Discommensurations and diffraction patterns of thiourea

X-ray scattering from thiourea is investigated by the use of an ordinary X-ray source and synchrotron orbital radiation. Discommensurations in the modulated phases are recognized in diffraction patterns which contain high-order satellites. In the ferroelectric phase, diffusive peaks are observed. This indicates the existence of residual discommensurations as ferroelectric domain walls. The peculiar dielectric anomaly at 161 K of thiourea is discussed in connection with the residual discommensurations. (author)