钚氧化层结构的理论研究进展

Progress in Theoretical Investigation on Oxide Layer Structure Over Metallic Plutonium

钚的氧化层结构是钚化学腐蚀的中心科学问题,本文回顾了本课题组最近在这方面的理论研究工作。首先,基于第一性原理计算结合化学热力学,说明单氧化钚在常压下是热力学不稳定的,可能分解成Pu_(2)O_(3)和钚,但是压强可以将单氧化钚稳定下来,电子结构计算说明了其中的稳定机制。其次,基于准随机结构的第一性原理计算,说明碳也可以将单氧化钚稳定下来。并且重现了碳氧化钚的晶格常数反常演化并阐释其微观电子结构机制。最后,基于类比镧系的过渡氧化物结构模型,预测在Pu_(2)O_(3)/PuO_(2)层中存在低对称结构的Pu_(n)O_(2 n-2)。基于这些工作,提出了一种阶梯状的氧化层结构模型(Pu/PuO_(x)C_(y)/Pu_(2)O_(3)/Pu_(n)O_(2 n-2)/PuO_(2)),以改进简单的三明治状氧化层模型。这个结构模型为钚的化学腐蚀研究提供了一定的理论指导价值。

The oxide layer structure over plutonium is the central issue of plutonium corrosion science.In this paper we review our progress in theoretical investigation on the oxide layer structure of plutonium.First of all,our first-principles calculations combined with chemical thermodynamics shows that plutonium monoxide is unstable under ambient pressure and probably decompose into plutonium sesquioxide and metallic plutonium.However,it could be stabilized under pressure and the stabilization mechanism is illustrated by the electronic structure calculations.Secondly,based on the quasirandom structure model,the first-principles calculations show that monoxide could also be stabilized by the carbon.The anomalous variation of lattice parameter of oxycarbide is reproduced by our theoretical studies and the microscopic origin is revealed.Finally,using analogous structures of lanthanide intermediate oxide,we show that homogeneous Pu_(n)O_(2 n-2)between PuO_(2)and Pu_(2)O_(3)are energetically favorable.Thus,a ladder-like layer structure(Pu/PuO_(x)C_(y)/Pu 2O 3/Pu_(n)O_(2 n-2)/PuO 2)is proposed to improve a simple sandwich-like model of the oxide layer over metallic plutonium.This model provides theoretical guidance for the research on the plutonium corrosion.