IUCr journals

Resonant scattering and multiple Bragg X-ray diffraction in LaMnO3; a classical view

Acta Cryst. (2006). A62, 459–462 [doi:10.1107/S010876730603889X]

[resonant scattering]Intensity vs. azimuthal angle for the 10-4 in proximity of full excitation of the -1-20. The 10-4 Bragg reflection is centered at 148.4°. The asymmetry of the profile is clearly visible and is a phase effect, corresponding to a particular model for the charge density.
The mechanism for resonant scattering in LaMnO3 has been the subject of some controversy between two competing models, leading to different d-electron densities. Forbidden reflections like 300 and 10-4 are turned on by resonance. Three-beam diffraction can be used to resolve ambiguities in determining valence electron densities obtained by means of resonant scattering. The choice between a negative and a positive structure factor is a particular aspect of the phase problem for which the technique of three-beam diffraction is particularly suited.

R. Colella and Q. Shen