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Highlights: [•] Li–Pb compatibility of Er2O3 and Er2O3-Fe two-layer coatings was examined with static immersion tests. [•] Li–Pb corrosion occurred at the Er2O3 coating surface with loss of Er, and the coating–substrate interface. [•] Deuterium permeation reduction of Er2O3 coatings after Li-Pb compatibility tests at 500°C severely degraded after 1505-h immersion. [•] Fe outer layer decreased corrosion rate of Er2O3 coatings, but was corroded at 500°C. [ABSTRACT FROM AUTHOR]

Abstract: To mitigate magnetohydrodynamic (MHD) pressure drop in liquid Li blanket system, Er2O3 coating is under development. Er can oxide in Li and form Er2O3 layer which may have electrical insulating capacity. To investigate formation of Er2O3 layer on Er, immersion tests of Er plate into high temperature Li at 773K and 973K are carried out. Li2O was introduced into Li as O agent. Formation of Er2O3 layer was observed by SEM observation and XRD analysis. Formation rate became lower for long-term immersion. Formation of LiErO2 was negligible even for high O concentration condition. From these results, there is possibility that Er can form Er2O3 insulating layer on the surface. [Copyright &y& Elsevier]

Abstract: Corrosion of Er2O3 coatings in liquid Li is crucial issue for Li blanket system development. Recent researches revealed that the Er2O3 forms LiErO2 in Li and the reaction rate depends on the O concentration in Li. In this paper, the detailed chemical behavior of Er2O3 and LiErO2 in Li is investigated to develop a methods to prevent the corrosion of Er2O3. Test of Er2O3 bulk ceramics were carried out with several impurity and Li flow condition. From these corrosion tests, it became clear that LiErO2 is not stable in low O concentration Li, but corrosion can be prevented by O concentration control. Corrosion prevention was tested in flowing Li and it suggests Er2O3 can be stable in Li with O control, even with flow, or thermal gradient condition. [Copyright &y& Elsevier]

• The properties of isolated O vacancies of Er 2 O 3 were investigated by DFT method. • The defect formation energy of H-related vacancy decreases in the charged environment. • H 1 s orbital forms multicenter bonds with the 5 d orbital of the NNN Er atoms. • The net charge transfer from the defected Er 2 O 3 to the H atom is derived. Point defects created by neutron/electron irradiation often determine the performance and the chemical stability and activity of oxide materials. Oxygen vacancies constitute a common point defect in metal oxides, such as erbium oxide (Er 2 O 3), one of the candidate materials for tritium permeation barriers in fusion blanket systems. However, a systematic study of the oxygen vacancy properties in Er 2 O 3 has been lacking. Here, the properties of isolated neutral and charged oxygen vacancies in Er 2 O 3 are investigated by means of supercell total-energy calculations using a first-principles method based on density–functional theory. Vacancy formation energies, hydrogen–vacancy interactions, and geometry rearrangements around these point defects are investigated in detail. The characterization of the electronic structure of these point defects is established by the analysis of the spin-orbital density of states. It is found that the energetic and electronic properties of the oxygen vacancies depend on the chemical potentials of the O and Er atoms in Er 2 O 3. The defect formation energy decreases when one hydrogen atom is trapped into the vacancy in both charged oxidizing and reduced environments. Also, the interstitial hydrogen 1 s orbital forms multicenter bonds with the 5 d orbital of the neighboring Er atoms, and the net charge transfer from the defected Er 2 O 3 is 1.04e, 1.02e, and 0.80e for the defect charge states of 1−, 0 and 1+, respectively. We suggest that the H-decorated vacancy defect may be responsible for the increase of the self-healing properties of Er 2 O 3. [ABSTRACT FROM AUTHOR]

Erbium oxide has been investigated as a tritium permeation barrier material in a D-T fusion reactor fuel system for more than a decade. Erbium oxide normally forms the cubic phase; however, the uncommon monoclinic phase was formed under ion irradiation or high pressure conditions. In this study, the monoclinic erbium oxide coatings were prepared to examine their microstructure and deuterium permeability with ion-irradiation effect. The monoclinic phase coatings with a preferred orientation showed 1–2 orders of magnitude higher permeability at 300–400 °C than the cubic phase coating reported previously due to the smaller grain with uncrystallized region. After the permeation measurement at 600 °C, the permeability drastically decreased due to the phase transformation to the cubic phase and a change in grain structure from columnar to granular. An Fe-ion irradiated coating with the damage concentration of 0.05 dpa showed the decrease in the permeability at 500 °C, indicating the irradiation damage to the grain structure may accelerate the grain growth at lower temperature, while the phase transformation would occur at 600 °C because the diffusivity did not change much at 500 °C and drastically decreased at 600 °C. [ABSTRACT FROM AUTHOR]

In this study, we report results using first-principles density functional theory calculations for four critical aspects of the interaction: H adsorption on Er 2 O 3 surface, surface-to-subsurface penetration of H into Er 2 O 3 , bulk diffusion of H in Er 2 O 3 , and trapping of H at vacancies. We identify surface stable adsorption positions and find that H prefers to transfer electrons to the surfaces and form covalent bonds with the nearest neighboring four oxygen atoms. For low surface coverage of H as in our case (0.89 × 10 14 H/cm 2 ), a penetration energy of at least 1.60 eV is required for cubic Er 2 O 3 surfaces. Further, the H diffusion barrier between the planes defined by Er 2 O 3 units along the favorable 〈1 1 1〉 direction is found to be very small – 0.16 eV – whereas higher barriers of 0.41 eV and 1.64 eV are required for diffusion across the planes, somewhat higher than the diffusion energy barrier of 0.20 eV observed experimentally at 873 K. In addition, we predict that interstitial H is exothermically trapped when it approaches a vacancy with the vacancy defect behaving as an electron trap since the H-vacancy defect is found to be more stable than the intrinsic defect. [ABSTRACT FROM AUTHOR]

Abstract: Deuterium permeation measurements and microstructure analyses on erbium oxide coating deposited by filtered arc deposition have been investigated. It is found that the permeation suppression efficiency is proportional to the coating thickness in case of the coating without pores and cracks reaching to the substrate. A phase transformation of the coating during the permeation measurements at 773–973K has been identified. A grain growth of the coating has occurred during the measurements and permeation suppression efficiency have enhanced according to the grain size. It is suggested that deuterium permeation through the coating is mainly dominated by the crystal grain diffusion. [Copyright &y& Elsevier]

Abstract: The development of a tritium permeation barrier is essential for building a tritium recovery system in fusion power plants. Toward realizing this application, the fabrication of erbium oxide coatings by metal-organic decomposition has been carried out on reduced activation ferritic/martensitic steels. The coated samples exhibit different surface structures after they are heat-treated under different conditions. A sample that is heat-treated in high-purity argon produces an oxide layer between the erbium oxide coating and the substrate. It is believed that the presence of this oxide layer causes defects in the coating and degradation of the samples during deuterium permeation measurements. The sample heat-treated in high-purity hydrogen with moisture exhibits a thinner oxide layer and improved stability during measurements. A 0.3-μm-thick coating yields a permeation reduction factor of 500–700 at 773–973K, which is comparable to the coating deposited by the physical vapor deposition technique. [ABSTRACT FROM AUTHOR]

Abstract: Tritium permeation barrier is required in fusion blanket for reduction of loss of fuel and health hazard. In this study, deuterium permeation experiments have been performed on four kinds of steels and erbium oxide coatings fabricated by a filtered arc deposition method. The permeation flux of uncoated samples shows diffusion-limited regime in the temperature range 573–723K and the permeability is corresponding to literature data. The coated samples deposited at room temperature have been tested at 773K. It is found that the coatings suppress the deuterium permeation to a close level in spite of different types of steel substrates. In addition, the exponent of the driving pressure slightly changes compared to the uncoated sample. However, the permeation regime is still near diffusion limited. [Copyright &y& Elsevier]

Erbium oxide (Er 2 O 3) is a candidate material for tritium permeation barriers (TPB) applied to fusion blanket systems. To permeate through a TPB coating on a metal substrate, a hydrogen isotope must first adsorb on the surface, and then penetrate from the surface into the interior. In this work, Er 2 O 3 coatings were fabricated by arc source assisted deposition and annealing at 973 K in vacuum (<10−5 Pa). The effect of hydrogen on the crystal orientation change of Er 2 O 3 coatings was examined by X-ray diffraction and density-functional theory studies. It was found that the surface energy of a partially H-covered initially {111} Er 2 O 3 slab increases upon annealing at 973 K, and that the associated crystal orientation change from {111} to {100} never occurs without hydrogen e ven at high temperature. • Surface energy of Er 2 O 3 coatings is estimated by ab initio molecular dynamics. • H plays an essential role in Er 2 O 3 surface phase transition from {111} to {100}. • The mechanism of Er 2 O 3 crystal orientation change is elucidated. [ABSTRACT FROM AUTHOR]

Abstract: Deuterium permeation through Er2O3-metal coatings showed that the metal layers had small effects on the permeation behavior. The Er2O3–Fe coating increased permeation reduction factor to over 103 by crystallization of the inner Er2O3 layer and oxidation of the outer Fe layer. In the Er2O3–Er coating, the Er layer oxidized completely and merged with the inner Er2O3 layer during permeation, resulting in a permeation reduction factor similar to that of single Er2O3 layer. These results prove the applicability of multilayer structures for a tritium permeation barrier. Moreover, optimizing coating material structures will enhance compatibility with blanket structures and further reduce permeation. [Copyright &y& Elsevier]