Multiwavelength anomalous X-ray diffraction for combined imaging of atomic displacement and strain

The X-ray Bragg coherent diffractive imaging (CDI) technique assumes that the structure factor holds constant over the measured crystal. This approximation breaks down for materials exhibiting variations in the unit-cell configuration, such as piezo- and ferroelectrics. In that case, the strain field cannot be reliably determined from the reconstruction because the lattice deformation and the structure factor contribute concomitantly. Proposed here is a solution to this problem achieved by combining Bragg CDI and the multiwavelength anomalous diffraction approach that measures a Friedel pair of reflections at two different photon energies near an absorption edge. Comparing the obtained reconstructions with a parametric model that includes calculating the scattering amplitude as a function of wavelength and the unit-cell configuration, the contributions of the lattice deformation and the structure factor are separated. Simulations of the ferroelectric material BaTiO3 demonstrate the possibility of simultaneous probing of the strain and displacement of the Ti atoms. The proposed method opens up an opportunity to apply coherent X-ray diffraction for nanoscaleresolved 3D mapping of polarization domains in micro- and nanocrystals.

Automated summary

In materials with unit-cell configuration variations, a solution to reliably determine the strain field is proposed by combining Bragg CDI and multiwavelength anomalous diffraction. This approach separates the contributions of lattice deformation and structure factor, allowing for simultaneous probing of strain and displacement in materials like ferroelectrics. The method opens up an opportunity for nanoscale-resolved 3D mapping of polarization domains in micro- and nanocrystals using coherent X-ray diffraction.