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内部的运作。这项工作的目标是在地球深部的相关压力和温度条件下测量可能是主要的深部地幔矿物mgsio3的相稳定性、密度、压缩性和热弹性特性。在激光加热的金刚石细胞中进行原位高压测量以约束这些特性的能力受到金刚石细胞样品腔内样品行为的严重限制。样品几何-通常由嵌入在研究材料基体中的标记材料组成-将在测量中产生误差和不确定性。然而，当样品的几何形状得到控制时，测量的准确度和精度可以显著提高。这些改进是我们提出的工作的一个特点。具体任务包括：1)由MgSiO3和金属标记起始材料交替层组成的样品的溶胶-凝胶处理；2)研究样品室的应力环境，特别是激光加热过程中的应力环境；3)用于密度和压缩性测量的高压x射线衍射测量；4) x射线衍射耦合激光加热测定MgSiO3的相稳定性和约束热弹性；5)试样腔内应力状态的有限元模拟。研究结果在技术和科学前沿都具有重要意义。从技术上讲，这项研究将提高我们智能设计地球物理测量样本的能力。从科学上讲，这些结果将有助于我们了解最深的地幔如何帮助控制整个地球的现状和演化。

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.