Neutron-diffraction study of thiourea under high electric field

The modulation wave vector $\delta {\overrightarrow{\mathrm{b}}}^{*}$ of deuterated thiourea is measured as a function of temperature and for several electric-field values, using neutron diffraction. The only commensurate phase stabilized by the field is found to correspond to $\delta =\frac{1}{8}$. High-order commensurate phases such as $\delta =\frac{2}{15}, \frac{4}{29}, \mathrm{and} \frac{6}{43}$ are not observed, in contrast with a recent high-field x-ray diffraction study. The disagreement between the two techniques is ascribed to radiation damage caused by the x-ray beam itself. Perliminary results on an x-ray irradiated sample are presented.