Phase transformations induced by heavy ion irradiation in Gd_2O_3: Comparison between ballistic and electronic excitation regimes

摘要

The structural transformations induced in cubic (C-type) Gd2O3 irradiated with low-energy (4 MeV Au, ballistic regime) or high-energy (similar to 100 MeV Pb or Xe, electronic excitation regime) ions have been studied via the combination of X-ray diffraction (XRD) and Raman spectroscopy. Results show that Gd2O3 undergoes a monoclinic (B-type) phase transformation in both ion irradiation regimes. Nevertheless, significant differences are observed: (i) with low-energy ions the B-type polymorph seems to be produced by direct impact, whereas in electronic excitation regime it is formed via a complex phase transformation buildup; (ii) the B-type structure produced by low-energy ions is different from that induced by swift heavy ions. In the latter case the relative intensities of XRD peaks differ significantly from those found for a B-type reference. This effect is not due to the formation of a preferential crystalline orientation but likely to slight deviations of internal cell parameters of the B-phase formed by high-energy ion irradiations. Thus, electronic excitation produces a "pseudo" B-type poly morph. Finally, it is worth noting that the B-type phase induced by 92 MeV Xe ion irradiation remains stable up to a temperature of 900 degrees C.