Diffraction satellites in indium caused by thermal-diffuse scattering

An x-ray search for charge-density-wave structure in indium revealed more than one hundred diffraction peaks having half integral (h,k,l). However, the "satellite" intensities were found to he proportional to temperature (above 20 K), which proves they are caused by thermal-diffuse scattering (TDS) involving phonons near the {1/2, 1/2, 1/2} points of the Brillouin-zone boundary. Theoretical TDS peaks, which were caculated for forty half-integral {h,k,l} families, explain the observed intensities. The peaks arise from a sharp dip in the slow shear phonon mode near {1/2,1/2,1/2} for q-space trajectories nearly parallel to the hexagonal face of the relevant extended zone boundary. (TDS peaks do not appear in scans along trajectories that are nearly perpendicular to the hexagonal face of an extended zone boundary.) The dynamic pseudopotential model for lattice vibrations in metals was employed. [S0163-1829(99)03919-3].