Ge、Si元素对ZrO_2和Zr(Fe,Cr)_2能量与电子结构的影响

Effects of Ge,Si Addition on Energy and Electronic Structure of ZrO_2 and Zr(Fe,Cr)_2

采用基于密度泛函理论的第一性原理计算方法,研究Ge、Si元素对锆合金中与腐蚀相关的ZrO_2氧化膜相和Zr(Fe,Cr)_2第二相能量与电子结构的影响。合金形成热、结合能的计算结果表明:ZrO_2四方相结构不稳定,立方相易形成且结构稳定,氧化膜晶体结构从四方相向立方相发生转变影响锆合金的耐腐蚀性能;Ge、Si元素均降低ZrO_2立方相的结构稳定性和形成能力,与Ge相比,Si易取代Zr(Fe,Cr)_2第二相中的Cr,增加锆合金Fe/Cr原子比。电子态密度和Mulliken电子占据数的计算结果表明:ZrO_2中Zr与O存在杂化共振与较强的离子键作用,Ge、Si降低ZrO_2立方相结构稳定性的原因主要在于削弱了Zr-O之间的离子键作用;ZrO_2氧化膜相和Zr(Fe,Cr)_2第二相是影响锆合金耐腐蚀性能的两个重要因素,对Si而言,形成含Si的Zr(Fe,Cr)_2第二相对锆合金耐腐蚀性能产生不利影响,改善锆合金耐腐蚀性能需要ZrO_2晶体结构改变占主导地位;对Ge而言,含Ge的Zr(Fe,Cr)_2第二相难形成,第二相对锆合金耐腐蚀性能的影响相对Si较小,减缓ZrO_2由四方相向立方相的转变倾向,是Ge改善锆合金耐腐蚀性能的重要原因。

Effects of Ge,Si addition on energy and electronic structure of ZrO_2 and Zr（Fe,Cr）_2 related to the corrosion of zirconium alloy were studied by First-principles calculations based on the density functional theory.The calculated heats of formation and cohesive energies show that ZrO_2 tetragonal phase is not stable,cubic phase is easily formed and has the highest structural stability,thus the change occurs from tetragonal phase to cubic phase for crystal structure of oxidation,which affects the corrosion resistance of zirconium alloy.Ge,Si can reduce the forming ability and structural stability of ZrO_2 cubic phase,Si can easily replace Cr atoms of Zr（Fe,Cr）_2 systems,thus Fe/Cr atomic ratio of the second phase in zirconium alloy is improved.The calculations of the density of states（DOS）and Mulliken electronic populations show that hybrid resonant phenomenon and more ionic bonds are both seen between Zr and O of ZrO_2,and the reason of reduced structural stability of ZrO_2 cubic phase attributes to the weakened ionic bonds between Zr and O with the addition of Ge,Si.It is considered as ZrO_2 and Zr（Fe,Cr）_2 phase for affecting the corrosion resistance of zirconium alloy.In the case of adding Si,Si contained second phase Zr（Fe,Cr）_2 is harmful to corrosion resistance of zirconium alloy,if the change of ZrO_2 crystal structure is dominated,the corrosion resistance of zirconium alloy will be improved.As far as Ge is concerned,it is difficult for the formation of Ge contained second phase Zr（Fe,Cr）_2,thus the influence of second phase on corrosion resistance of zirconium alloy is less than that of adding Si.If the change tendency from tetragonal phase to cubic phase has slowed down,the corrosion resistance of zirconium alloy will be improved.