What is DAFS and Why Is It Useful for BaTiO3?

In Diffraction Anomalous Fine Structure (DAFS) the energy dependence of the scattering intensity from a crystal is measured as the measurement energy is tuned across the resonant energy of one or more atoms in the crystal.

The resonant scattering factor for an atom is [5]

f(E,Q) = f_0(Q) + f'(E) + i f"(E) + Delta f"(E) * (chi'(E) + i chi"(E))

Delta f is the portion of f"(E) due solely to the resonant electron of the resonant atom and is modulated by the same complex chi(E) whose imaginary part is measured in XAFS.

The diffraction intensity

I(E,Q) ~= | sum over sites f(E,Q) * exp(i Q.R) |^2

is measured across the resonant energies of the material. The atomic anomalous scattering terms, f'(E) and f"(E) introduce rapid variation in the diffracted intensity in the energy region around the resonant energy. The Delta f"(E) * (chi'(E) + i chi"(E)) term introduces oscillatory structure to the DAFS above the resonant energy. These oscillations contain local structural information similar to that in XAFS.

 

[previous] [next] [table of contents]

Bruce Ravel

Last modified: Wed Feb 18 15:56:11 EST 1998