Synthesis and Ion-Irradiation Tolerance of the Dy2TiO5 Polymorphs

Abstract

In developing improvements in nuclear fuels, work has been conducted in replacing boron with lanthanides to act as neutron absorbent materials. To further this development for the first time the three major polymorphs of Dy2TiO5 have been fabricated as bulk, single-phase materials in a systematic study. Crystal structure refinement has been carried out from powder x-ray diffraction data, with further structural detail attained via electron diffraction. A cubic phase, defect-pyrochlore, Fd-3m space group, was found with cell parameter a = 10.2996 (1) A and oxygen x48f positional parameter = 0.331 (1) A. Dy2TiO5 was also fabricated as a bulk, single-phase compound with hexagonal symmetry, P63/mmc space group, with cell parameters a = b = 3.6307(2), c = 11.8963(8) A. The radiation response for each of the polymorphs has been investigated in-situ via 1 MeV Kr – ion-irradiation and transmission electron microscopy characterisation at the IVEM-TANDEM facility, Argonne National Laboratory. Critical temperatures, Tc, for maintaining crystallinity during irradiation were determined and showed Dy2TiO5 with either orthorhombic or cubic symmetry to perform the best, with the lowest Tc values of 711 and 761 K respectively when compared with the hexagonal form. These relatively low Tc values may be attributed to different characteristics for each phase; high anti-site defect formation energy for the orthorhombic symmetry, and the ability to accommodate disorder for the cubic symmetry.