  A general spherical harmonics method is described for extracting anisotropic
pair distribution functions (PDF) in this work. In the structural study of
functional crystallized materials, the investigation of the local structures
under the application of external stimuli, such as electric field and stress,
is in urgent need. A well-established technique for local structure studies is
PDF analysis, but the extraction of the X-ray PDF data is usually based on
angular integrations of isotropic X-ray structure functions, which is no longer
valid for the anisotropic responses of the materials under
orientation-dependent stimuli. Therefore, we have developed an advanced
spherical harmonics method to transform two-dimensional X-ray diffraction
patterns into anisotropic PDF data, based on three-dimensional diffraction
geometry and Fourier transform. The electrical-field-induced local structural
change in the PbZr0.54Ti0.46O3 ceramics is then presented to demonstrate the
method's effectiveness.
