Surface stability and H adsorption and diffusion near surfaces of W borides: a first-principles study

Nuclear Fushion

article

L. Yang¹  B.D. Wirth¹ 

[1] Department of Nuclear Engineering, University of Tennessee;Fusion Energy Division, Oak Ridge National Laboratory

关键词: tungsten boride surface;    hydrogen;    adsorption;    diffusion;    DFT calculation;   

DOI  :  10.1088/1741-4326/acc6de

来源: Institute of Physics Publishing Ltd.

【 摘 要 】

Understanding the behavior of tungsten boride (W _x B _y ) surfaces in a fusion reactor environment is an important topic since boronization is a common wall conditioning method used in fusion Tokamaks. We report the results of density functional theory calculations that investigate the surface stability of W _x B _y(tetragonalI4₁/amd -WB, hexagonalP 6₃/ mmc -WB₂ and tetragonalI4/m- W₂B) with low-index orientations, as well as hydrogen (H) energetics near W _x B _ysurfaces. For single element terminated W _x B _ysurfaces, B terminated surfaces are more energetically stable than W terminated as a result of significant reconstruction of B. The H surface adsorption energy and activation energy of H diffusion penetration below W _x B _ysurfaces are mainly related to the outer termination. Specifically, the WB(001) surface terminated with two B layers, referred to as WB(001)-T_BB, has higher H adsorption affinity and lower H diffusivity on this surface than other terminations, which is controlled by the significant charge transfer from B to H. However, B atoms on the WB₂(0001)-T_BB surface decrease both H adsorption and diffusivity on the surface, but enhance H diffusion below the surface in comparison to W terminated WB₂(0001) surface. H would be trapped and diffuse within atomic surface gaps on the WB₂(2bar 1bar 10 ) surface, while H below the surface layer would jump along the [0001] direction rather than diffuse into bulk. The surface diffusion activation energy of H on the W₂B(001) surface slightly varies with terminations. Once H crosses the surface layer of W₂B(001) with either termination, it prefers to diffuse into the bulk, or back towards the surface, rather than move parallel to the surface. Interestingly, WB₂(0001) and WB₂(2bar 1bar 10 ) surfaces will have relatively higher H retention than the other W _x B _ysurfaces evaluated in this work.

【 授权许可】

Unknown