Ion beam induced reduction of metallic cations in yttria-zirconia

Samples consisting in polycrystalline films of 8 wt.% Y2O3-ZrO2, 0.8 mm thick, deposited by plasma spray technique, were irradiated with 1-4 keV Ar ions in the fluence range between 1 x 10(16) and 7 x 10(17) ions/cm(2). The formation of radiation-induced Zr(III) and Zr(II) as well as Y(II) suboxides is demonstrated by using X-ray photoelectron spectroscopy (XPS). In particular, reduced species start to be observed when the energy of the irradiating ions is higher than 1 keV, while the relative amount of the low valence cations produced for a given fluence in the altered layer has been found to depend on the primary ion energy. The results obtained by angular dependent XPS (ADXPS) analysis suggest that the in-depth distribution of the Zr and Y reduced species also depends on the primary ion energy, In particular, for samples irradiated with 2 keV Ar ions the Zr (and Y) reduced species are detected at the surface, while for samples irradiated with 4 keV ions the reduced species are found to be mostly localized in depth. The observed irradiation effects are explained in terms of bombardment-induced Gibbsian segregation (BIS) mechanism.