Microstructure change and deuterium permeation behavior of the yttrium oxide coating prepared by MOCVD

Deuterium permeation measurements and microstructure analysis on yttrium oxide coating deposited by metal organic chemical vapor deposition (MOCVD) were studied. The composition and microstructure of the coating can be adjusted by tuning sublimation temperature and deposition temperature. It is found that the coating sublimated at 150 °C and deposited at 600 °C possesses compact surface morphology with no pinholes or cracking was observed. Moreover, the oxygen/yttrium ratio corresponding well to the stoichiometric Y₂O₃ was observed by X-ray photoelectron spectroscopy (XPS) with no moving of Y3d binding energy doublet peaks and O1s binding energy peak at different depth throughout the coating. The permeation properties of coatings depended much on the microstructure. The coating sublimated at 150 °C and deposited at 600 °C exhibits the best permeability property with PRF values 412–244 at 873–973 K. However, a permeability drop, especially for the 800 °C deposited coating was observed. It was believed that the obvious increase of pinhole and crack density caused the increase of deuterium permeability. Furthermore, the existence of (Fe,Cr)₂O₃, forming a grid structure in the natural oxide layer of stainless steel, increases its hydrogen permeability.