XRD of gold and platinum to above 600 GPa.

The aim of this proposal is to extend XRD measurements of Au and Pt from 150 GPa to above 600 GPa under hydrostatic conditions using a Ne pressure-transmitting medium in a toroidal DAC. Simultaneous determination of the volumes of these three elements at various pressures will be useful to test and potentially refine the recently proposed calibration of gold and platinum, based on shockless compression experiments, as standards up to 1 TPa. Platinum is expected to remain in the fcc structure up to 1 TPa. While a sequence of fcc-hcp-bcc phase transitions has been predicted for gold, the transition pressures remain debated. Here, we expect to unambiguously observe the fcc-hcp transition by reaching slightly above 600 GPa. Finally, this data set will allow for a critical assessment of XRD measurements of these two elements under nanosecond compression, the current approach used to investigate the atomic structure of matter at TPa pressures.

本研究提案的目标为：借助环形金刚石对顶砧（toroidal Diamond Anvil Cell, DAC）内的氖（Neon, Ne）传压介质，在静水压条件下将金（Gold, Au）与铂（Platinum, Pt）的X射线衍射（X-ray Diffraction, XRD）测量范围从150吉帕斯卡（Gigapascal, GPa）拓展至600吉帕斯卡以上；同步测定这三种元素在不同压力下的体积，将有助于验证并优化近期基于无冲击压缩（shockless compression）实验提出的、可作为1太帕斯卡（Terapascal, TPa）以内标准的金与铂校准方案。铂预计在高达1太帕斯卡的压力下仍保持面心立方（face-centered cubic, fcc）结构，尽管学界已预测金会经历fcc-hcp-bcc的连续相变，但各相变的临界压力仍存在争议；本研究计划通过将压力提升至略高于600吉帕斯卡的水平，实现对金的fcc-hcp相变的明确观测。最终，本数据集将可用于批判性评估纳秒级压缩（nanosecond compression）条件下这两种元素的X射线衍射测量结果——该方法是当前用于探究太帕斯卡级压力下物质原子结构的主流实验手段。