Recovering local structure information from high-pressure total scattering experiments

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 hydrostatic 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 alpha-quartz under hydrostatic pressure is presented, extracting compression behaviour of the real-space structure.

Automated summary

High pressure is a powerful thermodynamic tool in exploring crystalline structure and phase behavior, but local structure measurements using neutron diffraction have been limited by the presence of a pressure-transmitting medium (PTM). This study introduces a method to subtract the influence of PTM and successfully obtain high-pressure PDFs for crystalline materials. Corrected high-pressure PDFs of simple crystalline materials and the first local structure determination of alpha-quartz under hydrostatic pressure are demonstrated.