Towards Pressure Triggered Phase Transition, an Experimental Observation of Charge Density Redistribution in Gypsum

Gypsum CaSO4·2H2O is one of the most common hydrated minerals in Earth’s crust. In this project we focus on the high pressure (>4 GPa) phase transition to gypsum-II to experimentally determine quantitative charge density redistribution. The use of quantum crystallography offers a better understanding of interactions within the crystal and its energetic properties. Multipole density model refinement demands excellent quality of single-crystal XRD data, characterized by high resolution and completeness. Moreover, Diamond Anvil Cell (DAC) restricts access to reciprocal space and introduces experimental noise.
ID-27 at ESRF offers exceptional solutions, very well collimated X-ray beam, extra stabilisation of the whole data collection system, excellent detector, high brilliance of the beam. These factors effectively address all the experimental challenges. Proposed research will enhance the role of quantum-crystallography in Earth and material sciences at high pressure.

石膏（CaSO₄·2H₂O）是地壳中最为常见的含水矿物之一。本项目聚焦于压力大于4 GPa时石膏向石膏-II相的相变过程，旨在通过实验定量测定电荷密度的重新分布情况。量子晶体学（quantum crystallography）的应用可帮助我们更深入地理解晶体内部的相互作用及其能量特性。多极密度模型精修对单晶X射线衍射（X-ray Diffraction, XRD）数据的质量要求极高，此类数据需具备高分辨率与高完备性。此外，金刚石对顶砧（Diamond Anvil Cell, DAC）会限制倒易空间的探测范围，并引入实验噪声。欧洲同步辐射装置（European Synchrotron Radiation Facility, ESRF）的ID-27线站具备优异的实验条件：高度准直的X射线束、整套数据采集系统的额外稳定化配置、高性能探测器以及高亮度的入射光束。这些因素可有效解决上述所有实验挑战。本项研究将进一步强化量子晶体学在高压地球科学与材料科学中的应用价值。