High-Precision Equations of State Through Standardized Sample Synthesis

地球、太阳系中的行星和系外行星的组成、结构和演化，只能通过精确的模型来详细研究行星材料的压力、温度和密度之间的关系。该提案将设计微加工样品，以创建标准化样品，消除影响此类测量精度和准确性的许多复杂因素。这项工作的一个关键成果将是在多个实验室设施进行一系列“循环”实验，以评估样品质量、实验设施变化和分析方法的相对影响。由于拟议的实验方法将在每次合成中产生数千个相同的样品，这些样品将提供给更广泛的实验界，用于状态方程复制、相图和扩散研究以及电导率和热导率的测量。该提案将支持一名博士生和最多3名本科生的培训。所有数据和结论将在科学文献中发表，并在学术会议上发表。地核的成分是铁、镍和少量较轻元素的混合物，这一推论是由于认识到地核的密度低于纯铁或铁镍合金的密度。然而，推断轻元素的丰度和身份受到铁和铁镍合金热弹性性质的精确度和准确度的限制，因为轻元素的影响受到铁镍合金和核心物理性质之间差异的限制。为了评估地核条件下热弹性性质之间的差异，需要（1）端元物质的精确状态方程，以及（2）状态方程到地核条件的精确和准确的外推。该提案（1）将制定一项策略，通过比较不同实验方法在高精度测量时的影响来评估高压和高温下状态方程的准确性，以及（2）将量化外推状态方程的不确定性。这些目标将通过制造用于激光加热金刚石对顶砧单元的定制和可重复的样品来实现，重点是hcp和fcc铁和铁镍合金在高压和高温下的状态方程。在本提案的第二阶段，将在采用不同温度测量策略的多个同步加速器终端站设施重复测量。

The composition, structure, and evolution of the Earth, planets in the Solar System and exoplanets, can only be examined in detail with precise models for the relationship between pressure, temperature, and density of planetary materials. This proposal will engineer microfabricated samples to create standardized samples that eliminate many of the complications that affect the precision and accuracy of such measurements. A key outcome of the work will be a "round robin" series of experiments at multiple laboratory facilities to assess the relative effects of sample quality, variations in experimental facility, and analysis method. As the proposed experimental approach will produce thousands of identical samples in each synthesis, the samples will be available to the broader experimental community for equation of state replication, phase diagram and diffusion studies, and measurement of electrical and thermal conductivity. This proposal will support the training for a PhD student and up to 3 undergraduate students. All data and conclusions will be published in the scientific literature and presented at academic conferences. The inference that the composition of the Earth's core is a mixture of iron, nickel and a small amount of lighter elements arises from the recognition that the Earth's core has a density lower than that expected for pure iron or iron-nickel alloys. However, inferring the abundance and identity of light elements is limited by the precision and accuracy of the thermoelastic properties of iron and iron-nickel alloys, as the impact of light elements is constrained through the discrepancy between the physical properties of iron-nickel alloys and that of the core. To assess the differences between thermoelastic properties under Earth's core conditions requires (1) accurate equations of state of the end member substances, and (2) a precise and accurate extrapolation of equations of state to core conditions. This proposal (1) will develop a strategy to assess the accuracy of equations of state at high pressures and temperatures by comparing the impact of different experimental approaches when measured to high precision, and (2) will quantify the uncertainty of extrapolated equations of state. These goals will be accomplished through the manufacture of custom and reproducible samples for use in the laser-heated diamond anvil cell focusing on the equations of state of hcp and fcc iron and iron-nickel alloys to high pressure and temperature. In the second stage of this proposal, measurements will be repeated at multiple synchrotron end station facilities that employ differing temperature measurement strategies.