth elements; B = Ti, Zr, Sn, or Hf), show a wide range of responses to ion-beam irradiation. To evaluate the role of the B-site cations on the radiation stability ofthe pyrochlore structure-type, Gd2Sn2O7 and Gd2Hf2O7 have been irradiated by1 MeV Kr+. The results are discussed in terms of the ionic size and type ofbonding of Sn4+ and Hf4+ and compared to previous results for titanate andzirconate pyrochlores. Gd2Sn2O7 is sensitive to ion beam–induced amorphizationwith a critical amorphization dose of approximately 3.4 displacements per atom(dpa) (2.62 × 1015 ions/cm2) at room temperature and a critical amorphization temperature of approximately 350 K. Gd2Hf2O7 does not become amorphous at adose of approximately 4.54 displacement per [lattice] atom (3.13 × 1015 ions/cm2) at room temperature, but instead is transformed to a disordered fluorite structure upon ion-beam irradiation. Although the radius ratio of the A- to B-site cations provides a general indication of the type of radiation response of different pyrochlore compositions, the results for Gd2Sn2O7 emphasize the importance of bond type, particularly the covalency of the 〈Sn–O〉 bond in determining the radiation response.
Comparison of Ion-Beam Irradiation Effects in X2YO4 Compounds