The calculation and interpretation of multiphonon X-ray scattering - example of cubic zincblende structure compounds

The problems of making calculations using the total phonon scattering cross section in the harmonic approximation are examined and it is found that the method of Reid & Smith [J. Phys. C (1970), 3 1513- 1526] can be extended to cope with any material with a modest number of atoms per unit cell. Complex eigenvectors and complex scattering factors may be handled without approximations. The method is used to evaluate the multiphonon scattering (and one-phonon scattering) for a number of cubic zincblende structure compounds including GaAs, CdTe, CuI and SiC, taking eigendata from good lattice dynamical models. The results illustrate a discussion of the typical behaviour of multiphonon scattering as a function of scattering vector and temperature. The effect of anomalous dispersion on the total phonon scattering cross section is also shown and a discussion given of the origin of multiphonon processes, with particular reference to the contribution of these processes to the diffuse scattering observed near Bragg reflections. It is also concluded that dynamic deformation will not significantly affect multiphonon intensities.