XPS investigation of impurity phase segregation in 25.5 wt.% CeO2-2.5 Y2O3-72 ZrO2 plasma-sprayed thermal barrier coatings

X-ray photoelectron spectroscopy (XPS), angular-dependent XPS and x-ray-induced Auger electron spectroscopy (XAES) have been used to investigate impurity (Si, Na and Al) segregation in 25.5 wt.% CeO2-2.5 Y2O3-72 ZrO2 plasma-sprayed thermal barrier coatings (TBCs) as a function of high-temperature air thermal treatment (up to 1460°C). The segregated phase, present in a similar composition both on the as-thermally treated and fracture surfaces, forms a thin layer of approximately 20 nm thick. This phase contains both silicon and sodium at a temperature ranging between 900 and 1350°C and it is also enriched with aluminium at higher temperatures. The XPS and XAES results are used to identify the chemical composition of this surface phase.