The correction of measured integrated Bragg intensities for first order thermal diffuse scattering

The correction for the contribution of first-order thermal diffuse scattering to the measured integrated Bragg intensities of cubic single crystals has been derived by Nilsson (Ark. Fys. (1957) 12, 247). Nilsson's formulation applies to diffractometer measurements using an ω scan (crystal rotating, detector stationary) and involves the approximation of an infinite slit height. In this paper the corresponding result for a θ–2θ scan (detector coupled 2:1 to the crystal) is given and a further analytical method which approximates the volume scanned in reciprocal space to a sphere is discussed. The analysis for both ω and θ–2θ scans is extended in order to eliminate some of the approximations involved in the other methods; the limitations of the various methods are discussed and the results of example calculations are presented.