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

Ceramics with III-IV pyrochlore compositions, A 3 + 2B 4 + 2O 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 2 Sn 2 O 7 and Gd 2 Hf 2 O 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 2 Sn 2 O 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 1 5 ions/cm 2 ) at room temperature and a critical amorphization temperature of approximately 350 K. Gd 2 Hf 2 O 7 does not become amorphous at a dose of approximately 4.54 displacement per [lattice] atom (3.13 x 10 1 5 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 2 Sn 2 O 7 emphasize the importance of bond type, particularly the covalency of the (Sn-O) bond in determining the radiation response.

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