2D-HARECXS analysis of dopant and oxygen vacancy sites in Al-doped yttrium titanate

A Y2Ti2O7/Al2O3 multilayer, exhibiting high thermal reflectivity and oxidation resistivity, holds potential as a functional surface coating for advanced gas turbine blades. Slight Al doping of Y2Ti2O7 has been found to significantly improve the structural stability of the multilayer, the detailed mechanism of which remains unclear. Hence, we examined the site occupancies of doped Al using high-angular resolution electron channeling X-ray spectroscopy with two-dimensional rocking of the incident electron beam. A statistical linear regression analysis of a set of observed ionization channeling patterns (ICPs) of fluorescent X-rays quantitatively confirmed that Al3+ preferentially occupied the Ti4+ site, rather than the Y3+ site, because of the large difference in the ionic radii of Al3+ and Y3+. Furthermore, the comparison of theoretical and experimental X-ray ICPs showed that oxygen vacancies V-O were introduced at the 48f site, the first-nearest neighbor of the Ti site, which was consistent with the hypothesis that oxygen vacancies compensate for the local charge imbalance associated with preferential substitution of Al3+ for Ti4+. Our findings can aid in improving the thermal properties of environmental barrier coatings applied to advanced jet engines and also demonstrate the utility of beam-rocking schemes for investigating dopant effects in various functional materials.