Temperature dependence of the thermal diffuse X-ray scattering from sodium single crystals

Abstract

We report on experimental results for the thermal diffuse X-ray-scattering cross section from Na single crystals. Data are presented for the [100], [110], and [111] directions taken in the temperature range from 38 K to the melting point. In addition we present a numerical calculation of the harmonic diffuse-scattering cross section including all orders of multiphonon contributions using a realistic phonon-dispersion relation. The results of this model are compared with a simpler approximation for the higher order multiphonon terms. The differences between the calculations and the experimental data show a distinct asymmetrical behaviour with respect to the reciprocal lattice points. Owing to this fact and their temperature dependence they can be related to anharmonic scattering. The contributions of the four lowest order terms are derived from the data. The lowest order antisymmetric contribution agrees quite well with available theoretical calculations.