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Published on: April 24, 2018
A noncrystallographic screw axis parallel to a twin axis can corrupt intensity statistics
1Institute of Mathematical Problems of Biology, Russian Academy of Sciences, Pushchino, Moscow Region 142290, Russian Federation. lunin@impb.psn.ru
Twinning detection methods may fail if a noncrystallographic screw axis is present. This can cause twinned crystals to appear statistically similar to untwinned ones, biasing intensity distribution analysis.
Area of Science:
- Crystallography
- Materials Science
- Diffraction Physics
Background:
- Twinning detection methods often rely on statistical differences in diffracted intensities between twinned and untwinned crystals.
- These methods assume distinct statistical properties for twinned and untwinned specimens.
Purpose of the Study:
- To investigate the impact of noncrystallographic screw axes on twinning detection.
- To analyze how such axes affect the statistical properties of diffracted intensities in twinned crystals.
Main Methods:
- Analysis of statistical properties of diffracted intensities.
- Comparison of intensity distributions for twinned and untwinned crystals under specific conditions.
- Examination of the influence of noncrystallographic screw axes parallel to the twinning axis.
Main Results:
- A significant portion of reflections in twinned specimens with a noncrystallographic screw axis can exhibit Wilson statistics.
- Up to 50% of reflections may erroneously appear typical of untwinned crystals.
- The overall distribution of observed intensities is biased towards the Wilson distribution.
Conclusions:
- Standard twinning detection methods may be unreliable in the presence of noncrystallographic screw axes.
- The presence of such axes can mask twinning by mimicking untwinned crystal statistics.
- Careful consideration of symmetry elements is crucial for accurate crystallographic analysis.
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