“…An ideal TGO should be slow growing, continuous, and adherent to BC. As ␣-Al 2 O 3 has extremely low self and impurity diffusion rates, and its chemical and thermal stability is relatively high, ␣-Al 2 O 3 is preferred to other oxides such as NiO, Cr 2 O 3 , Ni(Al,Cr) 2 O 4 , and -Al 2 O 3 [4][5][6][7]. To form and maintain the growth of ␣-Al 2 O 3 scale at high temperatures, a high Al content is demanded for a good BC.…”