采用PBE形式的广义梯度近似(GGA)的第一性原理计算方法研究了氢或氦在钨中产生点缺陷的形成能以及缺陷形成后对钨的弹性的影响;采用同样的方法研究了空位和自间隙原子这两种缺陷.经计算发现:氢氦掺杂在钨的晶体结构中会引起晶体体积的变化,其变化结果跟掺杂的位置有关,在四面体或八面体处的掺杂会使晶体体积增加,替位掺杂会引起晶体体积减小;从形成能来看,氢掺杂在钨中最占优的位置是四面体处,而氦最占优的则是替位掺杂.在几种缺陷中,形成能最小的是氢的四面体掺杂,形成能最大的则是钨的自间隙原子形成;钨中若含有氢或氦的点缺陷,晶体的体弹模量和剪切模量会发生改变,当钨中含有氢替位或自间隙原子时晶体会向塑性改变,含有其他点缺陷时晶体会沿着脆性方向转变.但总体来说带有缺陷的钨仍然具有延展性.值得注意的是,氢或氦在钨中会引起晶体的各向异性,其具体结果与缺陷所处位置相关,只有缺陷属于替位时才不会发生各向异性.本文的研究工作可为第一壁材料的开发提供理论参考.%The formation energy of all kinds of point defects formed by hydrogen or helium and the change of elastic constants of tungsten containing a point defect were studied by using first-principles method based on GGA with a PBE form.The other two kinds of point defects,such as vacancy and self interstitial atom in tungsten,were studied by using the same method.After calculation,we found that the crystal volume has some changes due to the formation of a point defect in the tungsten formed by hydrogen or helium.And the results depend on the sites of point defects.The crystal volume becomes bigger when the defects are located in the tetrahedron or octahedron sites,while the volume becomes smaller when a tungsten atom is replaced by a hydrogen or helium atom.For helium,the substitu-tion site is the most favorable over the tetrahedron and octahedron sites.For hydrogen,on the contrary,the tetrahedron site is the most perfect site over the substitution and octahed-ron sites.In these defects,we can find the smallest formation energy corresponds to the defect formed hydrogen which located in tetrahedron site,and the biggest formation energy to the formation of a self interstitial atom.If tungsten contains a point defect formed by hydrogen or helium,the body modulus and the shear modulus will have some changes.The crystal will change to plastic when there is a hydrogen substitute defect or self interstitial atom in tungsten.The tungsten becomes more brittle when it contains other point defects, but it still has the ductility in total.The crystals may become anisotropy when there is a defect in tungsten,and the results depend on the site of the defects.Only for the defects at the substitute site,the anisotropy will not happen.The research can provide a theoretical reference for the development of the plasma facing materials.
展开▼
