Maximizing completeness in single-crystal high-pressure diffraction experiments: phase transitions in 2°AP

Sufficiently high completeness of diffraction data is necessary to correctly determine the space group, observe solid-state structural transformations or investigate charge density distribution under pressure. Regrettably, experiments performed at high pressure in a diamond anvil cell (DAC) yield inherently incomplete datasets. The present work systematizes the combined influence of radiation wavelength, DAC opening angle and sample orientation in a DAC on the completeness of diffraction data collected in a single-crystal high-pressure (HP) experiment with the help of dedicated software. In particular, the impact of the sample orientation on the achievable data completeness is quantified and proved to be substantial. Graphical guides for estimating the most beneficial sample orientation depending on the sample Laue class and assuming a few commonly used experimental setups are proposed. The usefulness of these guides has been tested in the case of luminescent 1,3-diacetylpyrene, suspected to undergo transitions from the alpha phase (Pnma) to the gamma phase (Pn2(1)a) and delta phase (P112(1)/a) under pressure. Effective sample orientation has ensured over 90% coverage even for the monoclinic system and enabled unrestrained structure refinements and access to complete systematic extinction patterns.

Automated summary

The research systematically analyzed the combined influence of radiation wavelength, DAC opening angle, and sample orientation on the completeness of diffraction data in high-pressure single-crystal experiments, providing graphical guides for estimating the optimal sample orientation. Effective sample orientation ensured over 90% coverage even for monoclinic systems, enabling unrestrained structure refinements and access to complete systematic extinction patterns.