S. Moll

Phase transformations induced by high electronic excitation in ion-irradiated Gd2(ZrxTi1−x)2O7 pyrochlores

The pyrochlore oxides (A2B2O7) exhibit a remarkable range of structural, physical, and magnetic properties related to their various chemical compositions. This article reports the phase transformations induced by high electronic excitation in pyrochlores of the Gd2(ZrxTi1−x)2O7 family irradiated with swift ions. The structural changes, investigated by using several analytical techniques (x-ray diffraction, Raman spectroscopy, and transmission electron microscopy), strongly depend on the chemical composition. The high electronic excitation along the ion trajectory results in the amorphization of ion tracks for Gd2Ti2O7 and Gd2TiZrO7, whereas a defective fluorite structure is formed in Gd2Zr2O7. Moreover, the results underline the existence of an electronic stopping power threshold of 6 keV/nm for amorphizable compounds and 10 keV/nm for Gd2Zr2O7, below which phase transformations do not occur. Finally, the study of the thermal recovery of irradiated pyrochlores provides the recrystallization temperature fo...

Damage induced by electronic excitation in ion-irradiated yttria-stabilized zirconia

This article presents a study of the damage production in yttria-stabilized cubic zirconia single crystals irradiated with swift heavy ions. The combination of techniques which probe the material at different spatial scales (Rutherford backscattering spectrometry in channeling geometry, x-ray diffraction, transmission electron microscopy, and atomic force microscopy) was used in order to gain information about the damage depth distribution, the disordering buildup, the nature of radiation defects, and the occurrence of microstructural modifications. The damage results from the formation of tracks, due to the huge electronic excitations induced in the wake of incident ions. The melting of the material in the core of tracks, via a thermal spike mechanism, leads to the creation of large hillocks at the surface of the crystals. The overlapping of ion tracks at high fluence (above similar to 10(12) cm(-2)) induces a severe transformation of the microstructure of the material. Nanodomains slightly disoriented from the main crystallographic direction are formed, with a size decreasing with increasing irradiation fluence. These results may be used to predict the damage evolution in other nonamorphizable ceramics irradiated with swift heavy ions.

Radiation Resistance of Fluorite‐Structured Nuclear Oxides

Fluorite‐structure oxides are radiation‐resistant materials making them ideal candidates for uses as nuclear fuels or as inert matrices for actinide transmutation. The radiation tolerance of urania and cubic zirconia single crystals was investigated by external ion irradiation in predominating domains of electronic and nuclear stopping of bombarding particles. Damage kinetics show that the behavior of the two investigated fluorite‐type oxides is almost the same: (i) at low‐energy a two‐stage disordering process is exhibited—first a ballistic step due to the formation of radiation‐induced defects and second a crystal fragmentation induced by the formation of gas bubbles at large concentration‐; (ii) at high energy a one‐stage damage kinetics associated with the formation of ion tracks whose overlapping at high fluence results in the formation of nanometer‐sized domains with a small disorientation.