Structure factor amplitudes from thermal diffuse scattering measurements

A method is proposed, for certain single crystals, of estimating the structure factor amplitudes corresponding to Bragg reflexions with strong to medium integrated intensities from measurements of the thermal diffuse X-ray scattering in regions of reciprocal space close to the appropriate lattice points. The values obtained conventionally from integrated Bragg intensities are often subject to considerable error due to extinction effects. The thermal diffuse scattering, being incoherently scattered and of a relatively weak intensity, would appear to be less likely to be affected by primary and secondary extinction. The structure factor amplitudes (or correction factors for those found from Bragg measurements) are obtained from the observed scattering data by a least-squares refinement method. Procedures are suggested for use where measurements are made on (i) a relative scale, (ii) an absolute scale, with respect to the direct beam intensity. The method is illustrated by application to some single-crystal data.