Ion Transport Through Duplex Amorphous/Crystalline Barrier Aluminum Oxide Films

Amorphous anodic was deposited on an Al substrate that was previously coated with crystalline anodic (γ'‐alumina structure). Total 16O and 18O concentrations were measured and the 18O depth profile was determined using nuclear microanalysis techniques. It was found that oxygen transport does not occur by a simple conservation of order mechanism, but more data are needed before an alternate mechanism can be proposed. The oxygen transport number is smaller than during growth of pure amorphous oxide (0.34 vs. 0.59). Unusual aspects of amorphous deposition onto γ'‐alumina are high electronic conductivity and growth of a porous non‐barrier layer.