Microcrystallinity in ‘X-ray amorphous’ anodic Ta2O5

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Abstract
Microdiffraction has been employed to obtain further insight into the structure of ‘X-ray amorphous’ anodic Ta2O5. Microdiffraction, allied with the specimen preparation technique of ultramicrotomy, enables the diffraction patterns to be extracted from exceedingly small volumes, about 1000 nm3, of film material. Diffraction patterns extracted from such fine volumes reveal clearly the structural inhomogeneities in the ‘X-ray amorphous’ anodic Ta2O5. It was found, for the first time, that the anodic Ta2O5 is not entirely amorphous or microscopically uniform in structure but appears to contain microcrystalline regions which are too fine to be detected by conventional X-ray or electron diffraction, even without annealing at elevated temperatures. Implications for the relationship between the structural inhomogeneities and ionic transport processes are discussed.