Hydrogen Behavior In W-doped α-Al₂O₃ Tritium Permeation Barrier Material Via First Principle Approach

In future fusion reactors,the amount of tritium handled between the vacuum chamber and the fuel cycle system will reach several kilograms per hour,more than any existing tritium facility in the world.One of the technical challenges of handling such large amounts of tritium is effectively limiting tritium in containers and pipes.Tritium,the fuel for fusion,has small atoms that migrate easily,causing three major problems:material embrittlement,fuel leakage and radioactive contamination of the environment.Therefore,preventing tritium permeation is an important research topic of fusion reactor.In order to solve the above problems,in addition to the design of tritium containment structure,another effective measure can be taken is to coat the tritium related parts in the fusion reactor with special materials of corresponding thickness to reduce tritium penetration,α-Al₂O₃ has become one of the most mainstream tritium-resistant coatings due to its high tritium-resistant factor and good comprehensive performance.At present,plasma-facing materials in fusion reactor devices are container walls that directly contain plasma and directly contact with plasma,including the first wall and deflector.At present,the most suitable material type for this part is metal tungsten（W）,because tungsten（W）material has the characteristics of high temperature resistance,almost no reaction with H,low sputtering rate,and low H retention rate,ITER has established an all-W design route.In view of the development trend of facing plasma materials,tungsten（W）may be widely used in fusion device,so it is necessary to study the tritium-resistant materials coated on the tungsten wall.However,we have not found any research on tritium-resistant coating on tungsten surface and influence of tungsten doping on the performance of tritium-resistant materials.Based on the first-principles studies of density functional theory,the behavior and related mechanisms of hydrogen in W dopedα-Al₂O₃ tritium-resistance materials can be understood at the atomic level,which is of great significance for solving the problem of unclear microscopic mechanism of tritium resistance and further designing a tritium resistance coating with stronger tritium resistance effect.·The main contents are as follows:（1）Determine the stable configuration of W-dopedα-Al₂O₃（0001）surface,obtain the most stable doping position of tungsten（W）on theα-Al₂O₃（0001）surface,and determine the stable structure of tungsten dopedα-Al₂O₃ type.（2）The adsorption and dissociation behaviors of hydrogen on the surface of W-dopedα-Al₂O₃（0001）were studied.The adsorption behavior of hydrogen molecules and hydrogen atoms on the surface of W-dopedα-Al₂O₃（0001）was studied respectively,and the stable and secondary adsorption sites of hydrogen molecules and hydrogen atoms on the surface of W-dopedα-Al₂O₃（0001）were determined.By comparing the hydrogen adsorption behavior on pureα-Al₂O₃（0001）surface,the effect of W doping on the hydrogen adsorption and dissociation onα-Al₂O₃（0001）surface was determined.（3）The transition state search method was used to study the migration process of hydrogen on the W-dopedα-Al₂O₃（0001）surface and the pureα-Al₂O₃（0001）surface.By comparing the migration paths and potential barriers of the two systems,the effect of W doping on the The effect of hydrogen diffusion at the surface and from the surface to the subsurface.（4）The existence form and diffusion behavior of hydrogen in the W-dopedα-α-Al₂O₃bulk phase and the pureα-Al₂O₃ bulk phase were compared and analyzed,and it was determined that the existence of tungsten impurities had an influence on the existence of hydrogen in theα-Al₂O₃ bulk phase and the relationship between hydrogen and this.The effect of point defect interactions.The main research methods of this subject are based on the first-principles calculations of density functional theory and the transition state search.Theoretical research determines the effect of tungsten doping on the diffusion path and the difficulty of diffusion of hydrogen isotopes in the coating material,and thus predicts the tritium resistance effect of the W-dopedα-Al₂O₃tritium resistance coating,which is theoretical exploration to improve the tritium resistance ofα-Al₂O₃ coating materials.