Harnessing Sample Geometry to Measure Equation of State of Deep Earth Minerals

矿物在超高压和高温下的行为控制着地球的内部运作。这项拟议工作的目标是测量在地球深处相关的压力和温度条件下，可能是主要深部地幔矿物--硅酸镁--的相稳定性、密度、可压缩性和热弹性性质。在激光加热的钻石池中进行现场高压测量以限制这些特性的能力受到钻石池样品腔内样品的行为的严重限制。样本几何图形--通常由嵌入研究材料矩阵中的标记材料组成--将在测量中产生误差和不确定性。然而，当控制样品几何形状时，可以显著提高测量的准确度和精密度。这些改进是我们拟议工作的一个特点。具体任务包括：1)由交替层的镁硅和金属标记物组成的样品的溶胶-凝胶处理；2)样品室的应力环境研究，特别是在激光加热期间。3)高压X射线衍射测量密度和压缩性；4)X射线衍射与激光加热相结合，以确定镁SiO_3的相稳定性和限制其热弹性性能；以及5)样品室内应力状态的有限元模拟。这一结果在技术和科学方面都具有重要意义。从技术上讲，这项研究将提高我们智能设计用于地球物理测量的样本的能力。从科学上讲，这些结果将有助于我们理解最深的地幔如何帮助控制整个地球的当前状态和演化。

The behavior of minerals at ultrahigh pressures and temperatures controls the inner workings of the Earth. The goals of this proposed work are to measure phase stability, density, compressibility, and thermoelastic properties of what is likely the predominant deep-mantle suite of minerals-MgSiO3-at the relevant pressure and temperature conditions of the deep Earth. The ability of in-situ high pressure measurements in the laser heated diamond cell to constrain these properties has been severly limited by the behavior of the sample inside the diamond cell sample chamber. The sample geometry-which often consists of a marker material embedded in the study material matrix-will generate errors and uncertainties in measurement. However, the accuracy and precision of measurements can be significantly improved when the sample geometry is controlled. These improvements are a feature of our proposed work. The specific tasks include: 1) Sol-gel processing of samples consisting of alternating layers of MgSiO3 and metal marker starting materials; 2) Studies of the stress environment of the sample chamber, especially during laser heating.; 3) X-ray diffraction measurements at high pressures for density and compressibility measurements; 4) X-ray diffraction coupled with laser heating to determine phase stability and constrain thermoelastic properties of MgSiO3; and 5) Finite element modeling of the stress state inside the sample chamber. The results have important implications on both technical and scientific fronts. Technically, this research will advance our ability to intelligently design samples for geophysical measurements. Scientifically, the results will contribute to our understanding of how the deepest mantle helps govern the current state and evolution of the whole Earth.