Ion-beam irradiation of Gd_2Sn_2O_7 and Gd_2Hf_2O_7 pyrochlore: Bond-type effect

摘要

Ceramics with Ⅲ-Ⅳ pyrochlore compositions, A_2~(3+)B_2~(4+)O_7 (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 of the pyrochlore structure-type, Gd_2Sn_2O_7 and Gd_2Hf_2O_7 have been irradiated by 1 MeV Kr~+. The results are discussed in terms of the ionic size and type of bonding of Sn~(4+) and Hf~(4+) and compared to previous results for titanate and zirconate pyrochlores. Gd_2Sn_2O_7 is sensitive to ion beam-induced amorphization with a critical amorphization dose of approximately 3.4 displacements per atom (dpa) (2.62 x 10~(15) ions/cm~2) at room temperature and a critical amorphization temperature of approximately 350 K. Gd_2Hf_2O_7 does not become amorphous at a dose of approximately 4.54 displacement per [lattice] atom (3.13 x 10~(15) ions/cm~2) 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 Gd_2Sn_2O_7 emphasize the importance of bond type, particularly the covalency of the bond in determining the radiation response.