高温delta基钚合金相稳定性及磁力学性能的理论研究

Under reasonable design, the high-temperature face-centered-cubic-based plutonium alloys (high-temperature delta-based plutonium alloys) can be stabilized near room temperature and like pure aluminum, possess a good technical property. The high-temperature delta-based plutonium alloys are hoped to become one of the hotspots in the area of nuclear materials scientific research. With the variation of their composition or preparation process, the high-temperature delta-based plutonium alloys can present to be delta’ or epsilon phase, besides the delta one. The appearance of the delta’ or epsilon phase has great influence on the magnetic and thermodynamic performance of these alloys. Understanding the nature of each phase and then proper control it are the key to achieving these special high-temperature delta-based plutonium alloys, which are even stable in room temperature and possess much optimized performance. However, the delta-based plutonium alloys are highly toxic and radioactive, which provide great inconvenience for experimental measurements. In addition, this group of alloys are generally in high-temperature paramagnetic state, with atomic and magnetic disorder, and also a strong correlation between 5f electrons and spin fluctuations, which all cause great difficulties for the first-principles investigation of these alloys. Therefore, it results that Until now, the nature of each phase in the high-temperature delta-based plutonium alloys is still unclear. Using the first-principles EMTO-CPA in combination with spin dynamics UppASD methods in the project, we plan to systematically calculate the influences of both the alloying and temperature on the lattice parameter, magnetism, elastic modulus, and free energy; and then approximately determine the composition phase boundary and the phase transition temperature; explore the rules of both alloying and temperature effects on the magnetism, thermodynamic properties, and phase stability, together with their correlation and corresponding physical mechanism; and finally provide a theoretical basis for accounting for their excellent performance, and by reasonable control of alloying components, achieving these delta-based plutonium alloys which are stable in room temperature and with much optimized performance.

合理设计的面心立方钚基高温合金（delta基钚高温合金）可稳定于室温且具纯铝的良好加工性能，有望为核材料领域研究热点之一。随成分及制备工艺不同，delta基钚高温合金中除delta外，还会出现delta’和epsilon相，对其磁热力学性能有重要影响。了解各相性质并对其恰当控制，是实现delta基钚高温合金室温稳定和性能优化的关键。delta基钚合金剧毒放射性，极不便实验测量；此高温顺磁、具5f电子强相关及磁自旋波动的无序合金又为第一原理计算造成极大困难。目前人们对各相缺乏本质认识。本项目拟采用第一原理EMTO-CPA结合自旋动力学UppASD方法，系统计算研究合金化及温度对各相晶格体积、磁性质、弹性模量、自由能的影响；近似确定成分相界及相转变温度；探索合金化及温度影响磁热力学和相稳定性规律及关联和机理，为解释delta基钚合金优异性能，通过合理控制组分实现室温稳定和性能优化提供理论基础。

合理设计的面心立方钚基高温合金（δ基钚高温合金）可稳定于室温且具纯铝的良好加工性能，是目前核材料领域研究热点之一。随成分及制备工艺不同，δ基钚高温合金中除δ外，还会出现δ'和ε相，对其磁热力学性能有重要影响。了解各相性质并对其恰当控制，是实现δ基钚高温合金室温稳定和性能优化的关键。δ基钚合金剧毒放射性，极不便实验测量；此高温顺磁、具5f电子强相关及磁自旋波动的无序合金又为第一原理计算造成极大困难。目前人们对各相缺乏本质认识。.本项目采用第一性原理EMTO-CPA结合UppASD方法，借助于热力学公式和模型，充分考虑温度依赖的熵、晶格热振动、磁自旋波动等的影响，系统计算研究得出了合金化组分及温度对δ基Pu、Pu-Ga、Pu-Al、Pu-Zr、Pu-In高温合金中δ、δ'和ε各相的晶格体积、磁性质、弹性模量、自由能的影响规律；近似确定了它们成分相界和相转变温度、磁转变温度；揭示了合金化成分和温度影响它们相稳定性及磁热力学性能的规律性，并探讨了它们之间的相互关联和物理机理。.具体地，对于Pu，δ-ε相变的发生源于磁自旋波动、电子-声子耦合及晶格热效应共同作用的结果；δ-ε相变发生在Pu局域磁矩绝对值（μPu）在3.5 μB-4.0 μB之间，在800 K下，ε-Pu稳定存在于μPu=3.8 μB的磁状态。对于Pu-Ga（Pu-Zr），在AFM状态下，δ相稳定存在于Ga（Zr）浓度为15%-20%（10%-20%）区间；在PM状态下，δ相稳定存在于Ga（Zr）浓度小于15%。对于Pu-Al，随Al含量增加，δ相费米面电子峰变小，在四方变形下其劈裂的程度则变小，从而不利于δ-δ'-ε相变的发生。对于Pu-In，随In含量增加，Pu与In原子s、p电子间杂化、及Pu 5f电子局域占据均减弱，抑制了δ-ε相变，从而导致该相变温度随In含量增加而降低。.项目研究结果，为δ基Pu高温合金提供了有利的热力学数据库，为辨别不同合金组分的优异性能，及通过合理控制组分、实现δ基Pu高温合金室温稳定存在和性能的优化提供了理论基础，并能够指导实验验证, 从而有望后期应用于实际核工业、核能源和核燃料中。