Microstructural Features in Aged Erbium Tritide Films

Aged erbium tritide foil specimens are found to contain five distinctly different microstructural features. The general structure was of large columnar grains of ErT2. But on a fine scale, precipitates believed to be erbium oxy-tritides and helium bubbles could be identified. The precipitate size was in the range of ~10 nm and the bubbles were of an unusual planar shape on {111} planes with an invariant thickness of ~1 nm and a diameter on the order of 10 nm. Also, an outer layer containing no fine precipitate structure and only a few helium bubbles was present on foils. This layer is best described as a denuded zone which probably grew during aging in air. Finally, large embedded Er2O3 particles were found at low density and non-uniformly distributed, but sometimes extending through the thickness of the foil. A failure mechanism allowing the helium to escape is suggested by observed cracking between bubbles closer to end of life.