Chemical Ordering Phase Transitions in Intermetallic Nanoparticles

技术概述：本研究将探讨金属间金属合金纳米颗粒中化学有序相变的基本问题。具体来说，模拟和测量单个，低于10nm的纳米颗粒的化学顺序的定量程度，作为颗粒大小，颗粒组成，温度，过程和局部环境变化的函数，特别关注探索动力学和平衡稳定性的作用。研究将集中在L10合金，特别是来自FePt家族和CuAu的NixFe1-xPt。最终目标是了解纳米颗粒系统中的相变，并优化纳米颗粒的化学排序，以用于磁存储应用。对金属间纳米颗粒合金中化学有序的认识是有限的。平衡热力学模型与实验结果定性吻合，但定量拟合较差。这些缺陷导致了这样一个问题：我们对纳米粒子有序的理解是否受到有序动力学的限制，还是我们对平衡热力学的不完全理解？将测量相变的有序温度和有序参数作为粒度和加工条件的函数。将对原位TEM加热和非原位退火研究进行比较。单粒子测量和粒子间的变化将是这项工作不可或缺的一部分。所研究的材料是专门选择的，以提供一系列的热力学和动力学性质，便于比较。这些材料系统的计算建模将与实验紧密结合，以探索与实验的定量比较以及可能的动力学和热力学参数的相对作用。非技术总结：材料的相变被看作是结构或性能的重大变化。熔化，固体到液体的变化，就是一个例子。合金的化学有序/无序是相变在技术上的一个重要例子。未来的磁记录介质将由化学有序金属合金的纳米级颗粒制成。粒度已被证明对熔化相变化有很大的影响，同样，该计划将研究尺寸和组成变量对金属合金化学有序相变化的影响。对影响化学有序相变的因素的基本理解最终将有助于高密度磁数据存储的社会效益，并使纳米技术的应用进一步复杂化。支持和训练本科生和研究生使用专门的实验工具。该计划将进一步发展为此努力开发的单纳米颗粒分析技术。

TECHNICAL SUMMARY:The proposed research will explore the fundamental questions concerning the chemical ordering phase transition in nanoparticles of intermetallic metal alloys. Specifically, modeling and measurement of the quantitative extent of chemical order of individual, sub-10nm nanoparticles as a function of particle size, particle composition, temperature, and process and local environment variations with a specific focus to probe the role of kinetics and equilibrium stability. The study will focus on L10 alloys, specifically NixFe1-xPt from the FePt family and CuAu. The ultimate goal is to understand phase transitions in nanoparticle systems and to optimize nanoparticle chemical ordering for magnetic storage applications. The understanding of chemical ordering in intermetallic nanoparticle alloys is limited. Equilibrium thermodynamic models gives a qualitative match to experiment, but the quantitative fits are poor. These shortcomings lead to the question: Is our understanding of nanoparticle ordering limited by the ordering kinetics or our incomplete understanding of the equilibrium thermodynamics? The order-disorder temperature and the order parameter through the phase transition will be measured as a function of particle size and processing conditions. Both in-situ TEM heating and ex-situ annealing studies will be compared. Single particle measurements and particle-to-particle variations will be integral to this work. The materials for study are specifically chosen to give a range of thermodynamic and kinetic properties useful for comparison. Computational modeling on these material systems will be closely coupled with experiment to explore the quantitative comparison to experiment and the relative role of possible kinetic and thermodynamic parameters. NON-TECHNICAL SUMMARY:A phase change in a material is seen as a significant change in structure or properties. Melting, a solid to liquid change, is one example. Chemical ordering/disordering of alloys is one technologically important example of a phase change. Future magnetic recording media will be made with nanometer sized particles of chemically ordered metal alloys. Particle size has been shown to have a big effect on melting phase changes and similarly this program will study the effect of size and composition variables on chemical ordering phase changes in metal alloys. A fundamental understanding of the factors influencing the chemical ordering phase change would eventually contribute to the societal benefit of high density magnetic data storage and enable further sophistication in nanotechnology applications. Both undergraduate and graduate students will be supported and trained to use specialized experimental tools. The proposed program will further develop the single nanoparticle analysis techniques developed for this effort.