XPS-SIMS studies of impurities phase segregation in 25.5 wt% CeO2 - 2.5 Y2O3 - 72 ZrO2

X-ray photoelectron spectroscopy (XPS), X-ray induced Auger electron spectroscopy (XAES) and secondary ion mass spectrometry (SIMS) have been used to investigate segregation phenomena at fracture surfaces of thermal treated (up to 1460_C) 25.5 (wt%) CeO2-2.5 Y2O3-72 ZrO2 plasma sprayed thermal barrier coatings (TBC). The results show that segregation of bulk dissolved impurities and of yttrium stabilizing oxide, takes place at the fracture surfaces starting from 900_C. The chemical nature of the segregated phase is ascribable to an infinite chain silicate of sodium and yttrium with the presence of aluminium and iron at temperature equal to and higher than 1100_C. SIMS ion images show further that aluminium segregates both at the silicate segregated regions as well as separately. The effect of these segregation phenomena on the properties of the TBC's is discussed.