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Chirality-induced 'forbidden' reflections in X-ray resonant scattering
V E Dmitrienko1, E N Ovchinnikova
1A. V. Shubnikov Institute of Crystallography, 117333 Moscow, Russia.
Acta Crystallographica. Section A, Foundations of Crystallography
|October 27, 2001
Summary
Local chirality in non-magnetic crystals can create new Bragg reflections. This phenomenon, linked to asymmetric atomic environments, enhances scattering via mixed multipole transitions, even in centrosymmetric crystals.
Area of Science:
- Solid-state physics
- Crystallography
- Materials science
Background:
- Bragg reflections are typically explained by the symmetric arrangement of atoms in crystal lattices.
- The influence of local atomic chirality on diffraction patterns in non-magnetic crystals is not fully understood.
- Spatial dispersion effects, particularly those involving antisymmetric tensor components, are crucial for understanding complex scattering phenomena.
Purpose of the Study:
- To demonstrate the emergence of additional Bragg reflections due to local chirality in non-magnetic crystals.
- To investigate the dependence of these reflections' structure amplitude on the antisymmetric part of a third-rank tensor.
- To explore the role of resonant near-edge scattering and mixed multipole transitions in enhancing these reflections.
Main Methods:
- Theoretical analysis of scattering mechanisms in crystals with local chirality.
- Investigation of structure amplitude dependence on spatial dispersion effects described by third-rank tensors.
- Consideration of resonant near-edge scattering involving dipole-quadrupole transitions.
- Application of the theory to specific examples like alpha-Fe2O3 and LiNbO3.
Main Results:
- Additional Bragg reflections can arise solely from the local chirality of scattering atoms in non-magnetic crystals.
- The structure amplitude of these reflections is directly related to the antisymmetric part of the spatial dispersion tensor.
- Resonant near-edge scattering, particularly with dipole-quadrupole contributions, significantly enhances these chiral reflections.
- The mechanism is effective even in centrosymmetric crystals, as exemplified by alpha-Fe2O3 and LiNbO3.
Conclusions:
- Local atomic chirality is a fundamental mechanism for generating distinct Bragg reflections in non-magnetic materials.
- The observed reflections are governed by higher-order multipole transitions and antisymmetric tensor components.
- The interference between dipole-quadrupole and quadrupole-quadrupole terms may explain specific azimuthal dependencies in hematite (alpha-Fe2O3) reflections.