Herlihy Anna, Geddes Harry S, Sosso Gabriele C, Bull Craig L, Ridley Christopher J, Goodwin Andrew L, Senn Mark S, Funnell Nicholas P
Department of Chemistry, University of Warwick, Gibbet Hill, Coventry CV4 7AL, United Kingdom.
ISIS Neutron and Muon Facility, Rutherford Appleton Laboratory, Didcot OX11 0QX, United Kingdom.
J Appl Crystallogr. 2021 Nov 23;54(Pt 6):1546-1554. doi: 10.1107/S1600576721009420. eCollection 2021 Dec 1.
High pressure is a powerful thermodynamic tool for exploring the structure and the phase behaviour of the crystalline state, and is now widely used in conventional crystallographic measurements. High-pressure local structure measurements using neutron diffraction have, thus far, been limited by the presence of a strongly scattering, perdeuterated, pressure-transmitting medium (PTM), the signal from which contaminates the resulting pair distribution functions (PDFs). Here, a method is reported for subtracting the pairwise correlations of the commonly used 4:1 methanol:ethanol PTM from neutron PDFs obtained under hydro-static compression. The method applies a molecular-dynamics-informed empirical correction and a non-negative matrix factorization algorithm to recover the PDF of the pure sample. Proof of principle is demonstrated, producing corrected high-pressure PDFs of simple crystalline materials, Ni and MgO, and benchmarking these against simulated data from the average structure. Finally, the first local structure determination of α-quartz under hydro-static pressure is presented, extracting compression behaviour of the real-space structure.
高压是探索晶体结构和相行为的强大热力学工具，目前已广泛应用于传统晶体学测量中。迄今为止，使用中子衍射进行的高压局部结构测量受到强散射、全氘化压力传递介质（PTM）的限制，该介质的信号会污染所得的对分布函数（PDF）。本文报道了一种从静水压缩下获得的中子PDF中减去常用的4:1甲醇:乙醇PTM的成对相关性的方法。该方法应用分子动力学启发的经验校正和非负矩阵分解算法来恢复纯样品的PDF。原理验证得到了证明，生成了简单晶体材料镍和氧化镁的校正高压PDF，并将其与平均结构的模拟数据进行了对比。最后，给出了静水压力下α-石英的首次局部结构测定结果，提取了实空间结构的压缩行为。
