10 MeV Au ion irradiation effects in an MgO-HfO2 ceramic-ceramic (CERCER) composite

Room temperature ion irradiation damage studies were performed on a ceramic composite intended to emulate a dispersion nuclear fuel. The composite is composed of 90-mole% MgO and 10-mole% HfO2. The as-synthesized composite was found to consist of Mg2Hf5O12 (and some residual HfO2) particles embedded in an MgO matrix. X-ray diffraction revealed that nearly all of the initial HfO2 reacted with some MgO to form Mg2Hf5O12. Ion irradiations were performed using 10 MeV Au3+ ions at room temperature over a fluence range of 5 x 1016-5 x 1020 Au/m2. Irradiated samples were characterized using both grazing incidence X-ray diffraction (GIXRD) and transmission electron microscopy (TEM), the latter using both selected-area electron diffraction (SAED) and micro-diffraction (μD) on samples prepared in cross-sectional geometry. Both GIXRD and TEM electron diffraction measurements on a specimen irradiated to a fluence of 5 x 1020 Au/cm2, revealed that the initial rhombohedral Mg2Hf5O12 phase was transformed into a cubic-Mg2Hf5O12 phase. Finally, it is important to note that at the highest ion fluence used in this investigation (5 x 1020 Au/m2), both the MgO matrix and the Mg2Hf5O12 second phase remained crystalline.