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

ABSTRACT: The influence of a diamond anvil cell (DAC) aperture, incident radiation wavelength and sample orientation in a DAC on the completeness of diffraction data collected at high pressure has been systematically analyzed. The considerable impact of sample orientation on achievable data completeness has been confirmed and quantified for all Laue classes in the form of graphical guides. These guides have been applied to predict sample orientation for structural analysis of a sample undergoing an orthorhombic → monoclinic phase transition under pressure which ensured over 90% completeness. 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 α phase (Pnma) to the γ phase (Pn21a) and δ phase (P1121/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.

SUBMITTER: Tchon D 

PROVIDER: S-EPMC8562673 | biostudies-literature |

REPOSITORIES: biostudies-literature