Complete phase transformation in zirconia induced by very high electronic excitations

It is now well established that the irradiation of pure zirconia (ZrO₂) with swift heavy ions can lead to a transformation from the monoclinic to the tetragonal phase when the deposited electronic energy loss exceeds an effective threshold ∼12 keV nm⁻¹. Previous swift heavy ion irradiations carried out with electronic energy losses less than ∼30 keV nm⁻¹ evidenced that this phase transition is characterized by two constant features: (i) it is driven by a double ion impact process, and (ii) it is never complete even at extremely high fluences. It is then quite interesting to check whether this phase transformation does not depart from this behaviour at very high electronic energy losses. For this purpose, zirconia was irradiated with 0.6-GeV Pb ions giving rise to an electronic energy loss ∼42 keV nm⁻¹ at the sample surface. Despite this huge value, the experimental data revealed that the phase change is here again still characterized by a double ion impact process. However, contrary to previous cases, it was found that this phase transformation not only occurs very rapidly but achieves full completion at rather low fluences.