Fe effect on hydrogen interactions with intrinsic point defects and hydrogen migration in α-Al2O3 based tritium permeation barriers

The Role of Carbon in the Formation of Intrinsic Point Defects and Hydrogen Migration in α‐Al2O3‐Based Tritium Permeation Barriers

“…[12] Moreover, in the entire energy-level range in C-doped α-Al 2 O 3 , the relative proportion of H i þ is significantly smaller than that of H i À , consistent with the case in Cr-doped α-Al 2 O 3 ; [11] while in pure α-Al 2 O 3 , the ratio of H i þ /H i À is slightly greater than 1, [11] yet the ratio in Fe-doped α-Al 2 O 3 is slightly smaller than 1. [12] Obviously, the introduction of C has some influence on the electron-phonon interactions in α-Al 2 O 3 , and the influence extent is different from the cases of Fe and Cr doping, showing the different influence of composition on the material property. On the other hand, after C doping, the formation energy of H i in α-Al 2 O 3 within the entire energy-level range is less than zero, indicating that it can be thermodynamically stable in the material and formed spontaneously; while in undoped and Fe-, Cr-doped α-Al 2 O 3 , [11,12] the formation energy of H i in certain energy-level range is positive.…”

“…The reduction of H i formation energy can also be observed in Fe-and Cr-doped α-Al 2 O 3 . [11,12] It can thus be seen that the formation and existence of H i in α-Al 2 O 3 will be greatly affected by C.…”

“…The case resembles that in Fe-or Cr-doped α-Al 2 O 3 , but the proportion of the neutral state in the former is smaller than that in the latter two. [11,12] Moreover, the proportion of the negative charged [V O -H] in α-Al 2 O 3 after C doping is twice that of the positive charged state, while the ratio of…”

“…[6,7] For example, transition metal impurities Fe and Cr have important effects on the color, defect process, phase transition, surface electronic structure, and hydrogen behavior such as adsorption, dissociation, and migration of α-Al 2 O 3 . [8][9][10][11][12][13] Carbon is also a common impurity element in α-Al 2 O 3 , originating from any steps in the technologic processing, such as doping in the synthesis or manufacturing process, trace carbon-containing atmosphere in the sintering process, residual organic matters in the cleaning or synthesis process, and even mechanical treatment such as machining, polishing, etc. [14] It is found that the type, distribution, and content of carbon source play an important role in the microstructure evolution of Al 2 O 3 -C refractories.…”

“…For α-Al 2 O 3 -based TPBs, the impurity effect in hydrogen transport behaviors is one of the major concerns because it is directly related to the hydrogen permeation resistance of the coating, and the selection and optimization of the coating preparation technology. [11][12][13] Our previous theoretical studies [11,12] pointed out that both the transition metal elements Fe and Cr have important effect on hydrogen interactions with intrinsic point defects and hydrogen migration behaviors in α-Al 2 O 3 , but their influence extent and specific role are different. Jiang et al [13] found that Fe will reduce the activation energy of hydrogen atom recombination on the α-Al 2 O 3 (0001) surface, although Fe has little effect on the adsorption and diffusion of H 2 molecules on the same surface.…”