Vibrational order in Pu0.98Ga0.02

In an earlier paper (Lawson et al., 2000, Phil. Mug. B, 80, 53) we described the measurement and interpretation of Debye-Waller factors in a δ-phase Pu 0.98 Ga 0.02 alloy. We concluded that the measurements could be described using a Debye model with a strongly temperature-dependent Debye-Waller temperature. In those experiments, we observed significant diffuse scattering in the neutron powder diffraction patterns. In this paper we describe a new technique for analysing diffuse scattering based on Rietveld analysis, and apply the technique to data for δ-phase Pu 0.98 Ga 0.02 and for Pb. The results from the correlations among lattice vibrations show that the diffuse scattering is Warren-Borie scattering and that the diffuse scattering is in basic agreement with that expected from the Debye model except that the scattering from the nearest-neighbour correlations in Pu 0.98 Ga 0.02 is anomalous at high temperatures. We also discuss the observation of significant anisotropic broadening of the diffraction peaks for Pu 0.98 Ga 0.02 at low temperatures.