A thermal diffuse X-ray scattering investigation of the lattice dynamics of caesium iodide

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Abstract
Absolute measurements have been made of the total thermal diffuse scattering of CuK alpha X-rays from single oriented crystals of caesium iodide. Data have been obtained in the major symmetry directions and compared with the theoretical values of total thermal diffuse scattering calculated using the 'deformation dipole' (d.d.) lattice dynamical data of Karo and Hardy (1968). In particular the results are used to discriminate between two variations of the d.d. model, demonstrating the unsuitability of the d.d. (+) variation and the good overall agreement with the d.d. (-) variation. Where feasible, the experimental thermal diffuse scattering has been analysed to yield acoustic and optic phonon dispersion curves. Finally, the discrepancies between the total experimental thermal diffuse scattering and the d.d. (-) theory predictions have been investigated for any asymmetry.